Part 1 Steering Gear

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University of Stratchclyde

Faculty of Engineering

Department of Naval Architecture and Marine Engineering

Part 1: Steering Gear

Course no.: NM 315

Hossein Ghaemi

Sem. I, 2010/11


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Contents

PART ONEPART ONESteering Gear

Auxiliary Power Machinery

PART THREEPART THREE

Deck Machinery

PART FOURPART FOUR

Part 1: Steering Gear Marine Engineering I2


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Contents

1.1. Requirements

1.2. Control Unit

1.3. Power Units

. . .

1.3.2. Rotary Vane Type

. . .

. . a cu a on o eer ng ear orque



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Role and Elements

Control equipment

Transmission to the rudder stock



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Requirements

International Convention for the Safety of Life at Sea (SOLAS), 1974

1. Ships must have a main and an auxiliary steering gear,arranged so that the failure of one does not render the otherinoperative.

2. The main steering gear must be able to steer the ship atmaximum ahead service speed and be capable at thisspee , an a e s p s eepes serv ce raug , o pu ngthe rudder from 35 on one side to 30 on the other side innot more than 28 seconds.

3. The auxiliary steering gear must be capable of being

brought speedily into operation and be able to put the rudder more than 60 seconds with the ship at its deepest servicedraught and running ahead at the greater of one half of the


max mum serv ce spee or no s.


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Requirements cont.

4. It must be possible to bring into operation main and auxiliary.

5. Steering gear control must be provided both on the bridge ,where the main steering gear comprised two or moreidentical power units there must be two independent control

.

6. Tankers, chemical carriers and gas carriers of 10 000 GT or

steering gear must be arranged so that loss of steeringcapability due to a single failure in one of the power actuating

. ,seizure of the rudder actuators, must be regained in not morethan 45 seconds.



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Control Unit

Reaction of servo and as a result reaction of rudder de ends on the:1. Dimensions of the servo (so-called step-volume),

2. Cross sectional area of connecting pipes between cut-off slider and servo

3. Feed oil ressure



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Control Unit cd.

)()( 21 tQtQ =

)()( tyAtQ PS &=

ptAtQ =

2)()(

lowup ppp =

2

)()( 021p

tptp ==

)()()( 0 txKtxpb

ty S=

=

& KsY

sG SS == )(

)(


PS


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Control Unit (cont.)

deg7

deg3.2 max


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Ram Type

1. Two-ram

2. Four-ram forks

Arms

Swivel

a rudder stock in order to

provide the leverage to

turn the rudder

cross ea



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Arm forks



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Variable displacement pumps



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A bypass valve is combined with spring-loaded shock valves which

Safety control

In moving over, the pump is actuated and the steering gear willreturn the rudder to its original position once the heavy sea has

.

A spring-loaded return linkage on the tiller will prevent damage to the

control gear during a shock movement



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Moving the floating ring or slipper pad of the pump, causes a pumping

Operational aspects

action. Fluid will be drawn from one cylinder and pumped to the other,thus turning the tiller and the rudder.

.is required, for instance in confined waters, both pumps may be in use.

The pumps will be in the no-delivery state until a rudder movement is.

A return linkage or hunting gear mounted on the tiller will reposition thefloating lever so that no pumping occurs when the required rudderang e s reac e .

During normal operation the steering gear should be made to move atleast once ever two hours to ensure self lubrication of the movinparts.

No valves in the system, except bypass and air vent, should be closed. The replenishing tank level should be regularly checked and, if low,

refilled and the source of leakage found.


, .


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Rotary Vane Type .

The rotoris able to move in a housing which is solidlyattached to the ship's structure.

and the vanes in the housing. These chambers will varyin size as the rotor moves and can be pressurized since

sealing strips are fitted on the moving faces. The chambers either side of the moving vane are

connected to separate pipe systems or manifolds. Thusby supplying hydraulic fluid to all the chambers to the left

chambers on the right, the rudder stock can be made toturn CCW.

Three vanes are usual and permit an angular movemento : e vanes a so ac as s ops m ng ru ermovement.

The hydraulic fluid is supplied by a variable delivery.

A relief valve is fitted in the system to preventoverpressure and allow for shock loading of the rudder.



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Vane-type steering gear.


(Red indicates pressurised oil.Green indicates excess oil.)


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Steering gear room


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Steering Gear



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Actuator Type

The gear is made redundant on one rudder by.

Cost-effective and reliable solution.

ewer n er ace sur aces on oar ecause eactuator's anchor brackets can be welded

.actuator steering gear is less tolerance-criticalfor installation.



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Capacity Comparison


Brown Brothers Rolls Royce Production


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Calculation of Steering Gear Torque

omogeneous ow

:angle of attacks: span width (s>>c)

r

V: constant velocity of fluid far before the rudder

D: drag force (in the direction of the flow)

P: total force (acts at about e~ 0.25c),

-



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Rudder forces are made dimensionless by the stagnation pressure 22

1 V

LC = N=

r

r

D

AV21

r

N

T

AV2

21

r

DAV

2

21

=r

TAV

2

21

=

2222

TNDLP +=+=

+=

+=

sincos

s ncos

DLN CCC

= sincos LDT

Part 1: Steering Gear Marine Engineering I28 = sincos

LDT

CCC


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2

Ar : projected rudder area:

+

= 251ppr

BLDrA

pp

Dr : draft

Lpp : ships length between perpendicularsB : beam

This can be applied only to rudder arrangements in which the rudderis located directly behind the propeller.

or any o er ru er arrangemen an ncrease n e ru er area y- at least 30% is required.



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eN=Me: Moment about the front (or nose) of the rudder

cAVC

r

eMe

=2

21

eC

eNC NM =

=

2ccr2

N

r

NAV

2

21

=

M

Cc

ee=



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Mrs: Moment about the rudder stock

)( aeNMrs =

sAR=Geometrical aspect ratio

Ac r=

sAR

2

=r



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The lift, drag and moment coefficients (CL, CD and CM) of symmetrical NACA

(National Advisory Committee for Aeronautics) wing sections for 0.06 t 0.18



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1.4

ar a on o , rag an momen coe c en s

CL

CD

1

.CM

0.8

fficients

0.4

0.6Co

0.2

0 5 10 15 20 25 300

Angle of attack, deg.


Part 1 Steering Gear

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