Page 157 - Ship Construction.DJ Eyres 6Ed

Ch14-H8070.fm Page 146 Wednesday, October 18, 2006 6:56 AM
146 Ship Construction
building berth or a building dock, lifted into place and joined. Rather than
erecting 100 to 150 units at the berth or dock they may only have to place
and join as few as 10 to 15.

Joining Ship Sections Afloat

Owing to the enormous increased in size of bulk carriers and tankers,
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some shipyards with restricted facilities, building berth or dock size in
particular, have resorted to building the ship in two halves and joining
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these afloat.
Where the two sections are to be joined afloat extremely accurate fit up
of the sections is aided by the possibilities of ballasting the two ship halves.
The two sections may then be pulled together by tackles; and for the finer
adjustments hydraulic cylinders may be used, extremely accurate optical
instruments being employed to mark off the sections for alignment. One
method adopted is that where a cofferdam is arranged in way of the joint, a
caisson is brought up against the ship’s hull, and the cofferdam and caisson
are pumped dry. To balance any tendency for the vessel to hog during the
pumping of the cofferdam it is necessary to shift ballast in the fore and aft
sections. Once the spaces are dried out welding of the complete joint may
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be undertaken, the resulting weld being X-rayed to test the soundness of
such a critical joint. On completion of the paint scheme in way of the joint
the caisson is removed.
A similar method makes use of a rubber ‘U’ form ring rather than a caisson
which needs modification for each ship size.
If a dry-dock is available the sections may be aligned afloat and even
welded above the waterline, the rest of the joint or the complete joint being
secured by strongbacks. The welding of the rest or the whole joint is carried
out in the dock.

Further Reading
‘Samsung’s mega-block revolution’ Surveyor, Fall 2005 edition, American
Bureau of Shipping publication.
‘Welding mechanization and automation in shipbuilding worldwide’ Richard
Boekholt Abington Publishing.