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Measures for Reducing Hull Resistance

Anti-fouling Coatings


Traditional antifouling type known as CDP (Controlled Depletion Polymer) is high rosin based that dissolves slowly in seawater. The useful lifetime of CDP paints is usually limited to 36 months. This can be extended by regular underwater scrubbing to remove the leached layer and rejuvenate the paint film but the effectiveness of such cleaning may be limited with respect to time.
Two main high-performance polymer-based tin-free SPC (Self Polishing Co-polymers) technologies in current use are namely metal acrylate co-polymers and silyl acrylate co-polymers. The performance of certain current copper acrylate SPC products are understood to be at least equivalent to TBT-SPC products (TBT-SPC products are banned) that were in use prior to 2003. 

While the above mentioned two types of antifouling coatings have biocides release properties, it can only be expected that the trend for increasing legislation in this area will eventually lead to removal from the market some of the biocides that are in current use. So the Silicone FRC (foul release coating) has become commercially attractive. It is believed that the highly significant additional benefit of FRCs over most biocidal antifouling technologies is the benefit to the ship owner in terms of the fuel saving through reduction in hydrodynamic drag.

Hull Cleaning and Propeller polishing



Friction resistance of the hull is increased due to the marine growth on the hull and the propeller. This deteriorates the water inflow into the propeller and increases the friction losses of the propeller. Industry uses a rule of the thumb that every 25 micrometer increase in hull roughness causes power demand to rise by 2-3%. A worst case of 40% increase in power requirement has been stated to have been observed.

Underwater cleaning is accomplished by a team of divers with manually operated scrubbers that have rotating brushes or pads. Some service providers use Remote Operated Vehicles (ROV) and this does not require diver man hours. Propeller polishing is carried out and roughness is measured as per the Rubert comparator gauge.


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