Calculating antifouling, paint required, fouling and osmosis cover

Calculating the paint required starts with the wetted area, worked out from length,

beam and draught; the calculation allows about ten square metres of coverage per litre and two

coats.

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. Osmosis is a special case: standard wordings almost always exclude it, a few policies cover it on the basis of a survey for a limited period after completion at the yard, 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.

Worked out for your type of boat

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