Page 332 - Ship Construction.DJ Eyres 6Ed

Ch27-H8070.fm Page 321 Wednesday, October 18, 2006 7:01 AM
Corrosion Control and Anti-fouling Systems 321
against a wide range of fouling organisms, also they were able to be chem-
ically bonded to the acrylic backbone of the paint system. When immersed
in sea water a specific chemical reaction took place which cleaved the
TBT from the paint backbone, resulting in both controlled release of the
TBT and controlled disappearance or polishing of the paint film. Unfor-
tunately, it was found that the small concentrations of TBT’s released,
particularly in enclosed coastal waters, had a harmful effect on certain
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marine organisms. This led to he banning of TBT anti-fouling paints for
pleasure boats and smaller commercial ships in many developed countries
and the introduction of regulations limiting the release rate of TBT for
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
antifouling paints on larger ships. The International Convention On
The Control Of Harmful Anti-Fouling On Ships, 2001 subsequently
required that –

(a) ships shall not apply or reapply organotin compounds which act
as biocides in anti-fouling systems on or after 1 January 2003; and
(b) no ship shall have organotin compounds which act as biocides in
anti-fouling systems (except floating platforms, FSU’s and FPSO’s
built before 2003 and not docked since before 2003)
ึ
(Note! Organotin means an organic compound with one or more tin atoms
in its molecules used as a pesticide, hitherto considered to decompose
safely, now found to be toxic in the food chain. A biocide is a chemical
capable of killing living organisms).
Anti-fouling paints subsequently applied have generally focused on
either the use of copper-based self polishing antifouling products, which
operate in a similar manner to the banned TBT products, or the use of the
so-called low-surface-energy coatings. The latter coatings do not polish or
contain booster biocides, instead they offer a very smooth, low-surface-
energy surface to which it is difficult for fouling to adhere. When the vessel
is at rest some fouling may occur but once it is underway and reaches a crit-
ical speed the fouling is released.

Painting Ships

To obtain the optimum performance from paints it is important that the
metal surfaces are properly prepared before application of paints and
subsequently maintained as such throughout the fabrication and erection
process. Paints tailored for the service conditions of the structure to which they
apply, and recommended as such by the manufacturer, only should be applied.

SURFACE PREPARATION Good surface preparation is essential to
successful painting, the primary cause of many paint failures being the inad-
equacy of the initial material preparation.