Calculating antifouling, paint required, fouling and osmosis cover

Fouling costs speed and fuel. A fouled hull easily loses a third of its speed and burns proportionally more fuel, so the antifouling coat is not cosmetic, it is a matter of running costs. The area is estimated from length, beam and draught; a keel adds a lot of surface, so keelboats have considerably more wetted area than motor boats of the same length.

For insurance, the underwater hull is above all a question of where the line falls. Fouling, corrosion and wear are conditions that develop gradually, so none of them is a loss event. With osmosis we make an exception: under the Premium tariff, osmosis damage is covered on the basis of a survey for up to 48 months after completion at the yard; standard wordings almost always exclude it, and a repair runs into five figures.

It is a different matter when a grounding damages the underwater hull, or when someone else damages the hull in winter storage. Then the hull cover responds, and a record of how the boat has been looked after helps to draw the line. A maintenance record that logs each coat is therefore more than a nicety.