DNV-RU-SHIP Pt.4 Ch.5 Rotating machinery - driven units

RULES FOR CLASSIFICATION

Ships

Edition July 2021

Part 4 Systems and components

Chapter 5 Rotating machinery - driven units

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FOREWORD

DNV rules for classification contain procedural and technical requirements related to obtaining andretaining a class certificate. The rules represent all requirements adopted by the Society as basisfor classification.

© DNV AS July 2021

Any comments may be sent by e-mail to [email protected]

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of thisdocument. The use of this document by other parties than DNV is at the user's sole risk. Unless otherwise stated in an applicable contract,or following from mandatory law, the liability of DNV AS, its parent companies and subsidiaries as well as their officers, directors andemployees (“DNV”) for proved loss or damage arising from or in connection with any act or omission of DNV, whether in contract or in tort(including negligence), shall be limited to direct losses and under any circumstance be limited to 300,000 USD.

CHANGES – CURRENT

This document supersedes the July 2019 edition of DNVGL-RU-SHIP Pt.4 Ch.5.The numbering and/or title of items containing changes is highlighted in red.

Changes July 2021, entering into force 1 January 2022

Topic Reference Description

Fatigue property of propellerblade material

Sec.1 [2.2.1] Fatigue test procedure has been updated and described moreclearly now. The guidance note has been moved to DNVGL-CG-0039.

Introducing new requiredsafety factor for bladedimensioning based on CFDand FE

Sec.1 [2.2.2] andSec.1 Table 6

New safety factors for blade dimensioning following introductionof direct assessment of blade strength using CFD combined.

FE report for special propellerdesigns

Sec.1 [2.2.5] Revised paragraph. Documentation of FE report is described inDNVGL-CG-0039 for all propellers.

Strengthening of propellerblade of azimuth thrusters incrash stop operation

Sec.1 [2.2.7] The text has been amended to clarify requirements for propellerblades for azimuth thrusters versus loads in crash stops.

Sec.1 [2.3.2] An alternative method using FE has been introduced for thestatic strength evaluation of CP components.

Sec.1 Table 8 Table 8 has been updated presenting new required safety factorwhen using FE analysis.

Sec.1 [2.3.6] Clear and unambiguous requirements for the considerationof realistic load cycles and loads dynamics for the strengthevaluation.

Strength evaluation of CPsystem components based onFE

Sec.1 [2.3.7] Guidance note has been removed.

Thickness of hub cap fin Sec.1 [2.3.12] Guidance note text on required thickness for the hub cap finhas been modified.

Pretention of blade bolt Sec.1 [2.4.1] The text has been clarified.

Rebranding to DNV All This document has been revised due to the rebranding of DNVGL to DNV. The following have been updated: the companyname, material and certificate designations, and references toother documents in the DNV portfolio. Some of the documentsreferred to may not yet have been rebranded. If so, please seethe relevant DNV GL document.

Editorial correctionsIn addition to the above stated changes, editorial corrections may have been made.

Part 4 Chapter 5 Changes - current

Rules for classification: Ships — DNV-RU-SHIP Pt.4 Ch.5. Edition July 2021 Rotating machinery - driven units

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CONTENTS

Changes – current.................................................................................................. 3

Section 1 Propellers................................................................................................ 81 General................................................................................................ 81.1 Application....................................................................................... 81.2 Documentation................................................................................. 81.3 Required compliance documentation..................................................10

2 Design................................................................................................122.1 General..........................................................................................122.2 Criteria for propeller blade dimensions.............................................. 132.3 Pitch control mechanism and propeller hub........................................ 142.4 Fitting of propeller blades to the hub................................................ 16

3 Inspection and testing.......................................................................173.1 General..........................................................................................173.2 Inspection and testing of parts.........................................................18

4 Workshop testing...............................................................................184.1 General..........................................................................................18

5 Control and monitoring......................................................................185.1 General..........................................................................................18

6 Arrangement......................................................................................206.1 General..........................................................................................206.2 Arrangement of propeller.................................................................206.3 Hydraulic system for pitch control.....................................................20

7 Vibration............................................................................................ 207.1 General..........................................................................................20

8 Installation inspection....................................................................... 208.1 General..........................................................................................208.2 Fitting of propeller and propeller blades.............................................208.3 Pitch marking................................................................................. 208.4 Hydraulic piping..............................................................................21

9 Shipboard testing.............................................................................. 219.1 Sea trial........................................................................................ 21

Section 2 Water jets............................................................................................. 221 General.............................................................................................. 221.1 Application..................................................................................... 221.2 Documentation............................................................................... 22

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1.3 Required compliance documentation..................................................231.4 Definitions......................................................................................25

2 Design................................................................................................262.1 General..........................................................................................262.2 Design of components..................................................................... 26

3 Inspection and testing.......................................................................273.1 General..........................................................................................273.2 Testing and inspection of parts.........................................................273.3 Assembling.....................................................................................27


5 Control, alarm, safety functions and indications................................285.1 General..........................................................................................285.2 Monitoring and bridge control...........................................................28

6 Arrangement......................................................................................296.1 General..........................................................................................29

7 Vibration............................................................................................ 307.1 General..........................................................................................30

8 Installation survey.............................................................................308.1 Surveys......................................................................................... 30

9 Shipboard testing.............................................................................. 309.1 General..........................................................................................30

Section 3 Podded and geared thrusters................................................................ 321 General.............................................................................................. 321.1 Introduction................................................................................... 321.2 Objective....................................................................................... 321.3 Scope............................................................................................ 321.4 Application..................................................................................... 321.5 Definitions and symbols...................................................................331.6 Documentation............................................................................... 361.7 Required compliance documentation..................................................411.8 Workmanship..................................................................................43

2 Arrangement and operation...............................................................432.1 General..........................................................................................432.2 Thrusters serving main function propulsion........................................ 432.3 Thrusters serving main function steering........................................... 432.4 Operation of propulsion thrusters serving main functions..................... 45

3 Design................................................................................................46



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3.1 General..........................................................................................463.2 Housing......................................................................................... 473.3 Propulsion line................................................................................483.4 Azimuth steering gear for thrusters...................................................493.5 Auxiliary systems............................................................................533.6 Vibration........................................................................................ 543.7 Special design features....................................................................563.8 Control and monitoring systems....................................................... 56

4 Inspection and testing.......................................................................624.1 General..........................................................................................624.2 Workshop testing............................................................................ 634.3 Installation on board....................................................................... 654.4 Sea trial........................................................................................ 66

5 Required compliance documentation in other rules chapters............. 67

Section 4 Compressors..........................................................................................701 General.............................................................................................. 701.1 Application..................................................................................... 701.2 Definitions......................................................................................701.3 Documentation............................................................................... 711.4 Required compliance documentation..................................................73

2 Design................................................................................................762.1 Materials........................................................................................762.2 Reciprocating compressors............................................................... 762.3 Non-reciprocating compressors......................................................... 782.4 Containment...................................................................................792.5 Piping and arrangement.................................................................. 79

3 Inspection and testing.......................................................................803.1 General..........................................................................................803.2 Inspection of the parts.................................................................... 80


5 Control and monitoring......................................................................815.1 General..........................................................................................81

6 Arrangement on-board...................................................................... 826.1 General..........................................................................................82

7 Vibration............................................................................................ 827.1 Torsional vibration...........................................................................82

8 Installation inspection....................................................................... 83



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8.1 Installation onboard........................................................................ 838.2 Vibration........................................................................................ 83

Changes – historic................................................................................................84



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SECTION 1 PROPELLERS

1 General

1.1 Application

1.1.1 The rules in this section apply to propellers intended for propulsion, steering and manoeuvring.Ch.2 describes all general requirements for rotating machinery and forms the basis for all sections in Ch.3,Ch.4 and Ch.5.

1.1.2 The following items are recognised as parts of the propeller and are subject to approval:

— propeller blades— blade fitting mechanism (e.g. blade bolts - if any)— propeller hub— pitch control mechanism (if any).

For fitting of the propeller to the shaft, see Ch.4 Sec.1.

1.1.3 See Pt.6 Ch.6 Sec.2 concerning propellers for ships with ice strengthening.

1.1.4 See Pt.5 Ch.13 concerning additional requirements for propellers for naval vessels.

1.1.5 See Pt.6 Ch.2 Sec.7 concerning additional requirements related to redundant propulsion.

1.1.6 See Pt.6 Ch.3 Sec.1 and Pt.6 Ch.3 Sec.2 concerning additional requirements related to dynamicpositioning systems.

1.2 Documentation

1.2.1 The builder shall submit the documentation required by Table 1.

Table 1 Documentation requirements

Object Documentation type Additional description Info

C020 - Assembly or arrangementdrawing FI

C030 – Detailed drawing

Detailed geometry, including:

— verification details of fitting of hub topropeller shaft

— hub cap with fins and cap bolts (asapplicable)

— blade fitting arrangement (asapplicable).

Material specification, properties and heattreatment.

AP

C040 – Design analysis Fitting calculation. FI, R

Hub

Z162 - Installation manual Shall follow each delivery. FI, R

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C030 - Detailed drawingDetailed geometry, including blade flange,as applicable. Material specification,properties and heat treatment.

AP

Blade

C040 – Design analysis

FE calculation (mandatory for specialdesigns), including backgrounddocumentation:

— detailed hydrodynamic calculation— wake field data.

(Blade geometry data file in ASCII format,preferably PFF may be requested).

FI, R

Controllable pitch servomechanism C030 - Detailed drawing

Detailed geometry of all load carryingparts, such as servo cylinder, piston andpiston rod.


AP

S042 - Hydraulic control diagramIncluding permissible operating servopressures, specification of oil filter, andalarm list with setpoint and relay times.

AP

Z161 - Operation manual If pitch adjustment is used as load controlof propeller driver. FI, R


C030 - Detailed drawing

Detailed geometry of all load carryingparts, such as crank disc, push pull rod,cross head and sliding shoe.


AP

Controllable pitchmechanism

C040 – Design analysisAnalysis including description of pitchpropeller system is mandatory for newdesign.

FI, R

Control and monitoringsystem

I200 - Control and monitoring systemdocumentation According to Ch.9. AP

AP = For approval; FI = For information; R = On request

1.2.2 For general requirements for documentation, including definition of the info codes, see DNV-CG-0550Sec.6.

1.2.3 For a full definition of the documentation types, see DNV-CG-0550 Sec.5.

1.2.4 Relevant design parameters shall be given. As a minimum, the following shall be specified:

— engine power at maximum continuous rating (MCR)— corresponding propeller rotational speed— maximum ship speed— design pressure of hydraulic pitch system (if any)— relevant additional class notations (see [1.1.3] - [1.1.6]).



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The manufacturing tolerance class (ISO 484) shall be specified on the propeller drawings.

1.2.5 The following additional information shall also be submitted for the propeller:

— weight and buoyancy— polar and diametrical mass moment of inertia in air— polar and diametrical mass moment of inertia of entrained water (for zero and full pitch for CP propellers)— predicted operational hydraulic pressure for controllable pitch propellers, when available.

1.2.6 For instrumentation and automation, including computer based control and monitoring, see Ch.9.

1.3 Required compliance documentation

1.3.1 Pumps, electric motors, coolers, piping, filters, valves, etc. that are delivered as integral parts of thehydraulic operation and cooling systems, shall be checked as found relevant by the propeller manufacturer’squality system.

1.3.2 Compliance documents shall be issued as per Table 2 and scope of testing and inspection ofcomponents as per Table 3.

Table 2 Compliance documents

ObjectCompliancedocumenttype

Issued by Compliancestandard* Additional description

PC

MC

NDT (See Pt.2 Ch.2 Sec.7 and Pt.2 Ch.2Sec.10).

Propellers cast in one piece

PTR

Society

Dimension control (see [3.1.9]).

PC

MC

NDT (See Pt.2 Ch.2 Sec.7 and Pt.2 Ch.2Sec.10).

Separate blades

PTR

Society

Dimension control (see [3.1.9]).

MC Society PC and MC may be issued bymanufacturer for axillary propeller.

NDT Society (See Pt.2 Ch.2 Sec.7 and Pt.2 Ch.2Sec.10).Separate hubs

NDT Manufacturer (See Pt.2 Ch.2 Sec.7 and Pt.2 Ch.2Sec.10).

MTRHub cap with fins

PTRManufacturer

Dimension control

Blade bolts PC Society PD may be issued by manufacturerfor auxiliary propeller.



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MD Manufacturer

NDT Manufacturer

MD

Crank disc, push pull rod, servocylinder and cross head.

Other parts of pitching mechanismupon request.

Controllable pitch mechanism

NDT

ManufacturerNDT shall cover highly stressedareas, such as blade bolts, crankdisk fillet, threads of push-pullrods, etc.

Pitch control and monitoringsystem PC Society See Ch.9.

PC = product certificate

MC = material certificate

MD = material declaration

MTR = material test report

PTR = product test report

NDT = NDT report

*Unless otherwise specified the compliance standard is the Society rules.

1.3.3 For general certification requirements, see DNV-CG-0550 Sec.4.

1.3.4 For a definition of the certification types, see DNV-CG-0550 Sec.3.

1.3.5 The surveyor shall do visual inspection of parts. Visual inspection shall include random dimensionalcheck with emphasis on critical dimensions, tolerances and stress raisers.Manufacturer’s measurement report shall be presented for main items and shall be available upon request forminor components.Manufacturer’s survey report shall be available upon request.

Table 3 Testing and inspection of components

ComponentMaterial test (chemicalcomposition and

mechanical properties)

Magneticparticle

inspection ordye penetrant

Visual anddimensional inspection

Propellers cast in one piece Society Society Society1)

Separate blades Society Society Society1)

Separate hubs Society or manufacturer2) Manufacturer3) Society or manufacturer2)

Hub cap with fins Manufacturer

Blade bolts Society or manufacturer2) Manufacturer Manufacturer



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ComponentMaterial test (chemicalcomposition and

mechanical properties)

Magneticparticle

inspection ordye penetrant

Visual anddimensional inspection

Crank disc, push pull rod, servo cylinderand cross head. Other parts of pitchingmechanism when found necessary

Manufacturer Manufacturer4) Manufacturer

The propeller shall be delivered with a Society’s certificate, see [1.1.1]. Reference is also given to [1.1.2].

1) See also [3.1.9]2) The Society if propulsion.3) Only required in A and C zones (see Pt.2 Ch.2 Sec.8 and Pt.2 Ch.2 Sec.11 [3]).4) Only required in highly stressed areas, such as blade bolts, crank disk fillet, threads of push-pull rods, etc.

2 Design

2.1 General

2.1.1 Materials for propellers shall comply with the requirements in Pt.2 Ch.1 and Pt.2 Ch.2.For other materials, particulars of mechanical properties and chemical compositions shall be submitted tothe Society. Fatigue properties different from the ones given in Table 4 may be accepted, provided sufficientdocumentation is presented.

Table 4 Material properties

MaterialMaterial constantU1 [N/mm

2]Material constant

U2 [-]Minimum yield strength

σy [N/mm2]

Minimum tensile strengthσB [N/mm

2]

Mn-Bronze, CU1(High tensile brass)

55 0.15 175 440

Mn-Ni-Bronze, CU2(High tensile brass)

55 0.15 175 440

Ni-Al-Bronze, CU3 80 0.18 245 590

Mn-Al-Bronze, CU4 75 0.18 275 630

Martensitic stainless steel(12Cr 1Ni)

60 0.20 440 590


65 0.20 550 750


70 0.20 540 760

Austenitic stainless steel(19Cr 11Ni)

55 0.23 180 440

Forged steel and other materials shall be especially considered.



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Guidance note:Class guideline DNV-CG-0039 offers guidance on how fatigue properties may be documented by fatigue testing.Alternative methods may also be considered on the basis of equivalence, see Pt.1 Ch.1 Sec.1 [2.5.9].

---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---

2.1.2 The requirements given in [2.2], [2.3], and [2.4] apply to all propellers of conventional design andarrangement, unless otherwise explicitly stated. For propellers not recognised as conventional by the Society(e.g. surface piercing propellers, tip fin propellers, cycloidal propellers etc.), the approval shall be based onspecial consideration.

2.1.3 The combination of materials shall be such as to minimise galvanic corrosion.

2.1.4 The surface of the hub, conical bores, fillets and blades shall be smoothly finished.

2.2 Criteria for propeller blade dimensions

2.2.1 The following load conditions shall be considered:

a) High cycle dynamic stresses (> 108 cycles) due to rotational propeller load variation in normal, aheadoperation.

b) Low cycle dynamic stresses (< 106 cycles) due to propeller load variations in a seaway, manoeuvres,starting and stopping, reversing, repetitive ice shock loads etc. shall also be considered when dynamicstresses are not dominated by high cycle load variations, e.g. for propellers for which turning directionmay be reversed and propellers running in undisturbed axial inflow.Guidance note:Class guideline DNV-CG-0039 offers detailed methods on how to assess the minimum safety factors in Table 5, alternatively Table6 for these load conditions.Other methods may also be considered on the basis of equivalence.


2.2.2 The propeller blades shall be designed with the minimum safety factors as given in Table 5 providedthat the analytic methodology and formula described in DNV-CG-0039 are used for the strength assessment,see also guidance note in [2.2.1]. The safety factors reflect the expected inaccuracies in the methods usedfor predictions of loads and stress calculations, as well as the influence of allowable material defects.The tabulated safety factors also apply provided that manufacturing tolerance class I or S is specifiedaccording to ISO484 for propulsion propellers. (Tolerance class II or better for other propellers.)Otherwise higher safety factors may be required, based upon special consideration.

Table 5 Minimum safety factors for propeller blades, analytic calculation

Load conditionApplication Considered section

Static Low cycle fatigue High cycle fatigue

At root section - - 1.8All propellers, exclusive tunnel thrusters

At 0.6R - - 1.6

Reversible direction of rotation,exclusive tunnel thrusters At 0.8R - 1.5 -

Tunnel thrusters At root section 2.2 - -

2.2.3 Lower safety factors than given in Table 5 may be accepted after special consideration if dynamicstresses are documented by means of reliable measurements and/or advanced calculation method, such as



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CFD calculation combined with FE analysis, see DNV-CG-0039. When detailed calculations are carried outaccording to DNV-CG-0039, safety factors according to Table 6 will be accepted.

Table 6 Minimum safety factors for propeller blades, CFD calculations and FE analysis

Load conditionApplication Considered section

Low cycle fatigue High cycle fatigue

At root - 1.5All propellers

All sections above root - 1.4

Reversible direction ofrotation All sections 1.3

2.2.4 Blade root fillet shall be designed in order to maintain a safety factor in the fillet as required for theroot section. Fillets with constant radius of 75% of root thickness, or multi-radius fillets of a “constant stress”design are considered to comply with this requirement.

2.2.5 For calculation of the blade stress of special propeller designs such as tip fin propellers, special profiles,etc., FE calculation shall be submitted with documented details of the hydrodynamic loads, see also DNV-CG-0039.

2.2.6 If the propeller is subjected to an essential wear e.g. by abrasion in tidal flats or dredgers, a wearaddition shall be provided to the thickness determined according to class requirements to achieve anequivalent lifetime.

2.2.7 If the propeller of azimuthing thruster is subjected to highly oblique inflow in transient conditionssuch as hard steering or crash stop by turning the thruster units , the propeller blades shall be strengthenedaccordingly, considering possible load limitations. Safety factors as required for low cycle fatigue apply.

2.2.8 Regarding devices for improving propulsion efficiency, the rules for classification of ships Pt.3 Hull,shall be observed.

2.3 Pitch control mechanism and propeller hub

2.3.1 Mechanical components of a pitch control system and propeller hub shall be able to withstand thestatic loads with the safety factor against yield as specified in Table 7.

Table 7 Minimum safety factors for static strength of propeller hub, pitch mechanism and bladefitting mechanism

Load condition Required safety factor

Load transmitted when two of the blades are prevented from pitching (servo force acting ontwo blades) 1.0

Load transmitted when a propeller blade is exposed to maximum hydrodynamic load 2.0

Load corresponding to maximum servo pressure for strengthening the servo cylinder 2.0

Load corresponding to maximum servo pressure, with the load evenly distributed on allblades 1.3



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Guidance note:The latter load case is dimensioning for push-pull rods.


2.3.2 Safety factors for static load conditions reflect the risk and criticality related to the specified loadconditions, as well as the expected prediction quality of the acting loads. The minimum safety factors shallbe against yielding, and shall be applied on acting load. Local geometrical stress concentrations may beneglected. Stresses referred to are equivalent stresses. It is provided that stresses are predicted according togood engineering practice.As an alternative to check static strength against yielding, FE analysis may be carried out to documentdegree of plastification.When plastic deformations are included, applying the safety factors given in Table7, the static strength is considered satisfactory when the component remains within the specified designtolerances.

2.3.3 Maximum servo force (servo pressure corresponding to set point to safety valve) shall be applied in thecalculations. Guide pin is assumed to be located in the most critical position.

2.3.4 Unless the propeller is intended for auxiliary purposes only, fatigue strength of pitch mechanism andpropeller hub shall be considered taking the load conditions specified in Table 8 into account:

Table 8 Minimum safety factors for fatigue strength of propeller hub and pitch mechanism

Required safety factorLoad condition

Analytic method FE model

Start and stop of propeller 1.5 1.3

Change of pitch setting in normal operating condition 1.5 1.3

Rotational load variation of propeller in normal, aheadoperation (for propellers intended for propulsion only). 1.5 1.3

2.3.5 Fatigue strength related to each load condition may be calculated separately.

2.3.6 Applied dynamic loads, and the corresponding number of cycles, shall be as realistic as possible.Assumptions made shall in total be on the conservative side. Each of the load conditions described aboveshall be represented by a dynamic load and an associated number of load cycles, chosen as realistically aspossible.Minimum safety factors are given in Table 8, and shall be applied on acting dynamic loads versus fatiguestrength of material. These safety factors reflect the risk and criticality related to the specified loadconditions, as well as the expected prediction quality of acting loads, corresponding stresses and fatiguestrength of material. If significant simplifications and assumptions are made, these shall be such that thefatigue calculation result is on the conservative side.

2.3.7 Influence of stress concentrations shall be taken into account in fatigue calculation. Stresses referredto shall be principal stresses. It is presumed that stresses and fatigue strength are predicted according togood engineering practice.

2.3.8 The design shall be such that reasonably low stress concentrations are ensured.

2.3.9 For shrink fitted propellers, hub thickness shall be sufficient to avoid stresses from the dynamic loadingof propeller blades influencing significantly on the shrink fit and vice versa.



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Guidance note:In order to provide the above statement a hub thickness in way of propeller blade corresponding to 70% of the required thicknessof the propeller blade root section is considered sufficient.


2.3.10 The degree of filtration of hydraulic oil shall correspond to maximum allowable particle size in thesystem or better. In addition, the selection and arrangement of filters shall provide for an uninterruptedsupply with filtered oil, also during filter cleaning or exchange.

Guidance note:Specification of a pressure filter for maintaining suitable fluid cleanliness may be 16/14/11 according to ISO 4406:1999 and β6-7 (c)= 200 according to ISO 16889:2008.


2.3.11 For general design requirements for piping and ancillary equipment such as pipes, pumps, filters andcoolers see Ch.6 and Ch.7, as found applicable.

2.3.12 If necessary for corrosion protection, a hub cap with sufficient strength to protect the shaft effectivelyfrom water ingress shall be fitted. If hub cap with fins are mounted any damage of the fins shall not harm theintegrity of the cap.

Guidance note:If the hub cap thickness is equal to or larger than the fin thickness, damage to the fins may be assumed not to harm the integrityof the hub cap.


2.4 Fitting of propeller blades to the hub

2.4.1 The pre-tension of the blade bolts, including the verification procedure, shall comply with the following:

— Pretension stress in the minimum section of the blade bolts shall be in the range of 50% to 70% of thebolt-material yield strength or maximum 56% of the tensile strength, whichever is the least.

— Pretension shall be sufficient to obtain the required safety factors as follows:

— friction forces are sufficient to prevent sliding of the propeller flange when two blades are preventedfrom pitching. If shear devices are fitted, the sum of friction and shear forces shall be considered

— a surface pressure between mating surfaces is maintained (i.e. bolts maintain a prestress) in allpermissible operating conditions,

— any permissible operating condition shall not lead to yielding of bolt materials..

2.4.2 High cycle dynamic stress amplitudes in the minimum thread section of the blade bolts for propellersintended for propulsion shall fulfil the following criterion for normal, ahead operation:

where:

S = safety factor, see Table 8σA = dynamic stress amplitudeU = allowable nominal stress amplitude in the threaded area, 35 N/mm2 for machined threads and 60

N/mm2 for rolled threads.



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2.4.3 Other means of propeller blade fitting mechanisms will be considered and handled on a case-by-casebasis in agreement with the Society.

3 Inspection and testing

3.1 General

3.1.1 Blade bolt pre-tensioning shall be carried out in the presence of a surveyor.

3.1.2 All tests and inspections in [3.1.4] to [3.1.7] shall be carried out in the presence of a surveyor.

3.1.3 For controllable pitch propellers, all connections shall be properly sealed.

3.1.4 For controllable pitch propellers intended for propulsion, the following pitch settings shall, as aminimum, be properly marked on the hub and blade flange:

— pitch at 70% radius is zero— maximum pitch ahead (pitch limited by mechanical pitch stopper)— maximum pitch astern (pitch limited by mechanical pitch stopper).

The correctness of pitch marks and the mechanical feedback of pitch setting shall be verified by the Society.

3.1.5 The function of the pitch stoppers shall be demonstrated. If pitch stoppers are located outside of thehub, it shall be verified by the Society that maximum travel in each direction is less than inside the propellerhub.

3.1.6 After assembly, the complete servo system shall be properly flushed.

3.1.7 The complete controllable pitch propeller system shall be function tested and pressure tested asfollows:

— hydraulic pitch control to 1.5 times design pressure— tightness of propeller subject to 1 bar.

3.1.8 For hub caps serving as corrosion protection a tightness test shall be carried out.

3.1.9 The propeller blades shall be manufactured according to the specified tolerance class (ISO 484).As a minimum, verification of the following is required:

— surface finish— pitch (local and mean pitch)— thickness and length of blade sections— form of blade sections— location of blades, reference line and blade contour— balancing (see also [4.1])— for propellers running in nozzle or tunnel:

— extreme radius of blades (for controllable pitch propellers with outer section at zero pitch).

See also [2.1.4].For verification of blade edge thickness for ice classed propellers, see also Pt.6 Ch.6.



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Guidance note:Verification of blade section form may include the use of edge templates as specified for manufacturing tolerance classes S and I inISO 484.Equivalent methods can be accepted, for instance the use of multi-axial milling machines, which have proven to be capable ofproducing the specified geometry with such an accuracy that only a slight grinding is necessary to obtain the specified surfacefinish.


3.2 Inspection and testing of parts

3.2.1 Certificates shall be provided as required in Table 2.

3.2.2 With respect to non-destructive testing for detection of surface defects, the following acceptancecriteria apply:

— for propeller blades and hubs, the criteria given in Pt.2 Ch.2 Sec.8 and Pt.2 Ch.2 Sec.11 apply— no defects are accepted in highly stressed areas of components in the pitching mechanism.

4 Workshop testing

4.1 General

4.1.1 The complete propeller shall be statically balanced in accordance with specified ISO 484 tolerance class(or equivalent) in presence of a surveyor. Dynamic balancing shall be carried out for propulsion propellerswith tip speed exceeding 60 m/s. The manufacturer shall demonstrate that the assembled propeller shall bewithin the specified limits.

Guidance note:For built-up propellers, the required static balancing may be replaced by an individual control of blade weight and gravity centreposition.


5 Control and monitoring

5.1 General

5.1.1 For controllable pitch propellers, control and monitoring systems shall comply with the requirements ofCh.9.

5.1.2 Pitch adjustment shall not be used as load control system of prime mover, unless the propeller systemis especially designed for this purpose.

5.1.3 A local control stand for pitch control shall be arranged.

5.1.4 Instrumentation and alarms shall be provided according to Table 9, if not otherwise approved.



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Table 9 Control and monitoring of propeller

System/Item

Gr 1Indication

alarm

load reduction

Gr 2Automaticstart of

standby pumpwith alarm

Gr 3Shutdownwith alarm Comments

1.0 Pitch, speed and direction of rotation

Propeller rotational speed IR

Direction of rotation forreversible propellers IR

Propeller pitch for CP-propellers IL, IR

For propulsion, the following pitchsettings shall be marked on the localpitch indicator:

— Mechanical pitch limits aheadand astern, pitch at full aheadrunning, maximum astern pitchand pitch at zero thrust.

2.0 Servo oil for CP-propeller

Pressure IL, IR, LA AS1) The indicators shall be able to showsudden peaks in servo pressure.

Level IL, LA

Differential pressure over filter HA 2)

Gr 1 = Sensor(s) for indication, alarm, load reduction (common sensor permitted but with different set points andalarm shall be activated before any load reduction)

Gr 2 = Sensor for automatic start of standby pump

Gr 3 = Sensor for shutdown

IL = Local indication (presentation of values), in vicinity of the monitored component

IR = Remote indication (presentation of values), in engine control room or another centralized control station suchas the local platform/manoeuvring console

A = Alarm activated for logical value

LA = Alarm for low value

HA = Alarm for high value

AS = Automatic start of standby pump with corresponding alarm

LR = Load reduction, either manual or automatic, with corresponding alarm, either slow down (r/min reduction) oralternative means of load reduction (e.g. pitch reduction), whichever is relevant

SH = Shut down with corresponding alarm. May be manually (request for shut down) or automatically executed ifnot explicitly stated above.

For definitions of load reduction (LR) and shut down (SH), see Ch.1.

1) To be provided when standby pump is required, see [6.3.1].2) Applies only to propulsion propellers.



DNV AS

6 Arrangement

6.1 General

6.1.1 Bolts and nuts shall be properly secured, see [8.2.3].

6.2 Arrangement of propeller

6.2.1 The arrangement and design of the propeller shall be such that satisfactory performance is maintainedunder all operating conditions.

6.2.2 The arrangement of attached free-wheeling propellers shall be especially considered.

6.3 Hydraulic system for pitch control

6.3.1 Unless the propeller is intended for auxiliary purposes only, for single propulsion plants where thepitch-control mechanism is operated hydraulically, at least two mutually independent, power-driven pumpsets shall be installed.

6.3.2 For general requirements with respect to hydraulic systems, see Ch.6 Sec.5 [8.1].

7 Vibration

7.1 General

7.1.1 Not applicable.

8 Installation inspection

8.1 General

8.1.1 Installation of external components shall be carried out according to the maker’s specifications.

8.2 Fitting of propeller and propeller blades

8.2.1 For fitting of propeller, see Ch.4 Sec.1.

8.2.2 For blade bolt pre-tensioning, see [3.1.1].

8.2.3 The surveyor shall verify that bolts and nuts are properly secured. In case bolts are fixed by welding, itshall be verified that only regions with low stress levels are affected.

8.3 Pitch marking

8.3.1 For pitch marking, see [3.1.4].



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8.4 Hydraulic piping

8.4.1 Pipes shall have a suitable location and be properly clamped. Inspection and testing shall be possible.

8.4.2 The hydraulic system shall be flushed after assembly to a degree of cleanliness as specified by themaker.

8.4.3 System hydraulic oil shall be in accordance with maker's specification.

9 Shipboard testing

9.1 Sea trial

9.1.1 For controllable pitch propellers, the pitch function and the servo pressure shall be demonstrated tothe satisfaction of the surveyor. Also the function of the local pitch control shall be demonstrated, and thecorrectness of local pitch indicator shall be verified.

9.1.2 Unless the propeller is intended for auxiliary purposes only, the pitch behaviour with inactive servo(zero servo pressure) shall be demonstrated to the surveyor during sea trial.

9.1.3 The performance of the propeller shall be tested at both full ahead operation and full astern operation.For fixed pitch propellers reversing shall be tested at maximum permissible astern r/min. For controllablepitch propellers reversing shall be tested at maximum astern pitch of maximum permissible r/min.

9.1.4 For controllable pitch propellers, the function and setting of the safety valve shall be demonstrated tothe satisfaction of the surveyor.

9.1.5 The filter for the servo oil shall be inspected after the sea trial.



DNV AS

SECTION 2 WATER JETS

1 General

1.1 Application

1.1.1 The rules in this section apply to axial water jets intended for main propulsion and steering for alltypes of vessels.

1.1.2 Ch.2 describes all general requirements for rotating machinery and forms the basis for all sections inCh.3, Ch.4, Ch.5 and Ch.10.

1.1.3 Water jet units with main steering function are also regarded as steering gear for the vessel.

1.1.4 Water jet units for auxiliary steering purposes (i.e. not for propulsion) are only subject to classificationafter special consideration.

1.2 Documentation

1.2.1 The manufacturer shall submit the documentation required by Table 1. The documentation shall bereviewed by the Society as a part of the certification contract.

Table 1 Documentation requirements


C020 - Assembly or arrangementdrawing Including cross section FI

C040 - Design analysis Impeller thrust, vessel thrust andmaximum reversing forces at crash stop FI

Z100 - SpecificationWater jet pump characteristic, withoperation limits including cavitation limits,see limit as for Table 5

FIWaterjet, fixed;Waterjet, variable

Z100 - Specification

Normal operating parameters that definethe permissible operating conditions, suchas thrust, impeller speed, vessel speed,impeller speed. versus vessel speed, seelimitations in Table 5

FI

Z261 - Test report Non-destructive testing (NDT) FI

C030 - Detailed drawingInput shaft and impeller shaft shallbe documented according to rules forshafting

AP

C020 - Assembly or arrangementdrawing Bearing arrangement with particulars AP

C040 - Design analysis Calculated lifetime of roller bearings AP

Shafting

C030 - Detailed drawing Seal box, if water lubricated FI



DNV AS


C030 - Detailed drawingAll bolt connections carrying thrust ortorque, specification of bolt material andtightening procedure (bolt pre-stress)

AP

C030 - Detailed drawing Including NDT specification FIImpeller

C040 - Design analysis Impeller blade strength calculations FI, R

C030 - Detailed drawing With guide vanes FIStator housing

C040 - Design analysis Strength calculations FI, R

C030 – Detail drawing Including bolting APStern flange

C040 – Design analysis Strength calculation FI

C020 - Assembly or arrangementdrawing Including water inlet ducting FI

C030 - Detailed drawing Cross section of unit. FI

C040 - Design analysis Water inlet ducting, hydrodynamic FI

Waterjet casing

C040 - Design analysis Housing strength calculations, see [2.2] FI, R

C020 - Assembly or arrangementdrawing Steering arrangement AP

C040 - Design analysis Strength calculation of the steering andreversing mechanism APReversing arrangement;

Steering arrangement

S042 - Hydraulic control diagram Including relief valve setting and alarm listwith set points AP

Reversing deflectoractuator C030 - Detail drawing AP

Steering deflectoractuator C030 - Detail drawing AP

Control and monitoringsystem

I200 - Control and monitoring systemdocumentation According to Ch.9 AP

AP = For approval; FI = For information; R = On request

1.2.2 For general requirements for documentation, including definition of the info codes, see DNV-CG-0550Sec.6.

1.2.3 For a full definition of the documentation types, see DNV-CG-0550 Sec.5.

1.3 Required compliance documentation

1.3.1 Water jet parts, semi-products or materials shall have compliance documents according to Table 2 andtested according to Table 3 and [3.2].

1.3.2 All piping systems shall be properly flushed, in accordance with the manufacturer’s specification. Thisshall be documented by a work certificate.



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Table 2 Certification required



Waterjet PC Society

PC Society Required if manufactured by sub-supplier

MD ManufacturerImpeller

PTR Manufacturer Balancing - See [3.2.4]

Stator housing MD Manufacturer

Impeller housing MD Manufacturer

Shafting MD Manufacturer As required in Ch.4 Sec.1

PC Society Required if manufactured by sub-supplierHydraulic actuators for

reversingMD Manufacturer

MDOther reversing components

NDTManufacturer

PC Society Required if manufactured by sub-supplierHydraulic actuators for

steeringMC Society

Other steering components MD Manufacturer

Bolts MTR Manufacturer

Ducting MD Manufacturer If delivered integral with the waterjet

Control and monitoringsystem PC Society

*Unless otherwise specified the compliance standard is the Society rules.

1.3.3 For general compliance documentation requirements, see DNV-CG-0550 Sec.4.

1.3.4 For a definition of the compliance document types, see DNV-CG-0550 Sec.3.

1.3.5 The surveyor shall do visual inspection of parts. Visual inspection shall include random dimensionalcheck with emphasis on critical dimensions, tolerances and stress raisers.Manufacturer’s measurement report shall be presented for main items and shall be available upon request forminor components.Manufacturer’s survey report shall be available upon request.



DNV AS


Ultra-sonic orX-ray testing

Surface crackdetection 3) Pressure testing Dimensional

inspectionVisual

inspection Other

Impeller Manufacturer Manufacturer Society Manufacturer1)

Statorhousing Manufacturer4) Manufacturer Manufacturer Society

Impellerhousing Manufacturer4) Manufacturer Manufacturer Society

Shafting According to Ch.4 Sec.1

Hydraulicactuators forreversing andsteering 5)

U-S or surface crack detection(manufacturer)4)

Society ormanufacturer2)

Othersteering andreversingcomponents

Manufacturer4) Manufacturer

Bolts

Ducting whendeliveredintegral withthe water jet

Manufacturer Manufacturer Society

1) See [3.2.4].2) Society for steering hydraulic actuators, manufacturer for reversing hydraulic actuators.3) Crack detection in final condition.4) NDT of welds upon request.5) Hydraulic actuator includes cylinder, rod, cylinder end eye and rod end eye.

1.4 Definitions

1.4.1 The following definitions in Table 4 are used in this section.

Table 4 Definitions

Term Definition

ductingwater streaming along the vessel’s bottom and flows into a duct, leading the water to thewater jet. The duct forms an integral part of the vessel hull. It is normally manufactured at thebuilder

hydraulic actuators used for either steering or reversing as the driving force that impose the reversing bucket oracts on the steering nozzle to create a change in the water flow direction

impeller the rotating hub with blades. The impeller is connected to the shaft. The impeller is usually castin one piece. Alternatively, the blades are welded onto the hub

impeller housing the water jet casing surrounding the impeller



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Term Definition

reversing bucket

for reversing purposes, the water jet incorporates components that can force its entry intothe water flow thereby turning the water jet discharge to be thrown somewhat forwards. Thiscreates a reversing force that acts on the vessel. The flow is either thrown forwards in an angledirected below the vessel, or to both of the sides of the water jet. The components used forthis purpose is denoted a bucket

stator housingby leading the water flow through a row of stationary vanes downstream of the impeller, theswirl added to the water by the impeller is reduced, and the longitudinal speed of the waterflow is increased. The vanes are usually formed as an integral part of the water jet housing

steering nozzlethe water flow is lead through a passageway that can be tilted horizontally in relation to thevessel's longitudinal axis, thereby changing the direction of the water jet flow. This creates aturning moment used for steering the vessel

2 Design

2.1 General

2.1.1 For general design principles for machinery, see Sec.1 [2].

2.1.2 The water jet unit shall be capable of withstanding the loads imposed by all permissible operatingmodes, including the condition when the inlet of the suction is blocked.

2.1.3 The stresses in water jet components shall be considered based on loads due to the worst permissibleoperating conditions, taking into account:

— hydrodynamic loads, including varying hydrodynamic loads due to water flow disturbances introduced e.g.by the ducting or hull

— vessel accelerations versus water jet r/min.

2.1.4 Harmful impeller cavitation shall not occur when operating at full design speed on a straight course andat designated trim, giving the designed water head above the water intake.

Guidance note:Harmful cavitation in this context is that cavitation which shall reduce shafting system and water jet component lifetime byintroducing vibration or impeller erosion.The water jet may be exposed to operating conditions outside the intended design. Such situations may occur for instancedue to increased vessel weight, increased hull resistance, vessel operating at deeper waters etc. In situations where operationexceeds the design premises, harmful impeller cavitation may occur as a consequence of abnormal water jet flow conditions. Thisphenomenon has showed to be of increasing importance with increasing water jet size.To combat this, the water jet should be designed with reasonable margin for cavitation, and care should be taken to avoid vesseloverweight due to e.g. reasons mentioned in the above. The bigger the water jets are the more important this advice become.


2.1.5 The water jet units shall be provided with inspection facilities for inspection of the shaft and impeller.

2.2 Design of components

2.2.1 The dimensions of the shafts and the shafting components, including bearings, shall comply with therequirements in Ch.4 Sec.1.



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2.2.2 The impeller housing and stator housing shall be designed against fatigue, considering impeller pulsesand other flow pulses.

2.2.3 Steering and reversing mechanisms shall be designed taking into account the worst permissibleoperational conditions.

2.2.4 The materials used in the hydraulic actuators shall be suitable for the expected environmentalconditions.

2.2.5 Hydraulic actuators for steering shall comply with the requirements given in the Ch.10.

2.2.6 Hydraulic actuators for reversing shall comply with the requirements given in Ch.6 Sec.5 [8]. However,if the hydraulic system for the reversing actuators is the same as for the steering system, the design and testpressure for the reversing actuators shall be the same as for the steering actuators. Higher nominal stressesmay be accepted for the reversing actuator.

2.2.7 The critical details of the duct and connections to the hull structure shall be designed against extremeloads occurring during crash stop and fatigue considerations related to reversing, steering and impellerpulses.


3.1 General

3.1.1 The principles of manufacturing survey arrangements (MSA) are described in Pt.1 Ch.1 Sec.4.

3.1.2 Ancillaries not covered by Table 2 or Table 3 and are integrated as part of the water jet, shall bechecked as found relevant by the waterjet manufacturer.

3.1.3 Welding procedures shall be qualified according to a recognised standard or Pt.2.

3.2 Testing and inspection of parts

3.2.1 The inspection and testing described in the following are complementary to Table 3.

3.2.2 The visual inspections by the Society shall include random dimensional check of vital areas such asflange transition radius, bolt holes etc., in addition to the main overall dimensions.

3.2.3 Particulars concerning ducting inspections are stated in [8.1.5].

3.2.4 The impeller shall be statically balanced.Guidance note:VDI standard no. 2060 Quality class 6.3 or ISO 1940/1 Balance Guide G6.3 may be used as reference.


3.3 Assembling

3.3.1 For fitting of the impeller to the shaft, see Ch.4 Sec.1 [2.3] to Ch.4 Sec.1 [2.7].



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4 Workshop testing

4.1 General

4.1.1 Not applicable.

5 Control, alarm, safety functions and indications

5.1 General

5.1.1 Systems shall comply with the requirements in Ch.9.

5.2 Monitoring and bridge control

5.2.1 The monitoring of water jets (for propulsion) shall be in accordance with Table 5 in regard to:indications, alarms and requests for slowdown.

Table 5 Control and monitoring of water jets

System/Item

Gr 1Indication

alarm

load reduction

Gr 2Automatic

start of stand-by pumpwith alarm

Gr 3Shut downwith alarm Comment

1.0 Steering

Loss of steering and reversingsignal A, LR Request for slow down

2.0 Hydraulic oil

Pressure IR, LA, LR Request for slow down

Level in supply tank IL, LA

3.0 Lubricating oil

Temperature IR, HA

Pressure (if forced lubrication) IR, LA, LR Request for slow down

Level in oil tank (if provided) IL, LA

4.0 Operational limitations1)

The ratio impeller r.p.m versusvessel speed IR, HA, LR Request for slow down

Maximum permissible vesselacceleration exceeded Indication on bridge



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System/Item

Gr 1Indication

alarm

load reduction

Gr 2Automatic












LR = Load reduction, either manual or automatic, with corresponding alarm, either slow down (r/min reduction) oralternative means of load reduction (e. g. pitch reduction), whichever is relevant


For definitions of load reduction (LR) and shut down (SH), see Ch.1.

1) These requirements are only valid for water jets with inlet diameter in excess of 1 000 mm.

5.2.2 Monitoring and bridge control shall also be in compliance with Ch.9 and Ch.10 Sec.1 [5.5] to Ch.10Sec.1 [5.7].

5.2.3 Frequent corrections in the steering control system, when the vessel is on straight course, shall beavoided if practicable.

Guidance note:The actual corrections should be read preferably by monitoring the control signal. Alternatively, direct measurements onmechanical feedback device from the water jet can be used.


6 Arrangement

6.1 General

6.1.1 The installation and arrangement of the water jet unit with auxiliaries shall comply with themanufacturer’s specification.

6.1.2 Ship external parts of the water jet shall be protected by guard rails or other suitable means.



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7 Vibration

7.1 General

7.1.1 For requirements concerning whirling calculations and shaft alignment specification, see Ch.2.

7.1.2 For requirements concerning torsional vibration calculations for water jets, see Ch.2.

8 Installation survey

8.1 Surveys

8.1.1 The fastening of the water jet to the hull and the structural strengthening around the water jet unitwith ducting shall be carried out in agreement with the approved drawings.Foundation of water jet is subject to survey by Society (see Ch.2 Sec.6).

8.1.2 Impeller clearances shall be checked after installation and shaft alignment and shall be in accordancewith the manufacturer’s specification.

8.1.3 Normal procedures for shafting apply, see Ch.4 Sec.1 [7].

8.1.4 Thrust bearing axial clearances after installation shall be verified to be in accordance with themanufacturer specification, unless verified during assembly of the water jet.

8.1.5 The ducting shall be manufactured in accordance with drawings and specifications from the waterjet designer. The surfaces shall be smooth and free from sharp edges or buckling that could give raise toturbulence in the water flow and thereby adversely affect water jet operating conditions.

Guidance note:Great care should be taken in assuring that the ducting dimensions agree with the water jet designer’s drawings. The ductingdesigner should be consulted for use of possible dimensional checking equipment, such as templates especially made for thatpurpose.


8.1.6 Pressure testing of piping shall be done according to Ch.6.

9 Shipboard testing

9.1 General

9.1.1 For general requirements related to the testing of control and monitoring, see Ch.9.For testing of steering gear, Ch.10 Sec.1 [8] applies.

9.1.2 Final acceptance of the control system is dependent upon satisfactory results of the harbour testingand the final sea trial, as specified in items [9.1.3], [9.1.4] and [9.1.5].

9.1.3 Attention shall be paid to combinations of operational functions. Testing of all combinations of functionsshall be carried out.



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9.1.4 Indication and alarm (if applicable) of operation outside the specified operation limits shall be checked.This applies to acceleration as well as impeller speed versus vessel speed.

9.1.5 The water jet speed versus vessel speed shall be noted and plotted against the manufacturersoperational curves when inlet diameter exceeds 1000 mm. The surveyor shall verify the correct reading ofvalues, and the results shall be submitted to the approval centre after completion of test.



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SECTION 3 PODDED AND GEARED THRUSTERS

1 General

1.1 IntroductionPropulsion thrusters are often a part of a large and complex system serving both propulsion and steering,which requires a different safety approach with respect to design and control than a conventional propulsionand steering arrangements. These rules have taken this into consideration, in order to provide specific andrelevant requirements.The rules for steering gear, see Ch.10, are not intended for directional control of thrusters. DNV has thereforeimplemented relevant interpretations of requirements from SOLAS and Ch.10 to provide more relevant rules.

1.2 ObjectiveThe objective of these rules is to provide requirements for design and operability of thrusters, independent oftype, power source and steering method.

1.3 ScopeThis section gives design and test requirements for propulsion, dynamic positioning and manoeuveringthrusters, including control and safety functions.For manoeuvring thrusters with power of 300 kW and below, the scope of these rules is limited to control,alarm, safety functions and indication, see [3.8], and barrier to sea, see [2.3.4] and [3.2.5].For units using a pump or impeller to generate thrust, see Sec.2.

1.4 Application1.4.1 PropulsorsThe rules apply to thruster plants intended for:

— propulsion— propulsion and steering— dynamic positioning— manoeuvring.

1.4.2 Alternative designThrusters of a design not directly meeting the prescriptive requirements of this section, may be acceptedwith basis in Pt.1 Ch.1 Sec.1 [2.5.9].

1.4.3 Requirements in other parts of the rulesAdditional class notations as listed below may impose additional requirements to thruster units and/orarrangements.

— Ice, vessel strengthened for operation in ice infested waters, see Pt.6 Ch.6— PC, vessel intended for navigation in ice infested polar waters, see Pt.6 Ch.6— Icebreaker, vessel purpose ice breaking, see Pt.5 Ch.10 Sec.10— Naval and Naval support, naval flagged vessels administered by a national naval administration, seePt.5 Ch.13

— RP, redundant propulsion, see Pt.6 Ch.2 Sec.7— SRTP, safe return to port, see Pt.6 Ch.2 Sec.11— DYNPOS and DPS, dynamic positioning system, see Pt.6 Ch.3 Sec.1 and Pt.6 Ch.3 Sec.2.



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Guidance note:Vessels classed according to rule books other than DNV-RU-SHIP may refer to these rules, with possible amendments.


1.4.4 Steering gearThe requirements in [3.4] are applicable to steering gear for azimuth thrusters.

1.4.5 Electric propulsionFor requirements to electric motor as drive for podded and geared thrusters, see Ch.8 Sec.12.

1.5 Definitions and symbols1.5.1 Definitions relevant for thrusters

Table 1 Definitions - thruster application and thruster types

Term Definition

thruster assembled unit equipped with a propeller in order to produce thrust and is considered to be thecomplete assembly: from the propeller with nozzle (if applicable) to the input shaft at the uppergear or slip ring unit (if applicable)It may also include various support systems.

propulsion thruster thruster that is assigned to propulsion of the vessel

manoeuvring thruster thruster for purposes other than propulsion of the vessel 1)

dynamic positioningthruster

propulsion or manoeuvering thruster that is a part of a dynamic positioning system on board avessel with a dynamic positioning class notation, see Pt.6 Ch.3 Sec.2 and Pt.6 Ch.3 Sec.1

geared thruster thruster with a lower gear, alternatively both lower and upper gears, connected to an externaldriver

podded thruster thruster with the prime mover directly attached to the propeller shaft(often referred to as 'pod' or 'podded propulsor')

azimuth thruster thruster rotating around its vertical axis and capable of providing steering capability by omni-directional thrust

tunnel thruster thruster mounted in a tunnel providing lateral thrust for the vessel

cycloidal thruster thruster rotating around its vertical axis with vertical propeller bladesThe blades produce force (thrust or lift) in any direction normal to the axis of rotation.

rim thruster podded thruster where propeller and tunnel or nozzle are used as rotor and stator for thepropulsion motorThe motor's air gap is water filled.

1) This was previously referred to as auxiliary thruster.

Table 2 Definitions - steering

Term Definition

auxiliary steering gearequipment other than any part of the main steering gear necessary to steer the ship in theevent of failure of the main steering gear, but not including the tiller, quadrant or componentsserving the same purpose 1)



DNV AS

Term Definition

declared steering anglelimits

operational limits in terms of maximum steering angle, or equivalent, according tomanufacturer's guidelines for safe operation, also taking into account the vessel's speed orpropeller torque/speed or other limitation and the ship designer's consideration of ship dynamicstability 2)

design pressure maximum pressure for which the hydraulic actuator is designed

design steering torque maximum torque for which the steering gear is designed. Corresponding to design pressure forhydraulic steering 4)

main steering gearmachinery, rudder actuators, steering gear, power units and ancillary equipment and themeans of applying torque to the rudder stock (e.g. tiller or quadrant) necessary for providingmovement of the rudder for the purpose of steering the ship under normal service conditions 1)

maximum workingpressure

maximum obtained pressure in the hydraulic system during the SOLAS steering gear trial testin case of hydraulic steering gear 5)

maximum workingsteering torque highest steering torque obtained at trial during the SOLAS steering gear trial test 4)

neutral positioncentre position or other position with manageable steering loads when going aheadNeutral position is used to lock a failed steering gear in a position suitable for operation ofvessel, but with loads manageable for a failed steering gear6).

slewing gearmechanical gear transmission used in azimuth steering gearThe slewing gear wheel is mounted on the azimuthing unit, while the pinions are driven by thesteering actuators 7)

steering actuatingsystem

system consisting of steering gear power unit, steering actuator, and steering hydraulic pipingsystem as applicable 8)

steering actuator mechanical system giving torque to the slewing gear wheel including all components in themechanical transmission 9)

steering gear steering actuating systems and slewing gear wheel 10)

steering gear powerunit

system generating power to a steering gear actuator 11) 12)

— in the case of electric steering gear, an electric motor and its associated electricalequipment;

— in the case of electrohydraulic steering gear, an electric motor and its associated electricalequipment and connected pump;

— in the case of other hydraulic steering gear, a driving engine and connected pump

steering gear controlsystem

equipment by which orders are transmitted from the navigating bridge to the steeringgear power units. Steering gear control systems may comprise transmitters, receivers,programmable electronic units, motor controllers, frequency converters and cables 4)

steering hydraulicpiping all piping components in a hydraulic steering gear, including relief valves 9)

steering-propulsion unit unit combining propulsion and steering functions 4)

steering system in this context to be understood as an azimuth thruster including its supporting systems 2)



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Term Definition

1) SOLAS Part A Reg.3. Term not applied in this rule section, as main and auxiliary duties are covered by redundancy2) Defined in IACS UI SC242, but complete definition is not implemented as it is seen as design requirement and not a

definition. Definition in UI SC242 may also prevent an effective crash stop procedure3) DNV definition based on requirements in SOLAS Part C Reg.294) DNV definition5) DNV definition, it is extended from rudder turning test in SOLAS Part C reg.29.3.26) DNV definition, it is extended versus MSC circ 1053 as it allows positions other than in center line +- 1 deg7) DNV definition, limitation of general industrial terms8) DNV definition, not equal to definition in SOLAS Ch.II-I Pt.A Reg.39) DNV definition, based on SOLAS and IACS applications10) DNV definition, SOLAS reg.29 is named steering gear but it is not defined. Definition is derived from main and

auxiliary steering gear11) SOLAS definition of "power actuating system" SOLAS Ch.II-I Pt.A Reg.3 definitions, IACS UR-M4212) See Figure 113) DNV definition, not equal to SOLAS definition as new technology is implemented such as frequency converters14) DNV definition, introduced and applied several places in IACS UI SC242 but not defined

Figure 1 Hydraulic and electrical steering gears

Table 3 Definitions - general

Term Definition

azimuthing unitassembled unit being turned around during steeringNormally consisting of steering column, underwater housing, propeller and slewing gear wheel.

housing all structural elements both in inboard steering gear and in underwater units

loaded in the context of this rule section it is used to identify components or structures where static ordynamic stresses shall to be taken into consideration



DNV AS

Term Definition

maximum aheadservice speed

maximum forward vessel speed at maximum nominal shaft speed and corresponding driverrating in service at the deepest seagoing draught

maximum astern speed estimated speed which the ship can attain at the designed maximum astern power at thedeepest seagoing draught

propulsion line mechanical shafting transmission, used on both manoeuvering and propulsion thrusters

steering gear unitassembly for control of thrust directionThis is often the fixed unit connected to hull and to the azimuthing unit

thruster supportsystems

systems and components not part of azimuthing or steering gear unitTypical lubrication oil support, cooling systems, electrical drives, cabinets, etc.

1.6 Documentation1.6.1 Documentation requirementsA full definition of the documentation types is given by DNV-CG-0550 Sec.5. General documentationrequirements including info codes are given by DNV-CG-0550 Sec.6.

1.6.2 Documents from builderBuilder shall submit documentation as required by Table 4.

Table 4 Documentation requirements - builder

Object Document type Additional description Info

Z250 - Procedure

Operation instruction poster for control and steering ofthe thruster, including emergency operation. Shall bedisplayed on the navigation bridge and in the steering gearcompartment. Steering gear SOLAS poster, see SOLAS Ch.VReg.26.

APPropulsionthruster

Z030 - Arrangement plan Thruster room arrangement. FI

Z030 - Arrangement plan Local hull structure, thruster unit, including driver andintermediate shafting. FI

H053 - Foundation andsupporting structure drawing Including seals. AP

I210 - Integration plan FI, L

Z253 - Test procedure for quayand sea trial FI, L

Thruster

Z263 - Report from quay and seatrial FI, L

1.6.3 Documents from manufacturer for design assessmentManufacturers shall submit documentation as required by Table 5 to Table 11 as applicable.



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Table 5 Documentation requirements - general


Z161 - Operation manual Including operational modes and failure handling. FIPropulsionthruster Z051 - Design basis Loads for the defined operational modes. FI

Z110 - Data sheet DNV form THR 401. FI

C020 - Assembly or arrangementdrawing Main dimensions. FI

C020 - Assembly or arrangementdrawing

Sectional view with description of surfaces and spaces withrespect to environment, exposed to sea, oil filled, air filled,etc.

FI

Z050 - Design philosophy Bearing (electrical isolation) and earthing of components. FI

Thruster

Z163 - Maintenance manual For the complete thruster unit with associated auxiliarysystems. FI

S030 - Capacity analysis Flow and pressure. FI

S042 - Hydraulic control diagram Including alarm and indicator set points. AP

Hydraulicpowersystems forsteering,retractingandoperatingcontrollablepitchpropeller

Z060 - Functional description Hydraulic circuit. FI, R

Electric components, e.g. motors, frequency converters, slip-ring units shall be documented as required inCh.8.

Table 6 Documentation requirements - housing


C030 - Detailed drawing Machining and welding. AP

C030 - Detailed drawing Propeller nozzle. AP

C040 - Design analysis Finite element analysis of complete housing with identifiedstress levels. FI, R

Structuralparts

M150 - Non-destructive testing(NDT) plan FI

C040 - Design analysis Loaded bolted connections. FIBoltedconnections C030 - Detailed drawing Bolts exceeding M39 and associated shear pins. AP

Table 7 Documentation requirements - propulsion line


ShaftingC020 - Assembly or arrangementdrawing Including mass elastic system. FI



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https://eformsconnect.dnv.com/forms/5032



Drawings of the shafts, liners and rigid couplings.The drawings shall show clearly all details, such as:

— fillets— keyways— radial holes— slots— surface roughness— shrinkage amount— contact between tapered parts— pull-up— bolt pretension— protection against corrosion.

AP

M010 - Material specification,metals AP

C040 - Design analysis Shaft strength and connections. FI

C020 - Assembly or arrangementdrawing Shaft brake/locking device arrangement. FI, R

C030 - Detailed drawing Propeller shaft seal arrangement if not type approved. AP

C020 - Assembly or arrangementdrawing Bearing arrangements. FI

C040 - Design analysis Applicable for roller bearings: bearing lifetime calculations. APBearings

Z100 - SpecificationApplicable for journal bearings: material, nominal surfacepressure and clearance tolerances in case of fluid filmbearings.

FI

Z110 - Data sheet DNV form 71.10a for gears in propulsion shafting. AP

C030 - Detailed drawing Pinions and wheels. AP

C040 - Design analysis

Calculation for each gear stage, documenting compliancewith Ch.4 Sec.2 [2.1]. The various data are explainedin class guideline DNV-CG-0036 and data sheet for gearcalculations, DNV form 71.10a.

APGearedthruster

M010 - Material specification,metals

Types of material and mechanical properties, cleanliness (ifmaterial of high cleanliness is used). AP

C040 - Design analysis Connection of stator to housing. FI

C040 - Design analysis Rotor assembly bolted connections. FI


Sectional drawing of electric motor, including:

— stator-to-housing connections— rotor-to-shaft connections— specified air gap with tolerances.

AP

Z250 - Procedure Exciter - connection and replacement plan in case of failure. FI

Poddedthruster

C070 - Permanent magnetmachine documentation See Ch.8 Sec.5 [3] and Ch.8 Sec.1 Table 2.



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Propellers shall be documented as required in Sec.1.Torsional vibration shall be documented as required in Ch.2 Sec.2.

Table 8 Documentation requirements - steering gear


Sectional view including all components from driving motorto connection between steering gear and thruster housing. FI

C020 - Assembly or arrangementdrawing Sectional view of high-speed gear box e.g. planetary gear, to

be included if applicable. FI

C030 - Detailed drawing Load transmitting parts. AP

Z060 - Functional description Azimuth brake and locking device, including maximumtorque. AP

Z265 - Calculation report Calculation of high-speed gear transmissions, e.g. planetarygear. AP, TA

Z110 - Data sheetParticulars steering gear motors: type (electric/hydraulic),maximum power, maximum speed, inertia and rating (forelectric motors).

FI

General

Z060 - Functional description Torque limitation device, if applicable, including specificationof setting value. FI, TA

Z110 - Data sheet DNV form 71.10a. AP

C030 - Detailed drawing Pinions and wheels. AP

C040 - Design analysis Conclusive analysis for dimensioning of slewing gear. FISlewinggear

M010 - Material Types of material and mechanical properties, cleanliness (ifmaterial of high cleanliness is used). AP

C020 - Assembly or arrangementdrawing Bearing arrangement. FI

Z265 - Calculation report Roller bearing lifetime. APAzimuthconnection

C020 - Assembly or arrangementdrawing Slewing seal system. AP

Electric equipment that is a part of the steering gear shall be documented as required in Ch.8 Sec.1 [2.2].

Table 9 Documentation requirements - support systems


Z060- Functional description Lubrication steering gear and azimuth bearings. FIThruster

S010 - Piping diagram (PD) Seal support systems, if applicable. FI

C040 - Design analysis Cooling system, description and heat balance. FI

S010 - Piping diagram (PD) Lubrication oil system including alarm and indicator setpoints. APPodded

thruster

Z060 - Functional description Lubrication system shaft bearings. FI



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S010 - Piping diagram (PD) Bilge system. AP

Z060 - Functional description Bilge system. FI

Table 10 Documentation requirements - special devices



C030 - Detailed drawing APRetractingdevices

C040 - Design analysis FI

Flexiblemounting

C020 - Assembly or arrangementdrawing Including sealing arrangement between thruster and hull. AP

Table 11 Documentation requirements - control and monitoring systems


Thruster, alltypes andapplications

I200 - Control and monitoringsystem documentation See Ch.9. AP

1.6.4 Documents for verification of manufacturingDocuments used as verification of the manufacturing process and products, shall be provided locally to theSociety's surveyor.

Table 12 Documentation requirements - manufacturing assessment


M0151 - Non-destructive testing(NDT) procedure FI, L

M0152 - Non-destructive testing(NDT) report FI, LHousing

M060 - Welding procedures(WPS) FI, L

1.6.5 Documents upon requestDocument requirements as listed in Table 5 to Table 12 are based on standard designs and technologies.Documents marked with an R in the info field are upon request and will only be requested when suchinformation is found necessary by the Society.Additional documentation may be requested, see Pt.1 Ch.1 Sec.1 [2.5.6], Pt.1 Ch.1 Sec.1 [2.5.10] and Pt.1Ch.1 Sec.1 [2.6.2]. This may typically be relevant for novel technology, new designs, new manufacturers orspecial applications. The request will be based on risk evaluation and service experience. Documents mayeither be for information or for approval.



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Table 13 Examples of documents which may be requested in special cases

Document type Additional description

Z080 - Reliability and availabilityanalysis

High level interdisciplinary analysis on a qualitative level with focus on fit for purposeand critical design elements.

Z265 - Calculation report Calculation of loads for the defined operational modes.

Z050 - Design philosophy

Operational (design) limitations such as, but not limited to:

— limitations in rotation of azimuth thrusters at high vessel speed— maximum speed for lowering and lifting of retractable units.

C040 - Design analysis Finite element analysis of structure identifying vibration modes and frequencies.

Z250 - Procedure Assembling and adjustment procedures regarding gear mesh contact.

Z071 - Failure mode and effectanalysis (FMEA) Complete steering gear, but also other arrangements as found relevant.

1.7 Required compliance documentation1.7.1 Product certificateThe complete thruster shall be delivered with compliance documents as required in Table 14 and Table 15 andbe tested and inspected as required in Table 19. Components and systems with requirements to certificationand testing described in other rule chapters are listed in Table 20.The compliance documents shall be based on the design approval in [2] and [3], the component certificationbased on workshop testing in [4] and relevant monitoring equipment in [3.8].Steering gear unit and azimuthing unit module shall have individual compliance documents when delivered asseparately assembly units.

Table 14 Compliance documents

ObjectCompliancedocumenttype 1)

Compliancestandard 2) Additional description

Thruster PC Complete thruster, see definition in Table 1. 3)

Thruster control system PC Complete local- and remotecontrol system forboth steering and propulsion. 3) 4)


1) See DNV-CG-0550 Sec.3 [2].2) Unless otherwise specified the compliance standard is the Society's rules.3) Not applicable for manoeuvering thrusters with power of 300 kW and below. For dynamic positioning thrusters, see

Pt.6 Ch.3 Sec.2 Table 5 and Pt.6 Ch.3 Sec.2 Table 6.4) See Ch.9 Sec.1 [4].



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Table 15 Compliance documents - components

ObjectCompliancedocumenttype 1)

Compliancestandard 2) Additional description

Azimuthing unit: PC When azimuthing unit is delivered as separateunit.

— Housing and structure MC All objects loaded or acting as barrier to sea.

— Propeller nozzle MC

— Assembly bolts > M39 MC

— Assembly bolts ≤ M39 MD

Steering gear unit: PC When steering unit is delivered as a separateunit.

— Housing and structure MC All objects loaded or acting as barrier to sea.

— Assembly bolts > M39 MC

— Assembly bolts ≤ M39 MD

— Torque limiting device PD Applicable for electric steering gear.

— High speed reduction gear PC Normally planetary type, see [4.2.2.6].


MC = material certificate

PD = product declaration

MD = material declaration

1) See DNV-CG-0550 Sec.3 [2].2) Unless otherwise specified the compliance standard is the Society's rules.

1.7.2 General requirementsFor general compliance documentation requirements, see DNV-CG-0550 Sec.4.

1.7.3 Compliance document typeFor a definition of the compliance document types, see DNV-CG-0550 Sec.3.

1.7.4 Reference to other rule chaptersRequirements to sub-components are given in the respective references or in this section:

— shafts, see Ch.4 Sec.1— clutches, see Ch.4 Sec.3— bending compliant couplings, see Ch.4 Sec.4— torsional elastic couplings, see Ch.4 Sec.5— propellers, see Sec.1— hydraulic motor for steering, see Ch.6 Sec.6— pinions and wheels for propeller drive, see Ch.4 Sec.2— pinions and wheels for azimuth steering, see Ch.4 Sec.2.



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1.7.5 Electrical equipment and control systemElectrical equipment and control system shall have compliance documents as required by Ch.8 and Ch.9.

1.8 Workmanship1.8.1 WeldingWelding shall be carried out according to Pt.2 Ch.4.

1.8.2 AncillariesAncillaries, which are not part of the steering gear, but delivered as integral parts of the lubrication, hydraulicoperation and/or cooling systems of the thruster, shall be subjected to a quality control in accordance withthe thruster manufacturer's quality system as found relevant. See also [4.1.2].

Guidance note:Ancillaries: e.g. pumps, electric motors, coolers, piping, filters and valves.


2 Arrangement and operation

2.1 General2.1.1 PerformanceThe installation of a thruster, including alignment, shall be such as to give satisfactory performance under alloperating conditions.

2.1.2 Watertight compartmentAzimuth thrusters shall be mounted in a watertight compartment unless the penetration through the hull issituated above the deepest loaded waterline.

2.1.3 Connection to hullThe thruster shall be mounted so that forces and bending moments can be transferred to the hull without riskof structural failure or harmful vibrations.

2.1.4 Hull connection sealThrusters mounted to the hull by bolted connections, which provide boundary to sea, shall be protected bymeans of a seal.

2.2 Thrusters serving main function propulsion2.2.1 RedundancyThere shall be at least two independent thruster units if the units are serving both propulsion and steering.Functional requirements in Ch.1 Sec.3 [2.3] shall be fulfilled. Combination of propulsion and steering is notdefined as an exception in Ch.1 Sec.3 [2.3.5].Electrically driven thrusters shall fulfil Ch.8 Sec.12.

2.3 Thrusters serving main function steering2.3.1 Vessel steering capabilityFor vessels with more than two steering propulsion units, alternative arrangements to what is required in[2.3.2] may be accepted provided that the vessel's steering capability is maintained after a single failure.Steering capability shall be declared in the operation manual.



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2.3.2 Redundancy requirements for each steering propulsion unitAccording to IACS UI SC242 each steering propulsion unit for SOLAS vessels shall have at least two steeringactuating systems. For non-SOLAS vessels a single steering actuating system per unit may be accepted.A single failure shall neither lead to loss of steering of the vessel, nor consequential damage to the thrusters.Capability requirements in [2.3.4] shall be maintained after a single failure in a steering actuating system.Interconnection between steering actuating systems may be accepted provided ability to isolate eachsteering actuating system after a failure.

2.3.3 Ship type requirementsPassenger ships shall fulfill capability requirements with one steering actuating system out of operation.Cargo vessels shall fulfill capability requirements while operating with all steering actuating system inoperation.

Guidance note:From this it follows that a passenger ships needs at least two steering actuating system with 100% capacity with respect to torqueand speed, while a cargo ship requires minimum two times 50%. This is according to SOLAS requirements, see IACS UI SC 242.SOLAS definitions: A passenger ship is a ship which carries more than twelve passengers, a cargo ship is any ship which is not apassenger ship.


2.3.4 Steering gear capabilityThe steering gear for the thruster shall be capable of:

a) turning the thruster from one side to the other at declared steering angle limits at an average rotationalspeed of not less than 2.3 deg/sec with the ship running at maximum ahead service speed.

b) turning the thruster from one side to the other at declared steering angle limits with one steeringactuating system inactive at an average rotational speed of not less than:

— passenger ships; 2.3 deg/sec with the ship running at maximum ahead service speed— cargo ships; 0.5 deg/sec with the ship running ahead at one half of the maximum ahead servicespeed or 7 knots, whichever is the greater

c) bringing the thruster back to neutral position from any allowable angle at maximum service speed

d) being operated at declared steering angle limits at maximum astern speed without damage.

Topic a), b) and c) shall be demonstrated at sea trial.Guidance note:a), b) and c) are according to SOLAS main steering gear test, see SOLAS II-1 C Reg.29.3.2 and interpretation in IACS UI SC 242.


2.3.5 Power supply

2.3.5.1 Main power supplyEach steering gear shall be served by at least two exclusive circuits fed directly from the main switchboard.However, one of the circuits may be supplied through the emergency switchboard.

Guidance note:This requirement is based on IACS UI SC 242 which is considered equivalent to the SOLAS requirement Reg.30.2.


2.3.5.2 Emergency power supplyThis paragraph applies to steering propulsion units having a certain proven steering capability due to shipspeed also in case propulsion power has failed on this unit.Where the propulsion power exceeds 2500 kW per thruster unit, an alternative power supply shall beprovided automatically within 45 sec. This alternative power supply shall either from the emergency source



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of electrical power or from an independent source of power located in the steering gear compartment. If anindependent source of power is installed, it shall only be used for this purpose.The alternative power supply shall be sufficient at least to supply the steering arrangements and also itsassociated control system and the steering gear response indicator. In every ship of 10,000 gross tonnageand upwards, the alternative power supply shall have a capacity for at least 30 min of continuous operationand in any other ship for at least 10 min.

Guidance note:This requirement is based on IACS UI SC 242 which is considered equivalent to the SOLAS requirement Reg.29.14 for analternative source of power for steering gears, where the required rudder-stock diameter is above 230 mm. The capabilityrequirement is an interpretation of the requirement for an auxiliary steering gear.


2.3.5.3 Short circuit tripSteering gear circuits for electro-hydraulic steering gear shall only trip upon short circuit. If an additionalover-current trip is used, the release current shall be at least 200% of the full load current with a time delayof minimum 60 seconds. In addition, there shall be a phase failure alarm and an overload alarm, see SOLASCh.II-1 Reg.30.3.Steering gear motor circuits controlled through an electronic converter, e.g. for speed control, with currentlimitation set to full load current are exempt from the requirement to only trip upon short circuit.

2.3.6 Thruster compartment

2.3.6.1 AccessThe thruster compartment shall be:

— readily accessible and as far as practicable separated from other machinery spaces— provided with suitable arrangements to ensure working access to thruster and controls.These arrangements shall include handrails and gratings or other non-slip surfaces when required to ensuresuitable working conditions in the event of hydraulic fluid leakage.

2.3.6.2 Ingress protection of electrical power unitsElectrical power units shall have standstill heating and IP-rating as required in Ch.8 Sec.10 Table 1.

2.4 Operation of propulsion thrusters serving main functions2.4.1 Steering gear posterOperating instructions shall be permanently displayed on the bridge and in the thruster compartment. Theoperation instruction shall provide the operator with information on the steering system, consisting of controlsystem and steering gear. Further the operation instruction shall give instruction for the different operationmodes that are available and including how to switch between the operating modes.The instruction shall describe the arrangement and function of the steering gear and control system includinghow to:

— handle failure modes— change–over to/from local control and other operation modes— change-over between control modes on the bridge and in thruster compartment— operate power units in the different operation modes.

Guidance note:Examples of operating modes may be steering gear operation by follow-up mode, non-follow-up mode, local control from thrustercompartment or other pre-defined modes. This is the poster required by SOLAS.




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2.4.2 Crash stopCrash stop shall be possible to execute without inflicting damage to the vessel or its equipment.Non-intuitive procedures shall be described in the operation manual. The ship designer shall ensure that theships stability is not endangered while following the crash stop procedure. Procedures for the crash stop shallbe available on the navigation bridge, see SOLAS Ch.II-1 Pt.C Reg.28.

2.4.3 Modes and conditionsThe following shall be included in the operation manual:

— All operating modes shall be described together with any limitations in performance.— Consequences and handling of failure modes shall be described. This shall include loss of steeringactuating systems and loss of propulsion.

— Operational restrictions in rough sea state shall be described, if applicable. Large vessel motions andaeration of propeller shall be considered.Guidance note:The document will be dependent on information from builder. Operation manual from thruster manufacturer depends on limitationsin performance and strength of the thruster, which is thruster designer's knowledge.


3 Design

3.1 General3.1.1 General capabilityThe thruster shall be capable of withstanding the loads imposed by all allowable operating conditionsincluding effects of thermal expansion and elastic deformations.

3.1.2 Dynamic positioningFor vessels assigned the DYNPOS and DPS class notation, thrusters that are used for dynamic positioningshall be designed for continuous operation, see Pt.6 Ch.3 Sec.1 [6.1] and Pt.6 Ch.3 Sec.2 [6.1].

3.1.3 LoadsThe thruster shall be capable of withstanding loads imposed by worst conditions for which the vessel isdesigned to operate, when operated as described in the operation manual. Due regard shall be paid to loadsoriginating from phenomena such as waves, ship motions and slamming. Grounding loads are not required tobe within the design envelope.

3.1.4 Arrangement for inspection of thruster transmissionIn-dock inspection of thruster reduction gears shall be made possible either through proper inspectionopenings, or by other appropriate means without extensive dismantling.

3.1.5 Safe inspection of podded thrustersPodded thruster internals shall be designed for safe entrance/accessibility to perform necessary maintenanceand inspection without risk neither to personnel nor to damage of equipment.

3.1.6 Piping and ancillary equipmentFor general design requirements for piping and ancillary equipment such as pipes, pumps, filters and coolers,see Ch.6 and Ch.7, as found applicable.Hydraulic components shall be chosen in consideration of the expected level of contamination the system willbe exposed to during its lifetime.Podded thruster flange connections for piping systems shall be located outside the thruster, if practicallypossible.



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Podded thruster flanges and valves inside the thruster shall be arranged to minimise the consequence ofleakage, i.e. by drip trays and leakage drain to safe location.

3.1.7 Alternative designsAlternative thruster designs will be approved based on equivalence, see Pt.1 Ch.1 Sec.1 [2.5.11].

Guidance note:One example may be cycloidal thrusters.


3.2 Housing3.2.1 Stiffness and deflectionsThe thruster structure shall have sufficient stiffness to avoid harmful deflections which may cause damage toother parts of the thruster when exposed to the loads defined in [1.6.3], [3.1.3], [3.1.1].

Guidance note:Examples of topics where deflections in thruster housing structure may have an impact are typically:Internal shafting, rigid connections, sealings, bearing load distribution, pod rotor air gap, contact pattern of gear mesh.


3.2.2 Housing strengthAll housings and structural components (parent material as well as any welds) shall be designed to withstandrelevant fatigue loads as well as extreme loads within the design envelope, see [1.6.3], [3.1.3] and [3.1.1].Such loads shall as a minimum include hydrodynamic loads from propeller or on the housing structure itself.Accelerations shall be considered as found relevant.

3.2.3 General stress requirementsUnless detailed stress calculations are carried out, the following shall be complied with for any design load:

— maximum nominal stress shall not exceed 50% of material yield strength (parent or filler material in caseof welded connection)

— maximum local stress shall not exceed 80% of material yield strength.Guidance note:The above stress limitations are considered to include both static and dynamic (fatigue) strength for simple structures, providedthat a normal thruster load spectrum may be assumed in combination with commonly applied materials (steels and nodular castiron). Otherwise, a more detailed calculation should be carried out, see [3.2.4].


3.2.4 Alternative stress requirementsDetailed stress assessment by means of finite element analysis may be an alternative to [3.2.3].Static stressLoads shall not lead to permanent deflections in the structure when a reasonable safety factor is applied.Dynamic stress and fatigueLoad spectrum shall be substantiated based on relevant experience data (measurements) or conservativelychosen. Sufficient fatigue strength shall be documented applying a reasonable safety factor. A limited numberof discrete load scenarios may be considered individually, or cumulative fatigue strength may be calculatedaccording to Miner's criterion (Miner sum < 1.0). The following shall be included:

— Fatigue strength (SN curve) of material. Such may be derived from recognized standards or widely appliedindustry practices.

— Influence of local stress risers, mean stress, surface roughness, and size effects as applicable.

Safety factor



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A safety factor of 1.5 applied on external loads is considered as a reasonable value. Lower values may beaccepted, depending on calculation methodology and detailed design.

3.2.5 Finite element analysisFinite element calculation may be required for complex housing structures, see also [3.6.3].

3.2.6 WeldingWelded connections forming barrier to the sea shall have full penetration. Welds in zones identified with highstress shall be according to ISO 5817B. Welding shall be according to Pt.2 Ch.4.

3.2.7 Tunnel thrusterThruster tunnels shall be designed in accordance with the requirements in Pt.3 Ch.10 Sec.6 [4].

3.2.8 Propeller nozzleThe propeller nozzle shall be designed in accordance with the requirements in Pt.3 Ch.11 Sec.4 [2].

3.2.9 Retractable thrusterRetractable thrusters shall be designed in compliance with the requirements in Pt.3 Ch.10 Sec.6 [6].

3.3 Propulsion line3.3.1 Shafting

3.3.1.1 DimensionsThe dimensions of the shafts and the shafting components shall be in accordance with Ch.4 Sec.1.For podded thrusters the shafting shall be designed to ensure a sufficient air gap between rotor and statorunder all relevant operating conditions.

3.3.2 Gear transmissions - geared thrusterGear transmissions shall be in accordance with the requirements in Ch.4 Sec.2 as applicable. The number ofload cycles given in Table 16 shall as a minimum be used for dimensioning the gears in the propeller driveline.The safety factors, SF, SH, SHSS, and SS shall at least be as specified in Ch.4 Sec.2 Table 5. The safety factorsfor gears in thrusters for dynamic positioning shall be as for propulsion gears.

Table 16 Thruster type and load cycles

Type of thrusterMinimum number of input shaft revolutions at full power

(NL load cycles)

Propulsion 1) 1·1010

Dynamic positioning 5·108

Manoeuvering 5·107

1) For thrusters subject to frequent overload (intermittent load), relevant load and corresponding accumulated numberof load cycles shall be applied, see also Ch.2 Sec.1 [2].

3.3.3 Propulsion motor - podded thrusterMotor assembly and design shall prevent objects from the rotor to enter the air gap. The poles on the rotorshall be properly secured. The exciter shall be designed for emergency repair or replacement. See also Ch.8Sec.5.



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3.3.4 Rim thruster motorThe rotors and stator shall have means to prevent ingress of sea water to sensitive parts. See also Ch.8Sec.5.

3.3.5 Shaft bearings

3.3.5.1 Fluid film bearingFluid film bearings shall be designed in accordance with the requirements in Ch.4 Sec.2 [2.7.1]. Alignmentcalculation shall be required for large bearings with large variable shaft loads (bending and shear), see Ch.2Sec.4.

3.3.5.2 Ball and roller bearingsBall and roller bearings shall have a minimum basic rated life L10, see ISO 281:2007, as specified inCh.4 Sec.2 [2.7.2]. Calculation is to include the basic rated life (L10) and the modified rated life (L10nm)according to ISO 281.

3.3.5.3 Thrust bearingSeparate thrust bearing shall be designed in accordance with the requirements in Ch.4 Sec.1 [2.9.5]. Heatgenerated within the design limitations (thrust force, shaft speed and lubricant specification) shall not causeexcessive heating.

3.3.5.4 Bearing currentPrecautions shall be taken to prevent harmful stray current in bearings. Insulation and earthing arrangementshall be according to thruster manufacturer's design philosophy.

3.3.6 Shaft sealsA shaft sealing box shall be installed to prevent water from entering internal parts of the thruster or theship. The sealing arrangement shall protect the steel shafts from seawater unless corrosion resistant steel orcoating approved by the Society is used, see Ch.4 Sec.1 [2.12.1], Ch.4 Sec.1 [6.1.2].

3.3.7 PropellerThe propeller and propeller components shall meet the relevant dimensional requirements in Sec.1.

3.3.8 Shaft brake or locking mechanismFor thrusters where wind milling may be detrimental, there shall be a shaft brake or locking mechanismdesigned to hold twice the highest expected wind milling torque when the vessel is operating at safenavigable speed. The mechanism shall be automatically activated within 30 sec after shutdown.Additional lubrication systems may be applied as an alternative to shaft brake unless it is required accordingto Ch.8 Sec.12, see also [3.5.1.5].

Guidance note:Unless otherwise declared for a specific vessel, safe navigable speed means a speed of 7 knots in calm waters and ability tomaintain position in Beaufort 8 with associated sea state conditions. A safe navigable speed for a vessel may alternatively bedeclared through the building specification and hence the contract between the owner and the yard. A safe navigable speed mayalso be declared separately, provided this declaration is approved by the owner.


3.4 Azimuth steering gear for thrusters3.4.1 Manoeuvering and dynamic positioningSteering gear only intended for manoeuvering and dynamic positioning need not comply with [3.4.3.1],[3.4.3.2], [3.4.5.4] and [3.4.10].



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3.4.2 Alternative designsSteering gear other than standard azimuth design with slewing gear and pinions will be approved based onequivalence, see Pt.1 Ch.1 Sec.1 [2.5.11].

Guidance note:Examples are cycloidal thrusters and linked cylinder steering gear.


3.4.3 Steering gear general

3.4.3.1 Sudden turning preventionThe thrusters shall be prevented from sudden turning in the case of power failure, failure in the steeringcontrol system, or any other single failure, except failure in the steering column and/or support bearings.

3.4.3.2 Lock in neutral positionIt shall be possible to bring the thruster to neutral position and lock it to allow it to produce thrust in the casethat one steering actuating system is inoperative. Other azimuth angles than neutral may be accepted whenit is found preferable for the vessel's steering capability.

3.4.4 Azimuthing gear transmission

3.4.4.1 Inspection of azimuth slewing gearInspection of azimuth slewing gear and pinion shall be possible either through proper inspection openings orby other means, e.g. fibre optical instruments, without extensive dismantling.

3.4.4.2 Safety factorsFor reduction gears, the safety factors SF against tooth fracture, SH against pitting, SHSS against subsurfacefatigue and SS against scuffing, shall be minimum as specified in Table 17.

Table 17 Safety factors

SF SH and SHSS 1) SS

2)

Azimuth steering gear

- for surface hardened

- for not surface hardened

1.5

1.5

1.15

1.0

1.4

1.2

1) SHSS is applicable for surface hardened gears only2) SS is not applicable to slow speed gears (pitch line speed < 2 m/s).

3.4.4.3 Self-locking marginAzimuth steering gears shall have a margin against self-locking in order to avoid stick slip effects. The totaldrive train efficiency, excluding the driving motor, shall not be less than 0.65. Self-locking gears may beaccepted on thrusters where single steering actuating system is accepted, see [2.3.2].

Guidance note:Self-locking effect is normally related to worm gears, but the rule requirement applies to all types of gear transmissions.


3.4.5 Electric steering gear

3.4.5.1 Motor controlThe control system for electric motors driving the steering pinion via a mechanical transmission shall bedesigned to avoid abrupt acceleration and shock loads in mechanical parts.



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3.4.5.2 Motor ratingThe electric motors driving the steering gear shall have rating based on specified load spectrum, includingsteering torque, capacity requirement in [2.3.3] and [2.3.4], and for the entire speed range including zero.Alternatively, they shall have a rating S1 according to IEC 60034-1 for the higher torque values.

3.4.5.3 Design steering torqueThe steering gear transmission shall be designed to handle the specified designed steering gear torque,which shall be higher or equal to a torque corresponding the release setpoint for the torque limiting device.

3.4.5.4 Torque limiting deviceIf internal or external transient loads may be detrimental to the mechanical transmission, a torque limitershall be installed in order to prevent load beyond design torque in the steering gear mechanism.The torque limiter shall:

— be the weakest segment in the transmission between motor and azimuth gear— have a static torque capacity of not less than 1.25 maximum working steering torque, maximum workingsteering torque shall be verified at sea trials

— have a sufficient static torque capacity to avoid release during any test carried out at sea trials (to beverified)

— have a sufficient dynamic torque capacity to avoid a sudden turn of thruster during release— be designed without a permanent reduction in torque capacity upon a single release— have a documented durability maintaining at least 90% of rated torque capacity— in case of limited lifetime, be designed so that replacement of device can easily be done at firstopportunity (typically at first time ashore) after release

— have means to identify release and give alarm— be type approved, if standard design (see also DNV-CP-0149). Case by case acceptance may be given, ifsimilar documentation is provided as required for type approval.Guidance note:A mechanical torque limiting device is not necessarily equivalent to a hydraulic safety relief valve as the relief valve has noreduction in functionality and durability after release. From this it follows that durability can either be limited or unlimited.Unlimited durability is to be understood as ability to withstand a number of reliefs corresponding to at least 1 000 accumulated fullthruster rotations, while limited durability corresponds to at least 1 accumulated full thruster rotation.Dynamic torque capacity is ability to transfer torque while in a release condition.


3.4.6 Hydraulic steering gear

3.4.6.1 Hydraulic systemHydraulic systems for steering gears shall not be used for other purposes than operation of thruster unit.Steering circuit piping shall be isolated from circuits to other services when steering is activated.

Guidance note:Steering hydraulic may share the oil sump with systems for propeller pitch control and/or internal lubrication. This is providedthat impurity from one system is not transmitted to the other systems and sufficient cooling capacity is available. Operations likeretracting of thruster is allowed, but loss of oil and oil pressure due to pipe fracture shall not prevent steering.


3.4.6.2 Design pressureDesign pressure shall not be less than the set pressure of the safety relief valve.

3.4.6.3 PipingPiping, joints, valves, flanges and other fittings shall comply with the requirements of Ch.6. Piping intendedfor transmission of hydraulic power shall comply with requirements to class I pipes, see Ch.6 Sec.1 [2.1.5].



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3.4.6.4 Hydraulic system featuresHydraulic power operated steering gear shall be provided with:

a) arrangements to maintain the cleanliness of the hydraulic fluid taking into consideration the type anddesign of the hydraulic system

b) indicator for clogged filter on all filters with a by-pass function.Guidance note:Specification of a pressure filter for maintaining suitable fluid cleanliness may be 16/14/11 according to ISO 4406 and β6-7 (c) =200 according to ISO 16889.


3.4.6.5 Pipe separationSteering actuating systems shall be provided with separate hydraulic power supply pipes.Each hydraulic power unit shall be provided with separate pipes for hydraulic power transmission.Interconnections between power transmission pipes shall be provided with quick operating isolating valves.

3.4.6.6 Relief valvesRelief valves shall be fitted to any part of the hydraulic system which can be isolated and in which pressurecan be generated from the power source or from external forces. Relief valves shall comply with thefollowing:

a) the setting pressure shall not be less than 1.25 times the maximum working pressureb) the setting of the relief valves shall not exceed the chosen design pressurec) the minimum discharge capacity of the relief valves shall not be less than the larger of:

— 110% of the total flow capacity of the pumps— oil flow corresponding to a azimuth unit rotating speed of 5 deg/sec.

Under such conditions the rise in pressure shall not exceed 10% of the setting pressure. In this regard, dueconsideration shall be given to extreme foreseen ambient conditions with respect to oil viscosity.

Guidance note:The hydraulic steering gear is approved against the defined design pressure. The design approval is withdrawn in case requireddesign pressure becomes higher than the chosen design pressure, which may be the case if estimated working pressures are lowerthan the actual measured pressures obtained at trial.The 25% margin is a SOLAS requirement which shall prevent continuous bleeding of relief valves.


3.4.6.7 Hydraulic lockingWhere the steering gear is so arranged that more than one system, either power or control system, can besimultaneously operated, the risk of hydraulic locking caused by a single failure shall be considered.For alarm requirement, see [3.8].

Guidance note:Hydraulic locking includes all situations where two hydraulic systems (usually identical) oppose each other in such a way that itmay lead to loss of steering. It can either be caused by pressure in the two hydraulic systems working against each other or byhydraulic by-pass meaning that the systems puncture each other and cause pressure drop on both sides or make it impossible tobuild up pressure.


3.4.6.8 Flexible HosesFlexible hoses may be used between two points where flexibility is required, but shall not be subjected totorsional deflection (twisting) under normal operating conditions. In general, the hose should be limited tothe length necessary to provide for flexibility and for proper operation of machinery. Hose assemblies shall betype approved. See Ch.6 Sec.9 [4].



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3.4.6.9 Motor ratingThe electric motor driving the hydraulic pump shall at least have a rating S6-25 according to IEC60034-1.Additional class notations or special types of vessels may require other ratings.

3.4.7 Slip ring

3.4.7.1 Electric slip ringThe slip ring unit for transfer of electric main power, auxiliary power, control and monitoring signals shall fulfilrequirements in Ch.8 Sec.8 [1.5].

3.4.7.2 Fluid swivel jointThe fluid swivel joint unit for transfer of any liquid or gas shall be designed against internal and externalleakage. Sealing shall be resistant against wear.

3.4.8 Azimuth seal arrangement

3.4.8.1 Leakage detectionThe slewing seal shall be arranged so that harmful leakage can be detected and drained before water cangain access to water sensitive parts, such as propulsion motor, slewing bearing, and gears.

3.4.9 Slewing bearingThe slewing bearing shall have a design lifetime corresponding to vessel design lifetime or specified overhaulintervals.

Guidance note:ISO 281 is not suitable as the slewing bearing is rotating with a limited rpm and load profile is nearly static. Optional standards toapply are ISO 76, ISO 81400 and IEC 61400. DNV-ST-0377 may be used as a support to the design.


3.4.10 Azimuth brakeThe azimuth brake shall be able to lock the thruster in neutral position, see [3.4.3.2]. The brake holdingtorque shall not exceed design torque if it is a part of the steering actuating system. A locking device fitteddirectly to the slewing gear is accepted as an alternative to a brake. This locking device may be withouttorque limitation. Manual release of the brake or locking mechanism shall be possible.

3.5 Auxiliary systems3.5.1 Lubrication

3.5.1.1 Arrangement and capabilityThe lubrication system shall be designed to provide all bearings, gear meshes and other parts requiring oilwith adequate amount of oil for both lubrication and cooling purposes. This shall be maintained under allenvironmental conditions as stated in Ch.1 Sec.3 [2.2].Lubricating oil systems shall comply with Ch.6 Sec.5 [3] as applicable.

3.5.1.2 Pod bearingsAll shaft bearings in podded thrusters shall have lubrication oil system providing cleanliness, temperature,and lubrication. Each bearing assembly shall have separate lubrication oil distribution.

Guidance note:Alternative solutions may be accepted provided appropriate cleanliness, temperature, and lubrication for all shaft bearings.


3.5.1.3 Lubrication systemThe lubrication system shall include:



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— an arrangement to take representative oil samples with respect to detecting water and particlecontamination

— if necessary, a cooler to keep the oil temperature within the specified maximum temperature, whenoperating under the worst relevant environmental conditions, see [3.5.1.1]

— a filter of suitable fineness for gearing, hydraulics and bearings, see [3.3.5.2].Guidance note:Specification of a pressure filter for maintaining suitable fluid cleanliness may be 16/14/11 according to ISO 4406 and β6-7 = 200according to ISO 16889.


3.5.1.4 Filter arrangementFor propulsion and dynamic positioning thrusters it shall be possible to change or clean filters withoutinterrupting the bearing operation. Filter design requirements as for hydraulic systems [3.4.6.4].

3.5.1.5 Wind millingForced lubrication may be used as an alternative to shaft brake [3.3.8] unless required in Ch.8 Sec.12. Apump for this purpose shall be additional to any standby pump required by other parts of the rules. Thepump shall be automatically activated within 30 sec after shutdown of the thruster.

3.5.1.6 Low rpm operationFor thrusters designed to operate at such low rotational shaft speeds that an attached pump (if needed)cannot supply sufficient amounts of oil, the following may be accepted:

— either an extra electric oil pump that is activated at a given pressure in addition to the attached pump, or— 2 electric main pumps of the same capacity, one of which is arranged as a standby pump with immediateaction. These pumps shall be supplied from different sides of the main power distribution.

3.5.2 Cooling

3.5.2.1 Sea water systemsWater cooling systems shall comply with Ch.6 Sec.5 [2], as applicable.

3.5.2.2 Heat balanceThe cooling system, if applicable, shall have heat transfer capacity enough to keep the propulsion machinerywithin the design temperature range at the maximum propulsion power and the environmental conditions asspecified in Ch.1 Sec.3 [2.2]. Some reduction in propulsion power may be accepted when operating in hotenvironments based on the heat balance analysis and the specification of power reduction.

3.5.3 Bilge systemPodded thrusters shall be provided with a drainage system, which shall be activated automatically.

3.6 Vibration3.6.1 Torsional vibration, propulsion line

3.6.1.1 Torsional vibration analysisFor details regarding torsional vibration calculation and analysis, see Ch.2 Sec.2.

3.6.1.2 RIM thrusterTorsional vibration calculation is not required for RIM thrusters independent of application.



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3.6.1.3 Electric and hydraulic driven tunnel thrustersNatural frequencies are not permitted in the range of 0.8-1.2 times the blade order frequency at ratedpropulsion power for the thruster unless the vibratory torque is documented to be within approved limits (KAfactor).

Guidance note:The relation between power and speed in the propeller law is P~n3, which implies that excitation harmonics are highest atmaximum speed. Application factor KA is defined in Ch.4 Sec.2.


3.6.1.4 All other thrustersForced torsional vibration calculated shall be made for normal operation as well as for extreme steeringmanoeuvres. The excitation used for extreme steering manoeuvres shall be substantiated.Forced calculation is not required for podded thrusters with lowest natural frequency higher than 2nd bladeorder excitation frequency, see Ch.2 Sec.2 [1.4.1].For propulsion plants the application factor KA shall be minimum 1.10 for normal operation, for calculationpurposes.

Guidance note:Fatigue assessment in the torque transmission line is based on dynamic response, described by the application factor, KA. KA isrelated to high cycle fatigue.KAP describes non-frequent peak loads, and is related to (very) low cycle fatigue/static strength. During extreme steering (e.g.steering gear test) dynamic response in the range between KA and KAP is expected, mainly due to oblique inflow to the propeller.Level of the application factor during such manoeuvres as well as number of associated load cycles will depend on ship type andapplication.Values for propeller excitation as given in Ch.2 Sec.2 [2.3.3] are expected to result in application factors to the conservative side.Lower values for propeller excitation may be accepted when substantiated by relevant measurements and/or advanced numericalcalculations.


3.6.2 Torsional vibration, steering gear

3.6.2.1 ResonanceSteering gear mechanical drive train shall be designed to avoid harmful vibrations originating fromresonances due to external loads (e.g. vortex shedding or dynamic blade loads).

3.6.2.2 TransientsTransient external loads within expected operations shall not exceed the release load of the torque limitingdevice or safety relief valve.

3.6.3 Housing vibration modesConsequences from resonant vibrations in housing, including impact on other structures, systems orcomponents shall be considered. Calculation of natural frequencies and modes by finite elements analysismay be required, see also [3.2.4].

Guidance note:Excitation sources are typical hydrodynamic loads at blade passing frequencies and vortex shedding during steering in combinationwith vessel speed.




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3.7 Special design features3.7.1 Retractable thrustersThe thruster shall have means to prevent lowering to operational position when vessel speed is above designlimit. The thruster shall have a locking functionality in operating position before engagement of the propeller.Hydraulic hoses and pipes shall be protected against damage from objects or contact with structure.

3.7.2 Flexibly mounted tunnel thrusterThe arrangement of flexibly mounted tunnel thrusters shall provide effective protection against flooding.Such thrusters shall be placed in a separate watertight compartment, unless the flexible sealing arrangementcontains two separate effective sealing elements. An arrangement for indication of leakage into the spacebetween the inner and outer sealing shall be provided. The arrangement shall allow inspection of suchsealings during bottom survey without extensive dismantling. One watertight compartment may containmore than one thruster but shall not share compartment with propulsion thrusters.

3.8 Control and monitoring systems3.8.1 General - propulsion thruster arrangementThe requirements of this subsection are additional to the requirements for design and arrangement of electricsystems Ch.8 and control systems Ch.9.

Guidance note:Additional requirements for thruster control and monitoring apply to vessels with certain class notations, e.g. DYNPOS, RP(n,%),SRTP.


3.8.1.1 Functional requirementsThe control, monitoring, and safety systems shall be arranged to ensure safe and reliable operation of thethruster installation.

3.8.1.2 Control positionsPropulsion thruster arrangements shall be provided with necessary means for remote control from bridge andlocal control from appropriate location(s) in the thruster and drive compartment(s), covering both steering-and propulsion control.

3.8.1.3 System arrangementThe propulsion thruster control systems shall be arranged with:

— independent controllers dedicated for each thruster— means of local control including necessary monitoring and indicators independent for each thruster, seeTable 19.

3.8.1.4 Local controlThe local control shall provide the following capabilities:

— include necessary means for both command and monitoring of the necessary parameters to enable a safeoperation of the propulsion- and steering system

— be independent of the remote control— it shall be possible from the local command position(s) to disable remote control— azimuth angle indicator and heading information shall be available at the local steering position(s)— heading information shall be automatically updated when power is restored after a power failure— efficient means of two-way voice communication between the local control position(s) and the bridge andengine control room.



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Guidance note:The local command positions may be locally at the electrical drives/frequency converters for the propulsion and steering units.


3.8.1.5 Remote control

a) The remote control system for propulsion and steering may be arranged in a common system, providedthat the specific requirements for the steering and propulsion functions, see [3.8.3] and [3.8.2]respectively, are complied with.

Guidance note:The requirements for the remote control systems for steering and propulsion differ; the strictest requirements apply to thesteering function. The remote control functions may be implemented in a common system or in separate systems, in eithercase, the requirements specific for each functions apply.


b) For propulsion thruster arrangements, the main command location for remote control is the bridge. Thisimplies that if other locations are equipped with means for remote control of propulsion and steering, itshall be possible to take command of the propulsion thrusters from bridge.

c) For any additional locations equipped with means for remote control of propulsion thrusters, the generalprinciples of command transfer as given in Ch.9 shall be complied with.

Guidance note:Additional remote control positions may e.g. be engine control room (ECR) or an safe return to port (SRTP) bridge forpassenger ships.


3.8.1.6 Emergency stopEmergency stop of each individual propeller shall be possible from bridge, arranged independently of theremote control system.If the independent stop facility is arranged as an emergency stop push button, this shall be arranged inaccordance with Ch.8 Sec.2 [8.6.1].

3.8.1.7 Alarm and monitoring

a) Any alarm condition in the thruster plant shall initiate an alarm at the navigating bridge and/or ECRaccording to the principles in this subsection. For unattended machinery operation, the ECR alarms shallbe given through the extension alarm system.

b) For propulsion thruster arrangements, the extent of alarms presented at the navigating bridge shall belimited to those that require attention from bridge personnel, according the following categories:

— alarms that require immediate attention and actions from the bridge personnel, to maintain or restorefunctionality of thruster systems; to maintain the safe navigation and operation of the ship

— warnings of failures and conditions that may indicate reduced capabilities, performance or faulttolerance in the thruster systems without the need for any immediate actions from bridge personnel.Warnings are presented for precautionary reasons to bring awareness of changed conditions whichare not immediately hazardous, but may become so, if no action is taken.

c) Warning may be presented individually or in groups provided:

— only warnings of the same category that represent conditions of similar consequence may bepresented in the same group

— each individual alarm triggering the group alarm shall be identifiable in ECR or at the local controller /control panel from where the alarm originated

— that the functionality of group alarms are according to Ch.9 Sec.3 [1.5].

d) All alarms shall be presented in ECR, also those presented at the navigating bridge. Acknowledgmentshall in general be possible from one location only. Only alarms that specifically demand attention from



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the navigation bridge shall be acknowledged from the bridge, e.g. deviation alarm, failure of remotecontrol, all other alarms shall be acknowledged in ECR.

e) Remote alarm and monitoring functions for all thrusters may be arranged in a common system.

f) The alarming and monitoring of the thruster installation shall in general cover:

— the contents of Table 18— if electrically driven, in accordance with Ch.8 Sec.12 [1.6].

g) RPM and pitch of each individual propeller shall be indicated at all control position.

3.8.2 Steering

3.8.2.1 System arrangement

a) The remote steering control system shall be arranged with two independent means of steering from thenavigating bridge, e.g. arranged as:

— independent control systems for the steering of each thruster, or— if a common, integrated system is arranged for the control of all thrusters, an independent back-upmeans of remote control shall be provided for each thruster, with similar input devices/levers as thenormal control.Guidance note:An integrated system arranged with redundancy is in general not considered to provide equivalent fault tolerance asindependent systems, hence a redundant system will not be accepted to meet the above requirement without additionalindependent means of control.


b) The independent steering control systems shall be arranged with:

— physical segregation and not be located in the same enclosure (cabinet, desk, panel), unless a flame-retardant partition is installed between the control systems within the enclosure

— cables and pipes segregated as far as practicable throughout their length.

c) A common main steering stand without segregation serving both steering control systems is acceptable,provided that cables and components are securely installed to limit the potential for physical damageimpairing both systems.

d) Steering order devices for the independent control systems may be operated by the same lever shaft.

e) The devices for mode selection and transfer of command between control positions may be implementedin common units provided that no single failures may propagate to the independent steering controlsystems. The mode selection shall be displayed at all control positions.

3.8.2.2 Response to failuresA failure in the steering control system shall lead to the least critical state of the thruster. If a failure lead toloss of control, the thruster shall normally freeze in its present position.

Guidance note:The least critical condition is normally to freeze the thruster in its present position. For systems and/or operational modes wheremidship position is considered to be the least critical condition, this may also be accepted.


3.8.2.3 Steering gear power units

a) The steering gear power units shall:

— normally be part of the remote start-up sequence for the thruster. If the thruster unit is designedfor operational modes where manual start and stop of steering power units is required, remote start



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and stop of the individual power units shall be arranged from the bridge and possible other positionswhere remote control of thrusters is available

— designed for parallel operation of all steering gear power units in normal operation— designed to automatically or manually stop failed units, maintaining the required steering capabilitieswith the remaining power units

— provided with an overload alarm activated when the current exceeds full working load.

b) The protective shutdown functions associated with the steering gear shall be limited to those necessaryto prevent immediate machinery breakdown. Any protective shutdown shall initiate an alarm.

3.8.2.4 Alarm and monitoring

a) The presentation of alarms on the bridge shall be readily observable from the main steering stand. Theuser interface for alarm presentation shall provide a continuous and an efficient display of the status ofalarms and warnings.

Guidance note:

This may be provided by dedicated displays/screens or by user interfaces with dedicated areas for a continuous statusoverview where details of alarm conditions may be activated by simple manual actions.


b) A deviation alarm shall be initiated if the thruster's actual position does not reach the set point withinacceptable time limits for the closed loop control systems, e.g. follow-up control and autopilot.

3.8.2.5 Azimuth angle indicationThe azimuth angle of each propulsion thruster shall be indicated at the bridge by at least two differentsystems, one of them independent of any other control system. The system shall for each of the thrusters bearranged so that a single failure in power supply, or anywhere in the indicating system, does not cause lossof azimuth angle indication on the bridge.

3.8.2.6 Power supplyThe power supply to the each of the steering control systems shall be either:

— fed by a separate circuit supplied from the steering gear power circuit from a point within the steeringgear compartment, or

— fed directly from the switchboard busbars supplying that steering gear power circuit at a point on theswitchboard adjacent to the supply to the steering gear power circuit.Guidance note:The intention is to ensure that the power unit and the control systems as far as practicable maintain its power supplysimultaneously, i.e. that whenever the power unit is powered, the control system is powered.


3.8.3 Propulsion

3.8.3.1 System arrangementFor propulsion control a common remote-control system may be arranged if the system is redundant/singlefail tolerant.

3.8.4 Power supply

a) The power supply to the thruster control system shall be arranged according to Ch.9 Sec.3 [2.2.3], Ch.9Sec.3 [2.2.4] and Ch.9 Sec.3 [2.2.5].

b) The power supply to the thruster control system shall, in addition, be fed from uninterrupted powersupplies (UPS).

c) The power supply to the navigation equipment (i.a. RPM, pitch) shall be powered from the emergencyswitchboard, see SOLAS Ch.II-1 Reg.42, 43 and Ch.V Reg.19.



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3.8.5 General - manoeuvring thruster arrangements

a) Manoeuvring thrusters shall be provided with individual emergency stop of propellers from the bridge.The emergency stop function shall be independent of the remote control system, if fitted.

b) Manoeuvring thrusters shall be provided with alarm and monitoring according to Table 18.

3.8.6 Alarms and indication

Table 18 Alarm and indication list

System/Item

Gr 1Indicationand/or alarm

Gr 2Automaticstart ofstand-by pumpwith alarm

Gr 3Shut downwith alarm

Comment

1.0 Electrical prime mover1)

Load (torque)2)IR6),HA 3),6)

2.0 Pitch speed and direction of rotation

Propeller speed IR6) For constant speed propellers, runningindication is acceptable.

Direction of rotation for reversiblepropellers IR6)

Propeller pitch for CP-propellers IL, IR6)

For main propulsion, the following pitchsettings shall be marked on the localpitch indicator: mechanical pitch limitsahead and astern, pitch at full aheadrunning, maximum astern pitch andpitch at zero thrust. For manoeuveringand dynpos thrusters; maximum,minimum and zero pitch are sufficient.

3.0 Hydraulic system for CP-propeller

Pressure IL, LA AS4)

Level IL, LA2) If separate tank.

Differential pressure over filter HA Applicable for propulsion thrusters.

4.0 Bilge system

Level HA For podded thrusters.

5.0 Lubricating oil

Pressure IL2) , LA AS5) If forced lubrication oil system.

Temperature IL, HA2)

Level IL, LA

6.0 Steering system

Azimuth angle IL, IR6)



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System/Item




Comment

Hydraulic oil pressure IL, LA

Hydraulic oil supply tank level IL, LA

Hydraulic oil temperature HA, IL

Azimuth brake engaged IR6)

Electric power failure A6) Steering gear power unit.

Electric motor overload A6) Steering gear power unit.

Torque limiter release A6), IL For mechanical torque limiterarrangements.

7.0 steering gear control system

Power failure of control system A6)

Remote control disconnected A6), IR6)

Control failure A6)

Earth fault on AC and DC circuits A6)

Loop failures in closed loop system(command and feedback) A6) Normally short circuit, broken

connections and earth faults.

Deviation between steering orderand feedback A6) See b) in [3.8.2.4].

Overload alarm and phase failurealarm A6) See [2.3.5.3].

8.0 Cooling medium

Temperature HA, IL For podded thrusters.

9.0 Special features

Thruster ready for use IR6) For retractable thrusters.

Seal leakage IL, LA For flexibly mounted tunnel thrusters.



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System/Item




Comment

Gr 1 = sensor(s) for indication, alarm, load reduction (common sensor permitted but with different set points andalarm shall be activated before any load reduction)

Gr 2 = sensor for automatic start of standby pump

Gr 3 = sensor for shutdown

IL = local indication (presentation of values), i.e. in vicinity of the monitored component

IR = remote indication (presentation of values), in engine control room or another centralized control station suchas the local platform/manoeuvering console

A = alarm activated for logical value

LA = alarm for low value

HA = alarm for high value

AS = automatic start of standby pump with corresponding alarm

LR = load reduction, either manual or automatic, with corresponding alarm, either slow down (rpm reduction) oralternative means of load reduction (e.g. pitch reduction), whichever is relevant

SH = shut down with corresponding alarm. May be manually (request for shut down) or automatically executed, ifnot explicitly stated above.

All alarms shall be routed to the engine control room (ECR), see a) in [3.8.1.6].

For definitions of load reduction (LR), and shut down (SH), see Ch.1.

1) regarding electric motors, see Ch.8 Sec.12 [1.6.4]2) not required for manoeuvering thrusters, except if part of a dynamic positioning system3) set point to be set according to rating4) to be provided when stand-by pump is required, see Sec.1 [6.3]5) to be provided when stand-by pump is required, see [3.5.1]6) indication/alarm to be presented at navigation bridge in addition to ECR.


4.1 General4.1.1 ScopeThe parts in a thruster shall be tested and documented as described in Table 14, Table 15, Table 19 and Table20.Visual inspection shall be carried out of all parts mentioned in Table 14 and [1.7.4].Tests and inspections shall be carried out by the manufacturer, and the Society shall be invited for inspection.



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ObjectUltra-sonic (UT) or

X-ray (RT) testingSurface crackdetection Pressure testing Visual inspection (VT)

Housing,

welded barrier to sea

and critical welds

20% 20% Tightness 100%

Housing,

other weldingfull penetration

5% 5%

Housing,

other welding5%

Housing,

castingSee Pt.2 Ch.2Sec.8 [2.5]

See Pt.2 Ch.2Sec.8 [2.5]

Assembly bolts > M39 Applicable Applicable Applicable

Assembly bolts ≤ M39

4.1.2 AncillariesAncillaries integrated as part of the thruster and not covered by Table 14, Table 15, Table 19 and Table 20,shall be tested and inspected as found relevant by the thruster manufacturer.

4.1.3 Prototype testingFor novel technology or designs unknown to DNV a prototype testing or other arrangements for qualificationof technology may be required. Scope shall be agreed with the Society in advance.

Guidance note:The prototype test is required to build confidence to the component, system or arrangement which contains novel technology ornew unknown design. For smaller units or assemblies, it is preferable to carry out the test in workshop. For large assemblies orunits the tests may be executed after installation on board if accepted by all parties. In such cases will the product certificate beissued after the test. The test may be limited to parts of the thruster or full-scale test of a complete thruster.


4.2 Workshop testing4.2.1 General

4.2.1.1 Electrical equipmentTesting of electrical equipment, such as motors and frequency converters, shall comply with Ch.8.

4.2.1.2 Instrumentation and controlTesting of instrumentation and control systems shall comply with Ch.9.

4.2.1.3 Propeller fittingFor propeller fitting, see Ch.4 Sec.1.

4.2.1.4 Leak testThe azimuthing unit shall be subjected to leak testing (internal pressure, soap water test or similar).



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4.2.2 Steering gear

4.2.2.1 Steering gear parts - extent of testingSteering gear parts shall be inspected and tested as required by Table 20. The visual inspection shall includeverification of compliance with approved drawings. Attention shall be paid to critical dimensions, clearancesand stress raisers.

4.2.2.2 Hydraulic pumps - type testingEach type of hydraulic pump shall be subjected to a type test.

a) The type test shall be for duration of not less than 100 hours.b) The test arrangements shall be such that the pump may run in idling conditions, and at maximum

delivery capacity at maximum working pressure.c) During the test, idling periods shall be alternated with periods at maximum delivery capacity at

maximum working pressure.d) The passage from one condition to another should occur at least as quickly as on board.e) During the whole test no abnormal heating, excessive vibration or other irregularities are permitted.f) After the test, the pump shall be dismantled and inspected.Type tests may be waived for pumps which has been proven to be reliable in marine service.

4.2.2.3 Hydraulic piping - pressure testingThe rule requirements related to the testing of class I pressure vessels, piping and related fittings apply.The steering gear is subject to internal pressure testing for a test pressure, Ptest, 1.5 times the designpressure, but need not exceed the design pressure by more than 70 bar.Holding time shall be sufficient for detection of leakages, however not less than 15 minutes, see Ch.6 Sec.5[8.5.1] and Ch.6 Sec.10 [5.1].

4.2.2.4 Hydraulic safety relief valveThe safety relief valves shall be tested and verified.

4.2.2.5 Mechanical torque limiterThe mechanical torque limiter shall be adjusted and marked with the release torque. Individual testingand adjustment may be omitted if it is a mass-produced off-the-shelf product with torque pre-set from thesupplier.

4.2.2.6 High speed gear boxFor propulsion thrusters which have steering actuating systems consisting of high speed hydraulic or electricmotors which are combined with off-the-shelf, mass-produced gear boxes, the certification of the gearboxesmay be based on function testing only, provided that:

— the vessel is fully manoeuvrable with one thruster locked in worst possible condition, while the remainingthrusters are fully operable.

— each thruster is provided with two or more steering actuating systems— the gearboxes shall be conservatively chosen with regard to required safety factors and able to handle allrelevant loads for the steering gear

— the gearboxes are easily replaceable.Guidance note:Conservatively chosen is typically to go one size up in catalogue data compared to the smallest gear satisfying the safety factorsin an ordinary design approval,, or an additional 5% margin to the required safety factors (i.e.: multiply the required safety factorwith 1,05). This will simplify the certification process, especially for planetary gear transmissions.


4.2.2.7 Steering gear - test after assemblyThe assembled steering gear is subject to function test.



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4.2.3 Azimuth unit assembly

4.2.3.1 Hydraulic system - pressure testingSystems for lubrication and hydraulic pitch control shall be function and pressure tested. The test pressureshall be as required in [4.2.2.3]. Regarding function testing of controllable pitch propellers, see Sec.1 [3.1].

4.2.3.2 Propulsion gearAssembly of the drive gears regarding tooth contact shall be in accordance with the approved design. Forgear mesh check, see Ch.4 Sec.2 [4.1]. Alternative gear mesh check procedures may be approved on a case-by-case basis.

4.2.3.3 Drainage systemDrainage system for podded thrusters shall be function tested.

4.2.4 Other systems and components

4.2.4.1 Function test retractable mechanismsThe mechanism for lowering and lifting the thruster, including safety functions, shall be function tested.

4.2.4.2 Pressure test, retractable mechanismsHydraulic systems for retractable mechanisms shall be function and pressure tested. Test pressure shall be asrequired in [4.2.2.3].

4.3 Installation on board4.3.1 MountingThe mounting and installation of the thrusters shall be in accordance to approved drawings and according tomanufacturer's specification.

4.3.2 Integration planIntegration tests covering propulsion and steering systems, including subsequent networks, shall beaccording to the integration plan.

4.3.3 Assemblies carried out remoteSub-assemblies and parts mounted at yards or workshops other than the thruster manufacturers' shall becarried out according to the thruster manufacturer's instructions.

4.3.4 Electric propulsionSee Ch.8 Sec.12 [2.1.1].

4.3.5 Gear inspectionFor accessible thruster reduction gears, the requirements in Ch.4 Sec.2 [8] apply.

4.3.6 ShaftingFor shaft alignment, propeller fitting and assembly of shafting components, the requirements in Ch.4 Sec.1[7] apply.

4.3.7 Steering gear testAfter installation on board the vessel, and prior to sea-trial, the steering gear shall be subject to the requiredhydrostatic and running tests.The test shall as a minimum include:



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a) hydrostatic testing:

— parts of steering gear that has not been pressure tested at workshop shall be tested as in workshop,see [4.2.2.3]

— assembly shall be tested at design pressure

b) function testing of the steering gear

c) testing alarms and indicators

d) automatic start test of power units

e) testing of all start and stop functions

f) testing of control transfer between bridge and local control

g) testing of safety valve setting (if not performed during workshop test)

h) testing of function and setting of overcurrent protection

i) test and check of functions and settings in frequency converter (if applicable)

j) checking mechanical steering angle indicator.

4.4 Sea trial4.4.1 Electric propulsionSee Ch.8 Sec.12 [2.1.2].

4.4.2 Standards for ship manoeuvrabilityManoeuvring tests as described in IMO Res. MSC137(76) shall be carried out, also for non-SOLAS ships.

4.4.3 Steering capability and turning speedFor azimuth propulsion thrusters, the steering capability shall be tested, and azimuthing turning speed shallbe verified to be in compliance with [2.3]. Declared steering angle limits are not to be exceeded during thetests.

4.4.4 Test conditionSteering and reversing functions shall be tested under the most severe permissible conditions, at least withfull ahead vessel speed and at full draught.

Guidance note:In this context condition is related to ship condition and modes and not environmental conditions which is described in IMO Res.MSC.137(76).5.2.


4.4.5 Operating modesAll operating modes for the vessel, as defined in the operating philosophy, shall be tested.

4.4.6 Steering torque measurementSteering torque, derived from electric current or hydraulic pressure, shall be measured and recordedcontinuously during the steering gear test, see [4.4.12]. Steering torque in auto pilot mode shall berecorded. Recordings shall be compared with acceptance criteria for speed and capability in [2.3.3] and[2.3.4] and for torque or pressure in [3.4.6.2], [3.4.6.6] or [3.4.6.2], [3.4.6.6].

Guidance note:Dedicated instrumentation for this test is not required if data can be derived from the thruster's control and monitoring system.




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4.4.7 Crash stopCrash stop test from full available speed ahead shall be performed according to a defined procedure.

Guidance note:Vessels with traditional shafting will perform the crash stop by reversing propeller thrust by use of shaft speed and propeller pitch.Vessels having thrusters for main propulsion may reduce the stop length by use of steering gear according to procedures oftenrecommended by manufacturer. The test is reflected in IACS UI SC242 reg.28.3.


4.4.8 Control, alarm and safety functionsThe control, alarm and safety functions shall be tested for compliance with the approved alarm list, see Table18.

4.4.9 Podded thrustersPodded thrusters shall be inspected internally after sea trial and full load test for leakage or any otherabnormalities.

4.4.10 Retractable thrustersRetractable mechanism including locking functionality shall be function tested in combination with propellerengagement.

4.4.11 Thruster gearsAll accessible thruster gears shall be inspected as in Ch.4 Sec.2 [9].

4.4.12 Steering gear testThe steering gear shall be tested during sea trial in order to demonstrate the function of the steering gearand that the rule requirements have been met.The test shall include the following:

a) Testing of steering gear function and capacity. Acceptance criteria are given in [3.4.3].b) The steering gear power units, including transfer between steering gear power units.c) The isolation of one steering actuating system, checking the time for regaining steering capability.d) The emergency power supply required in [2.3.5.2].e) The steering gear controls, including transfer of control and local control.f) The means of communication between the steering thruster compartment and the bridge. Also, with

the engine room/engine control room, if applicable. The test may be carried out and completed at thedockside.

4.4.13 Test recordA record of the steering gear, and propulsion parameters during test, shall be presented to the Society. Seealso documentation requirements in Table 5.

5 Required compliance documentation in other rules chaptersThrusters are assembled units which consist of several components and subsystems with individualrequirements to certification based on design approval and tests. These requirements are found in variousrule chapters and sections in Pt.4 as applicable.Table 20 is presented as a support to the reader with references to requirements which may be applicable.

Table 20 Certificates required in other rule chapters

Item Rule reference

Propeller cast in one block Sec.1



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Item Rule reference

Separate blades Sec.1

Separate hubs Sec.1

Hub caps with fins Sec.1

Blade bolts Sec.1

Controllable pitch mechanism Sec.1

Pitch control and monitoring system Sec.1

Shafts in thrusters and gears Ch.4 Sec.1

Other shafts for propulsion Ch.4 Sec.1

Other rigid couplings/couplings inthruster Ch.4 Sec.1

Keys bolts shear pins Ch.4 Sec.1

Propeller shaft liners Ch.4 Sec.1

Shaft sealing rings Ch.4 Sec.1

Propeller shaft sealing Ch.4 Sec.1

Gear transmission Ch.4 Sec.2

Pinion and wheel Ch.4 Sec.2, if sub-contracted

Pinion and wheel Ch.4 Sec.2

Built in clutches Ch.4 Sec.2

Shaft rigid couplings hubs Ch.4 Sec.2

Welded gear and couplings Ch.4 Sec.2

Bolts and keys Ch.4 Sec.2

Clutches Ch.4 Sec.3

Bending couplings Ch.4 Sec.4 bending comp. Couplings, if main function and ≥ 5000 kW or 5 kNm

Bending couplings Ch.4 Sec.4 bending comp. Couplings, std design

Torsional elastic couplings Ch.4 Sec.5 Torsional elastic couplings, if main function and ≥ 5000 kW or 5 kNm

Torsional elastic couplings Ch.4 Sec.4 bending comp. Couplings, std design

Hydraulic pumps Ch.6 Sec.1

Other valves Ch.6 Sec.1

Hydraulic cylinders Ch.7, pD > 20 000

Flexible hoses with couplings Ch.7

Accumulators Ch.7, pV > 1.5

Electric sliprings Ch.8 Sec.1

Electric motors Ch.8 Sec.1, ≥ 300kW



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Item Rule reference

Electric motors Ch.8 Sec.1, ≥ 100 kW and < 300kW

Cables Ch.8 Sec.1

Termination accessories (aluminiumcables) Ch.8 Sec.1

Control and monitoring system -remote and/ or automatic control ofpower system

Ch.8 Sec.1

PC = Product certificate

MC = Material certificate

PD = Product declaration

MD = Material declaration

TAC = Type Approval Certificate

PTR = Product test report

MTR = Material test report

1) See DNV-CG-0550 Sec.3 [2].



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SECTION 4 COMPRESSORS

1 General

1.1 Application

1.1.1 These rules apply for compressors as a part of the following systems:

— those with design pressure above 40 bars— starting air, see also Ch.6 Sec.5 [9.4]— instrument / control air, see also Ch.6 Sec.5 [9.2.2]— breathing gas for diving systems, see also DNV-OS-E402— recharging breathing air cylinders for fire fighters, see also Pt.5 Ch.10 Sec.9— cargo refrigeration (for ships having additional class notation RM), see also Pt.6 Ch.4 Sec.9— cargo, fuel, refrigeration and nitrogen plants (for ships having class notation Tanker for liquefied gas),see also Pt.5 Ch.7

— nitrogen generators (for ships having class notation Tanker for chemicals), see also Pt.5 Ch.6 Sec.1— for regasification plants (vessels with class notation REGAS), see also Pt.6 Ch.4 Sec.7— for gas fuelled ship installations (vessels with class notation Gas fuelled), see also Pt.6 Ch.2 Sec.5— for gas power plants (vessels with class notation Gas power plants), see also Pt.6 Ch.5 Sec.20— inert gas production (when such a system is required by SOLAS and for ships having additional classnotations Inert), see also Pt.6 Ch.5 Sec.8.

1.1.2 Compressors for hydro carbons are subject to special consideration.Compressors for hydro carbons intended for offshore installation and following offshore regime (offshorestandards and codes) shall comply with a recognised national or international standard.Compressors for hydro carbons intended for ship system and subjected to classification shall comply with arecognised standard. Required documentation shall be agreed upon with the Society.

1.1.3 Design approval is required for all compressors as listed in [1.1.1] and with a shaft power exceeding200 kW.

Guidance note:Shaft power is seen as a power of motor driving compressor


1.1.4 Product certificate is required for all compressors as listed in [1.1.1] and as specified in [1.4.3].

1.1.5 The rules in this section apply for the compressor only. Any additional equipment, e.g. prime movers,pressure vessels, piping, electric equipment and instrumentation shall comply with relevant parts of the DNVRules.

1.2 DefinitionsTable 1 Definitions

Term Definition

Compressor mechanical device that increase the pressure of gas by reducing its volume. The increase ofpressure may be carried out by pistons, screws, diaphragms or centrifugal compressors.



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Term Definition

Reciprocating compressor positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases athigh pressure.

Screw compressor type of rotary compressor which compresses air due to screw action.

Centrifugal compressorstype of dynamic compressor with a radial design. Dynamic compressors work at a constantpressure and the performance is affected by external conditions such as changes in inlettemperatures.

Turbo compressors centrifugal compressor where the air is drawn in axially, accelerated to high velocity and thenexpelled in a radial direction.

Boosters (Maximizers) A compressor designed with inlet (suction) pressure above atmospheric is to be entitled as abooster (maximizer).

Hydro carbons organic compound consisting entirely of hydrogen and carbon

A system (in the contextof this section)

A system normally contains additional auxiliary components like pressure vessels, additionalpiping, overflow, gas coolers, water taps, pulsation snubbers etc. and may be mounted onthe skid.

1.3 Documentation1.3.1 Design approvalDocumentation according to Table 2 shall be submitted for compressors when design approval is required[1.1.3]. Additionally, depending on compressor type the documentation as mentioned in Table 3 or Table 4shall be submitted.

1.3.2 Compressors of special type and designFor compressors of unconventional type and design, the extent of the documentation shall be considered ineach case.

1.3.3 Requirements and definition for documentationFor general requirements for documentation, including definition of the info codes, see DNV-CG-0550 Sec.6.

For a full definition of the documentation types, se DNV-CG-0550 Sec.5.

Table 2 Documentation requirements for all compressors


C020 - Assembly orarrangement drawing Cross section FI

I110 - List of controlled andmonitored points

Alarm set points and delaytimes. AP

S010 Piping diagram Compressed medium,lubrication and cooling APCompressor

Z110 - Data sheet

Medium, design pressurefor all stages, workingtemperature, capacity,maximum shaft power andmaximum rotational speed.

FI



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Table 3 Additional documentation for reciprocating compressors and boosters (maximizers)


C030 - Detailed drawing - AP

M010 - Material specification - AP

C040 - Design analysis - FI, RCrankshaft

C050 - Non-destructivetesting (NDT) plan - FI

C030 - Detailed drawing - FIConnecting rod

M010 - Material specification - FI

C030 - Detailed drawing - FICylinder and cylinder headwith bolts M010 - Material specification - FI

Compressor C040 - Design analysisDocumentation of torsionalvibration in reciprocatingcompressors, see [7.1]

FI

Seals C030 - Detailed drawingDocumentation for sealingarrangements with materialspecification for seals

FI, R

Table 4 Additional documentation for screw and centrifugal or turbo compressors


C030 - Detailed drawing AP, if > 1 000 kW FI

M010 - Material specification AP, if > 1 000 kW FIRotors with bladesC050 - Non-destructivetesting (NDT) plan - FI

Burst speed rotors withblades C040 - Design analysis Required, if > 1 000 kW FI, R

C030 - Detailed drawing AP, if > 1 000 kW and rotorwith blades FI

M010 - Material specification AP, if > 1 000 kW and rotorwith blades FI

C040 - Design analysis Rotor casing strength FI, RRotor casing

C040 - Design analysisRotor casing containment.Required, if > 1 000 kW androtor with blades

FI, R

Rotor C040 - Design analysis Rotor strength see [2.3.1] FI, R

Seals C030 - Detailed drawingDocumentation for sealingarrangements with materialspecification for seals

FI, R

AP = Approved



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FI = For informationR = Approved on request

1.4 Required compliance documentation1.4.1 For general compliance documentation requirements, see DNV-CG-0550 Sec.4.

1.4.2 For a definition of the compliance document types, see DNV-CG-0550 Sec.3.

1.4.3 Product certificateThe complete compressor shall be delivered with product certificate, tested and inspected as required inTable 5, Table 6 or Table 7 (depending on type).With reference to Pt.5 Ch.6 Sec.1 compressors for nitrogen generator with rating 100 kW or less may bedelivered with product certificate issued by manufacturer.

Table 5 Compliance documents required for reciprocating compressors, including boosters(maximisers)

Object Certificate type Issued by Certification Additional description

Compressor PC Society [4.1.1] Shall include functiontest

MD** Manufacturer

PD Manufacturer NDT ultrasonic test*

PD Manufacturer NDT crack detectiontest*

Crankshaft

PD Manufacturer Dimension control

Connecting rod MTR Manufacturer NA

Cylinder and cylinderhead PD Manufacturer [4.1.2] Pressure test

PC - Product certificate

MD - Material declaration

NDT- Non destructive testing

MTR- Material test report

PD - Product declaration

NA - Not applicable

* Not applicable for compressors < 50 kW

** For compressors with power < 50 kW, MD may be replaced by MTR

Table 6 Compliance documents required for screw compressors





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MD** Manufacturer




Casing

PD Manufacturer [4.1.2] Pressure test

MTR Manufacturer NA



Rotor







NA - Not applicable



Table 7 Compliance documents required for centrifugal and turbo compressors



MD** Manufacturer




Casing

PD Manufacturer [4.1.2] Pressure test

MD** Manufacturer



Shaft


Rotor wheel MD** Manufacturer



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MD** Manufacturer



Blades







NA - Not applicable



or for compressors with power > 1000 kW, MC (Material certificate) by society required



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2 Design

2.1 Materials

2.1.1 The materials used for the components of compressors shall conform to Pt.2 Ch.2.

2.1.2 The crankshafts and connecting rods of reciprocating compressors shall be made of forged steel, caststeel or nodular cast iron.The use of special cast iron alloys or some other materials will be subject to special consideration and shallbe agreed with the Society.

2.1.3 Materials intended for low temperaturesThe compressor is a part of piping system, therefore the materials for gas compressors especially for thoseparts which are in direct contact with the gas, shall be considered with regard to low temperature andchemical composition of the gas. Accordingly, Ch.6 Sec.1 Table 1 and Ch.6 Sec.2 shall be followed.

Guidance note:Typical gases referred to are natural gas (NG), petroleum gas (PG) and other gases with similar chemical composition and lowtemperatures.


2.2 Reciprocating compressors2.2.1 CrankshaftsCrankshafts for reciprocating compressors shall include a safety factor against fatigue failures.Calculation method and safety factor shall comply with a recognised standard.



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Guidance note:For air compressors the diameters of shaft journals and crank pins may be determined as follows:

For refrigerant compressors the diameters of shaft journals and crank pins may be determined as follows:

dk = minimum pin/journal diameter [mm]

D = cylinder bore for single-stage compressors [mm]

DHd = cylinder bore of the second stage in two-stage compressors with separate pistons

1.4 × DHd for two stage compressors with a stepped piston (see Figure 1)

for two-stage compressors with a differential piston (see Figure 1)

Figure 1 Stepped piston (left) and differential piston (right)

pc = design pressure PR, applicable up to 40 [bar]

H = piston stroke [mm]

L = distance between main bearing centres where one crank is located between two bearings [mm]. L shall besubstituted by L1 = 0.85 × L where two cranks at different angles are located between two main bearings, orby L2 = 0.95 × L where 2 or 3 connecting rods are mounted on one crank.

f = 1.0 where the cylinders are in line

For V- or W type:1.2 where the cylinders are at 90°1.5 where the cylinders are at 60°1.8 where the cylinders are at 45°

C1 = coefficient according to Table 8 [–]

Z = number of cylinders

Cw = material factor according to Table 9 or Table 10 [–]

Rm = minimum tensile strength [N/mm2].



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Table 8 Values of C1

Z 1 2 4 6 ≥ 8

C1 1.0 1.1 1.2 1.3 1.4

Table 9 Values of Cw for steel shafts

Rm Cw

400

440

480

520

560

600

640

≥ 680

7201)

≥ 7601)

1.03

0.94

0.91

0.85

0.79

0.77

0.74

0.70

0.66

0.64

1) Only for drop forged shafts

Table 10 Values of Cw for nodular cast iron shafts

Rm Cw

370

400

500

600

700

≥ 800

1.20

1.10

1.08

0.98

0.94

0.90

Where increased strength is achieved by a favourable configuration of the crankshaft, smaller values of dk may be approved.


2.3 Non-reciprocating compressors2.3.1 RotorsRotor strength calculation method and safety factor shall be according to a recognised standard.

2.3.2 Rotor casingRotor casing strength calculation method and safety factor shall be according to a recognised standard.Alternatively the strength may be documented by destructive testing.Such destructive testing (proof test) shall be carried out in accordance with the ASME Boiler and PressureVessel Code, Section VIII, Division I, or other recognised standards.



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2.4 ContainmentContainment for centrifugal and turbo compressors shall be fulfilled for compressor wheel failure at 110% ofmaximum permissible operating speed.For compressors with power over 1000 kW requirements according to Ch.3 Sec.1 [11.1.2.2] shall be fulfilled.

2.5 Piping and arrangement2.5.1 Safety valvesCompressors shall be protected by safety valves for every compressor stage. The safety valves shall be setto open at the design pressure (set pressure = design pressure). For starting air compressors, see also Ch.7Sec.5 [2.2].Screw or displacement compressors may be instead equipped with an overflow valve to lead the gas fromdischarge to the suction sideFor reciprocating compressors where one compressor stage comprises several cylinders which can be shut offindividually, each cylinder shall be equipped with a safety valve.

Guidance note:The design and the set pressure should be sufficiently higher than the working pressure in order to have margins for setting of thesafety valve.


2.5.2 Pressure gaugesEach compressor stage shall be fitted with a pressure gauge with a scale indicating the relevant maximumworking pressure.Pressure transmitter showing the actual and maximum working pressure may be accepted.For reciprocating compressors where one compressor stage comprises several cylinders which can be shut ofindividually, each cylinder shall be equipped with a pressure gauge.

2.5.3 CondensationThe piping to and from air compressors shall be arranged to prevent condensation from entering thecylinders.

2.5.4 For air compressors onlyFor air compressors, the following apply:

— After the final stage, all air compressors shall be equipped with a water trap and an after-cooler.— Water traps, after-coolers and the compressed air spaces between the stages shall be provided withdischarge devices at their lowest points.

— Unless the cooling water spaces of air compressors and coolers are provided with open discharges theyshall be fitted with safety valves or rupture discs of sufficient cross-sectional area. High-pressure stage aircoolers shall not be located in the air compressor cooling water space.Guidance note:Exemption may be granted in case suitability of protecting devices for cooling water casing is verified by testing in the presence ofa surveyor.


2.5.4.1 For oil lubricated air compressorsThe compressed air temperature, measured directly at the discharge from the individual stages, shall notexceed 160°C for multi-stage compressors or 200°C for single-stage compressors. For discharge pressures ofup to 10 bar, temperatures may be higher by 20°C.



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Guidance note:Discharge air temperature of multi-stage compressors may be approved for up to 200°C if it can be shown that the appliedlubrication oil is suitable for this temperature. Specification of oil and documentation of capacity shall be provided by maker.Testing may be required



3.1 General

3.1.1 The certification principles and the principles of manufacturing survey arrangements (MSA) aredescribed in Pt.1 Ch.1 Sec.4 [2.5].

Guidance note:It is advised to establish an MSA with sub-suppliers delivering materials or parts and tested and inspected as required mentionedin Table 5, Table 6 or Table 8 (depending on type).


3.1.2 For material and testing specifications, see Pt.1 Ch.3.

3.1.3 Ancillaries not covered by Table 5, Table 6 and Table 8 and are integrated as part of the compressorshall be checked as found relevant by the compressor manufacturer.

Guidance note:As ancillaries in this contests we mean parts of lubrication and cooling system.


3.2 Inspection of the partsManufacturer's measurement report shall be presented for main items and shall be available upon request forminor components.Manufacturer's survey report shall be available upon request.

4 Workshop testing

4.1 General4.1.1 Function testingFunction testing shall be carried out on each compressor in the presence of a surveyor.The function testing as a minimum shall include the following:

— Safety functions, checking of correct opening pressure for the safety valves— Capacity test, see [4.1.1.1]— Alarms, see Table 11

4.1.1.1 Capacity testA capacity test shall be carried out with the compressor running at design condition (rated sped, pressure,temperature, type of gas, etc.).



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Guidance note:The capacity test may be waived for compressors produced in series and when previous tests have been carried out on similarcompressors with satisfactory result.


4.1.2 Hydraulic pressure testingAll parts subject to pressure of the compressors shall be hydraulically pressure tested (W) to 1.5 times thedesign pressure.The test pressure need not exceed the design pressure by more than 70 bars.

5 Control and monitoring

5.1 General

5.1.1 Control and monitoring shall be in accordance with Table 11.

Table 11 Control and monitoring of compressors

System/Item

Gr 1Indication alarmload reduction

Gr 2Automatic



1.0 Bearings

Temperature HA For shaft power > 1 500kW

2.0 Lubricating oil

Pressure IL, LA Applicable for forcedlubrication

Sump Level IL1) or IR Applicable for splashlubrication

3.0 Compressed medium

Pressure IL See [2.5.2]



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LR = Load reduction, either manual or automatic, with corresponding alarm, either slow down (r/min reduction) oralternative means of load reduction (e. g. pitch reduction), whichever is relevant


1) Dipstick is acceptable as local indicator.

5.1.2 For control and monitoring of cargo refrigeration (for ships having additional class notation RM) seePt.6 Ch.4 Sec.9 [3.4].

5.1.3 For control and monitoring of cargo, fuel, refrigeration and nitrogen plants for ships having classnotation Tanker for liquefied gas, see Pt.5 Ch.7 Sec.13 Table 2.

5.1.4 For control and monitoring of gas power plants for ships having class notation Gas power plants seePt.6 Ch.5 Sec.20 [6].

6 Arrangement on-board

6.1 General

6.1.1 Air compressors shall be arranged and located so as to minimise the intake of oil or watercontaminated air.

7 Vibration

7.1 Torsional vibration

7.1.1 For reciprocating compressors with shaft power exceeding 500 kW, torsional vibration analysis shall bedetermined according to the requirements given in Ch.2 Sec.2.The permissible limits of any component in the system shall not be exceeded.



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8 Installation inspection

8.1 Installation onboard

8.1.1 After installation on board, the compressor and the system to which it is connected shall be functiontested under working conditions. See also Ch.6 Sec.5.

8.1.2 The function test shall include testing of any control and safety functions.

8.2 Vibration

8.2.1 For resilient mounted reciprocating compressors, the vibration shall be observed by the surveyor andconsidered with regards to all connections to the compressor such as coupling, piping etc.The operation of the compressor shall not result in resonance vibrations on the compressor environment.



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CHANGES – HISTORIC

July 2019 edition

Amendments October 2020, entering into force 1 January 2021Topic Reference Description

Sec.3 All requirements related to steering gear for thrusters are now includedin the thruster rules. Ch.10 Steering gear is not relevant for thrustersanymore.Rule requirements are more in line with industry standard, especially forcontrol systems.

IACS UI SC242 rev.2 is implemented.

Sec.3 Figure 1 New definitions are presented, especially for steering gears as presentedin Sec.3 Figure 1.

Sec.3 [1.6] Number of required technical documents is increased, mainly caused bymore clarified list reflecting actual practice.

Sec.3 [1.7] Product certificate for thruster may be replaced by separate productcertificates for steering gear unit and azimuthing unit.

Sec.3 [2] Requirements for operation and arrangement of main functions steeringand propulsion are highlighted and presented in a new subsection.

Sec.3 [2.2.1] It is required two independent thrusters serving both main functionspropulsion and steering, 'steering propulsion units'.

Sec.3 [2.3.2] It is required two independent steering actuating systems for eachsteering gear, as required in IACS UI SC242. Exceptions given forthrusters below 1000 kW installed on non-SOLAS vessels.

Complete revision of rulesfor podded and gearedthrusters

Sec.3 [3.4.5] Extended and detailed requirements to electric steering gear.

Required compliancedocumentation

Sec.1 [1.3]

Sec.2 [1.3]

Sec.3 [1.7]

Sec.4 [1.4]

The subsections have changed name to reflect the common terminologyfor compliance documents, which may include certificates anddeclarations. The terminology is further described in DNVGL-CG-0550.

Changes July 2019, entering into force 1 January 2020Topic Reference Description

Compressor requirementchanges

Sec.4 [1.4.4] Certification requirements for compressors with power less than 50 kWare simplified.

Introduced new requirement on material certificate issued by the Societyfor compressors with power above 1000 KW.

Added Sec.4 Table 5, Sec.4 Table 6 and Sec.4 Table 7 giving an overviewof requirements for various types of compressors.

Part 4 Chapter 5 Changes – historic


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Topic Reference Description

Sec.4 [2.1.3] Introduced new requirements for materials intended for lowtemperatures.

Added guidance note to clarify types of gases.

Sec.4 [2.4] Introduced new requirement on containment for turbo compressors withpower over 1000 KW.

Re-organised content ofcompressor rules

Sec.4 The section has been re-organised to give requirements according tocompressor types.

Sec.2 [8.1] Reference to Ch.2 Sec.6 is added for survey.

Sec.3 [6.1] Reference to Ch.2 Sec.6 is added as applicable requirements.

Requirements forfoundation are moved toCh.2 Sec.6

Sec.3 [8.2] Re-phrased to refer to Ch.2 Sec.6.

January 2017 edition

Amendments January 2018, entering into force 1 July 2018Topic Reference Description

Update of DocReq. Sec.3 Table 2 Deleted 2 rows for C040 -Design analysis for torsional vibrationcalculations and torsional impact calculations (this is covered inCh.2).

Main changes January 2017, entering into force 1 July 2017

• General— Various editorial updates.

• Sec.2 Water jets— Sec.2 [3.1.2]: Ancillaries shall be handled by manufacturer as relevant.

• Sec.3 Podded and geared thrusters— Sec.3 Table 1: Updated definition for steering system.— Sec.3 [1.4.5]: Included control systems in certification.— Sec.3 [2.4.3]: IACS UI SC242 is referred to in guidance note.— Sec.3 [2.4.10]: Revised rules for crash stop with propulsion thrusters. Turning speed requirement of 2rpm with quay test is removed. It is opened up for alternative procedures.

— Sec.3 [2.8.5]: Removed text regarding one pump per thruster.— Sec.3 [1.4.9] and Sec.3 [3.1.2]: Ancillaries shall be handled by manufacturer as relevant.— Sec.3 [2.4.13] and Sec.3 [9.1.1]: Steering gear tests for thrusters are now handled in Sec.3 andreferences to Ch.10 Sec.1 is removed.

— Sec.3 [9.1.7]: Dockside test removed (now a part of SG trial).



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July 2016 edition

Main changes July 2016, entering into force 1 January 2017

• Sec.1 Propellers— Sec.1: Updated text related to hub caps with fins (and cap bolts).— Sec.1 [1.2.5]: Polar and diametrical mass moment of inertia of entrained water to be specified.

• Sec.2 Water jets— New Sec.2 [2.1.4]: Requirements have been moved from guidance note in Sec.2 [2.1.3].

• Sec.3 Podded and geared thrusters— Sec.3 [2.4.3] a): The paragraph has been rephrased to reflect the IACS UI SC242 / MSC.1 Circ 1416regarding steering for thrusters.

— New Sec.3 [2.8.4] and Sec.3 [2.8.5]: Requirements moved from guidance note in Sec.3 [2.8.3].

• Sec.4 Compressors— Sec.4 [4.1.4] and Sec.4 Table 7: Requirement for temperature measurement of compressed medium hasbeen deleted.

October 2015 editionThis is a new document.The rules enter into force 1 January 2016.

Amendments January 2016

• General— Only editorial corrections have been made.



DNV AS

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DNV-RU-SHIP Pt.4 Ch.5 Rotating machinery - driven units

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Transcript of DNV-RU-SHIP Pt.4 Ch.5 Rotating machinery - driven units