Offshore Support Vessels Design

By: Ahmed Taha Abd El-Mawla

Contents

• Introduction• Design of the vessel • Resistance of the vessel • Construction of the vessel • Weight of the vessel• Intact Stability

Introduction

• The origin of offshore support vessels may be traced to the Gulf of Mexico. where oil exploration first moved offshore in the 1950s.

• Surplus World War II vessels and wooden fishing boats were used to supply offshore rigs

Design and operating capabilities

• Large and open aft deck.• Highly maneuverable, particularly at low speed.• Storage for offshore exploration and production activities:

such as bulk mud and cement, potable water• Wheel house all - round visibility (have forward & aft control) • High engine power for towing operations. • Some OSVs are equipped with big fire pump with monitors for external

firefighting system. • Dynamic Positioning (DP) system is very important for all types of OSVs.

Types of Offshore Support Vessel

• Anchor Handling Towing Supply vessels (AHTS) • Diving Support Vessels (DSV)• Platform Supply Vessels (PSV)• Cable & Pipe Laying Vessels• Standby and Rescue Vessels• Multi-Purpose Service Vessel (MPSV)

Features of offshore supply vessel

Work deck

Anchor roller

Steering gear

Ducted propellerStern TubeTransverse Thruster

Tanks For dry bulk

Deck cranes

Propeller shaftGear boxMaine engine

Life raft

MOB-boat with crane

Storage reel for steel wires for anchor

BridgeFirefighting monitor

Switchboard

Design of vessel • The design of a ship is an iterative process, in which early estimates

are made.• Then repeatedly corrected.• Design and Construction – IMO A.469 (XII)

• Design spiral• Main Particulars

Length overall = 20 mLength B.P. = 19.3 mBreath moulded = 6.66 mDepth moulded = 3.3 mDesign draught = 2 m

Design of vessel • Lines Plans

Before After

• Generation of the hull surface

Design of vessel

• General Arrangements

Design of vessel

Outboard Profile

Below Main Deck

• Preliminary hydrostatic calculations

Displacement 122.9 tVolume (displaced) 119.895 m^3Draft Amidships 2 mImmersed depth 2.015 mWL Length 19.392 mBeam max extents on WL 6.144 mWetted Area 136.187 m^2Max sect. area 7.821 m^2Waterpl. Area 105.717 m^2Prismatic coeff. (Cp) 0.79 Block coeff. (Cb) 0.499 Max Sect. area coeff. (Cm) 0.636 Waterpl. area coeff. (Cwp) 0.887

LCB length -0.158 (+ve fwd) mLCF length -0.504 (+ve fwd) m

LCB % -0.813 (+ve fwd) % Lwl

LCF % -2.599 (+ve fwd) % Lwl

KB 1.333 mBMt 2.41 mBML 23.723 mGMt corrected 3.743 mGML 25.056 mKMt 3.743 mKML 25.056 mImmersion (TPc) 1.084 tonne/cmMTc 1.588 tonne.m

Design of vessel

Resistance of the vessel

0 2 4 6 8 10 12 14 16 18 20 22 240

50

100

150

200

250

300

Resistance Vs. Speed

Resistance

Speed Knots

Resis

tanc

e KN

33.2 KN

0 2 4 6 8 10 12 14 16 18 20 22 240

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

Speed Vs Power

Power

Speed Knots

Pow

er K

WResistance of the vessel =

280 KW

Construction of vessel

• Calculation in detail according to the ABS rules:Offshore Support Vessels 2016-Part 3 Hull Construction and Equipment

• CHAPTER 2: Hull Structures and Arrangements

Midship Section6 .667 m

0 .5  m 1 .65  m

L.75*50*6

T.150*130*123 .3  m

Deck  7 .5mm  PL.

Side   7 .5 mm  PL.

Bottom  8mm  PL.

3D Model Representation

Weight of the vessel

Light weight Estimations

Steel weight 25 tonOutfitting Weight 3 tonMachinery Weight 5 tonTotal Light Weight 33 ton

Dead Weight

• Dead Weight = displacement – light weight

Freshwater 18.00 tonDry bulk cargo tanks (cement) 15.00 tonFuel oil 2.00 tonOil cargo 38.00 tonFreshwater cargo 15.00 tonWeight for persons 2.5 ton

Intact Stability• Loading Conditions1. Light weight Condition 2. Full load Condition 3. Vessel with 10% of consumables ,departure condition.4. Vessel with 10% of consumables ,arrival condition. 

Equilibrium

Draft Amidships m 1.960Displacement t 118.3Heel deg 0.0Draft at FP m 2.012Draft at AP m 1.909Draft at LCF m 1.958Trim (+ve by stern) m -0.103WL Length m 19.399Beam max 6.123LCB. (+ve fwd) m -0.018LCF. (+ve fwd) m -0.479

Full load Condition KB m 1.309KG fluid m 1.749BMt m 2.447BML m 24.444GMt corrected m 2.006GML m 24.003KMt m 3.755KML m 25.752Immersion (TPc) tonne/cm 1.075MTc tonne.m 1.464Max deck inclination deg 0.3033Trim angle (+ve by stern) deg -0.3033

= 3.755-1.749 = 2.006

Light weight Condition 10% departure condition10% arrival condition Draft Amidships m 1.018Displacement t 33.00Heel deg 0.0Draft at FP m 0.657Draft at AP m 1.379Draft at LCF m 1.071Trim (+ve by stern) m 0.722KB m 0.769KG fluid m 1.839BMt m 3.481BML m 54.615GMt corrected m 2.410GML m 53.544KMt m 4.248KML m 55.346Trim angle (+ve by stern) deg

2.1329

Draft Amidships m 1.898Displacement t 112.6Heel deg 0.0Draft at FP m 1.775Draft at AP m 2.021Draft at LCF m 1.906Trim (+ve by stern) m 0.245KB m 1.279KG fluid m 2.005BMt m 2.500BML m 24.951GMt corrected m 1.775GML m 24.226KMt m 3.779KML m 26.228Trim angle (+ve by stern) deg

0.7251

Draft Amidships m 1.402Displacement t 62.82Heel deg 0.0Draft at FP m 1.311Draft at AP m 1.494Draft at LCF m 1.409Trim (+ve by stern) m 0.183KB m 0.973KG fluid m 1.927BMt m 3.064BML m 37.415GMt corrected m 2.110GML m 36.461KMt m 4.037KML m 38.387Trim angle (+ve by stern) deg

0.5406

Large Angle Stability

0 10 20 30 40 50 60 70 80 90 100 110 120

-0.5

0

0.5

1

1.5

2

Full Load GZ - θ CurveGZInitial GMMax GZ

Heel θ deg.

GZ m

Range of Stability

θ 𝒇

Initial GM

Max GZ

θ❑

CRITERIA REQUIRED

Area between 0 and angle of maximum GZ

3.1513

Area from 30 to 40 deg. 1.7189

Maximum GZ 0.200

Angle of maximum GZ 15

Initial GMt 0.150

full load Condition

23.7920

9.9358

1.005

38.2

2.006

light weight Condition

43.9612

11.2493

1.499

51.8

2.410

10% departure condition

32.4616

10.2960

1.161

46.4

2.110

10% arrival condition

18.6107

8.7455

0.882

35.5

1.775

IMO A.749 (18) ch4,5 Offshore supply vessels

20 40 60 80 100 120 1400

0.5

1

1.5

2

2.5

3

3.5

Cross Curves KN

0 deg KN m10 deg KN m20 deg KN m30 deg KN m40 deg KN m50 deg KN m60 deg KN m70 deg KN m

Displacement (ton)

KN m

KN Values Cross Curve of Stability

Upright Hydrostatics

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

20

40

60

80

100

120

140

0.0001 0.91823.887

9.267

17.5129.17

44.42

61.99

81.22

101.6

122.8

Draft Vs. Displacement

Displacement t

Draft (m)

Displacemen

t (ton)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

20

40

60

80

100

120

140

0.049.205

20.035

32.794

48.108

65.547

81.586

89.8297.129

101.504105.652

0.045

10.123

22.036

36.005

52.632

71.788

90.55

101.766

112.464121.427

130.268

Draft Vs. Area

Wetted AreaWaterpl. Area

Draft (m)

Area ( m^2)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

5

10

15

20

25

0.038 0.948 1.8952.842

3.7884.451 4.925

5.399 5.749 5.946 6.144

8.836

11.379

13.072

14.679

16.23317.779

18.922 19.053 19.173 19.28519.392

WL LengthBeam max

Draft (m)

(m)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.034

0.395

0.3730.355 0.343 0.356 0.384

0.417 0.4460.477

0.5

0.068

0.829

0.7650.722 0.694

0.681 0.6960.735 0.759 0.777 0.79

CpCbCwpCm

Draft (m)

(m)

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