The substantial attention given during recent years to the possibility of bunker savings by using more sophisticated bottom treatment systems has, to a large extent, ended in a discussion of the efficiency of various antifouling types and especially selfpolishing and reactivatable antifoulings. According to Jotun Marine Coatings, which has marketed selfpolishing antifouling types (Takata LLL) for many years, this type of modern antifouling is a part of the total answer.
Jotun feels it is necessary to consider the total concept, which Jotun calls Underwater Hull Surface Management (UHSM). When studying the complex problem of friction between underwater hull and seawater, a number of factors should be considered. Roughness can be caused by a variety of problems including corrosion, flaking, blistering, faulty application, etc. Step one in UHSM is eliminating this roughness by sandblasting back to bare steel (SA 2½).
A Jotun study, showing the relationship between bunker savings achieved and the payback period of the capital invested in the blast cleaning, reports that maximum payback period of the extra investment is 13 months. More likely, Jotun states, it would be closer to 4 months, and return of the extra capital invested as high as 75 to 250 percent. That study involved a 280,000-dwt ship, with an investment of $545,000 in sandblasting and a more sophisticated primer system.
The self-polishing antifouling, such as Jotun's Takata LLL, does not leave a porous skeleton as the toxicant is chemically bound to the resin so the paint film slowly dissolves in the seawater. During drydocking, it is sufficient to clean the hull and apply new coats of antifouling directly over the old.
The reactivatable type of antifouling, such as Jotun's Seamaster, is based on different principle. This is built up the same way as the traditional longlife antifoulings. With this type, however, the skeleton can be removed periodically by a special underwater brushing machine. As a result, the service life of the antifouling film can be prolonged extensively—up to 4-5 years—between each drydocking depending on the original film thickness. By undertaking reactivation prior to drydocking, there will be no porous skeleton left on the surface when the ship is in dock. New antifouling can then be applied directly on top of the old the same as the selfpolishing antifoulings.
In both cases, either by using a selfpolishing antifouling or a reactivatable antifouling, it is possible to maintain the original smoothness of the underwater hull. Experience, Jotun reports, shows it has been possible to maintain smoothness on the underwater hull for as long as 11 years.
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