Page 335 - Ship Construction.DJ Eyres 6Ed

Ch27-H8070.fm Page 324 Wednesday, October 18, 2006 7:01 AM
324 Ship Construction
for ship use below the water-line. Suitable corrosion-inhibiting paints for
ships’ bottoms are pitch or bitumen types, chlorinated rubber, coal tar/
epoxy resin, or vinyl resin paints. The anti-fouling paints may be applied after
the corrosion-inhibiting coatings and should not come into direct contact
with the steel hull, since the toxic compounds present may cause corrosion.
(b) Water-line or Boot Topping Region Generally modern practice
requires a complete paint system for the hull above the water-line. This may
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be based on vinyl and alkyd resins or on polyurethane resin paints.
(c) Superstructures Red lead or zinc chromate based primers are com-
monly used. White finishing paints are then used extensively for superstruc-
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
tures. These are usually oleo-resinous or alkyd paints which may be based on
‘non-yellowing’ oils, linseed oil-based paints which yellow on exposure
being avoided on modern ships.
Where aluminium alloy superstructures are fitted, under no circum-
stance should lead based paints be applied; zinc chromate paints are gener-
ally supplied for application to aluminium.

CARGO AND BALLAST TANKS Severe corrosion may occur in a ship’s
cargo tanks as the combined result of carrying liquid cargoes and sea water
ballast, with warm or cold sea water cleaning between voyages. This is par-
ึ
ticularly true of oil tankers. Tankers carrying ‘white oil’ cargoes suffer more
general corrosion than those carrying crude oils which deposit a film on the
tank surface providing some protection against corrosion. The latter type
may however experience severe local pitting corrosion due to the non-
uniformity of the deposited film, and subsequent corrosion of any bare
plate when sea water ballast is carried. Epoxy resin paints are used extensively
within these tanks, and vinyl resins and zinc rich coatings may also be used.

Further Reading

Anti-Fouling Systems – International Convention on the Control of Harm-
ful Anti-Fouling Systems on Ships 2005 Edition IMO Publication.
‘Paint terminology explained’, The Naval Architect, June, 2003.
‘Paints and Coatings Technology’, The Naval Architect, June 2005.

Some Useful Web Sites

www.imo.org see under ‘Marine Environment’ – ‘Anti-fouling systems’
www.jotun.com see under ‘Technical Papers’ – ‘Marine Coatings’
see under ‘Products’ – ‘Cathodic Protection’