Conversion of tanker into h lift lheavylift vessel

OFFSHOREDAGEN 2009John Riis og Reidar Berthelsen

This is Inocean

Background

Project: Basic design for conversion of six of Suezmax tankers (Split series) to Heavylift vessels

Client: Frontline Management

Project start: January 2006

MSA Approval: 1.april 2006!

Front Marble (Courtesy of Frontline Management AS)Front Marble (Courtesy of Frontline Management AS)

What is a Heavylift vessel?

Scope of work

• Complete class documentation all diciplines

• Conversion specification• General arrangementGeneral arrangement• Lines plan• MSA drawings new-built cargo

part• Steel design for modifications• Steel design for modifications

on existing part• Welding plan • Ballast system

Ai d d i k• Air vent and drain tank system• Electro, New main switchboard

documentation • Intact and damaged stability

Main challenges

• Execution time!!!• Design basis not settled g• Inexperienced yard • Structural integrity of aft section of shipStructural integrity of aft section of ship• Damage stability• 100% Tank filling100% Tank filling

Existing vessel

Conversion concept

Design Particulars

• L.o.a 216,86 m• L.b.p 207,93• Beam moulded 44,5 m• Depth moulded 14 m• Design draft 10,5 m• Submerged draft 23 m• Deck submersion 9m• Deckspace 130 x 44,5m• Deckload 20 t/m2Deckload 20 t/m2• Displacement at

design draft 76.434 MT• Speed Over 15 knots• Cargo capacity 35-40.000 MT

Keppel Fels V design:• Length Hull 71 3 m

Designed to transport JackUp rigs

Length Hull 71.3 m• Width Hull 63,4 m• Depth moulded 7.6 m• Leg length 131.0 m• Weight 14-15000 MT• Frame spacing 1.83 m

260 t 260 tC ibbi bl k

Design load from Jack Up rig 260 t 260 t• Cribbing blocks

6x0.3x0.3m• Max 100 cribbing

blocks• Min long spacing

1 751.75m• Min Transverse

spacing 4.0m• Max 2 on each side

of CL

Key Issues:• Shear capacity• Section modulus of

deck longs.dec o gs• Over pumping

pressure

High tensile steel in High tensile steel in g

LBHD and CLBHD

g

LBHD and CLBHD

200t 200t 200t 200t 200t 200t

Point load (Governing loadcase)

200t• Max point load 200t• Point loads to be placed on

1x1m pads• Max 11 pads on one trv fr.

200t 200t 200t 200t 200t 200t

Key Issues:• Deck plate crushing• Buckling of web plates• Buckling of LBHD.

Mild steel

Vertical stiffeningVertical stiffening of trv. Web

Mi i i l t l t

Aftship structure

• Minimize plate replacement• Use buckling stiffeners where possible

Avoided replacement of LBHD plating in aft ship, with use of torsion box and disconnected 3rd. pl. dk.

D k di t dTorsionbox for re-distribution of

Deck disconnectedforces

Reinforcement of aftship

Buckling stiffeners

3rd. pl dk before conversion

BallastingSequence

Stability Ballasting Sequence

8.0

9.0

10.0

GM decrease due to further deck immersion (AWL d )

Topping of tanksSMALL MARGINS!!

4.0

5.0

6.07.0

GM

flui

d

decreases)

Aft part of cargodeck immersed, tanks in use=partly filled

Cargodeck completelyimmersed

00

1.0

2.0

3.0

4.0

GM (Fluid)Min GM

Start to fill DB5

0.010 11 12 13 14 15 16 17 18 19 20

Draft Midship [m]

Construction sequence

Step 1

Demolition and assembly of new vesselStep 1Separation of bow from vessel.Ready for merger with new midship

.

Foreship in dock

Step 2

Demolition and assembly of new vesselp

Merging foreship and new midship

.

Foreship and new midship

Step 3

Demolition and assembly of new vesselStep 3Removal of old cargo section.Ready for merger with new midship and fore ship

Supports

.

Supports

Matching of hullMatching of hull curvature

Aftship in dock

Seatrails

Submerging test

Submerging, first water on deck T=14m

Submerging, T=23.0m, 9m water on deck

Ready to deballast

Lessons Learned

• Focus on one niche, and translate this to design criterias.

• Global strength analysis of hull girder, key to arrive at simple strengthening concept.

• Project success in Cosco shipyard depends on the site team.

• Dedicated small team, is an effective model for fast track execution.

• Conversions also benefit from ”series effect”

Questions?

C t f D k i LtdCourtesy of Dockwise Ltd