About antifouling.....

[emmanoss]

Good morning to everyone...
I recently bought a 25ft sailing boat (a contest 25 HC), made in 1982 that had antifouling painted last March.... The boat has some grass around the water line and at the centerboard only, and my question is, if the antifouling treatment HAS to be applied EVERY 12 months or it can be delayed......
The other thing is about osmosis treatment. How often is it nessesary to be done?
Thank you and have a nice day!!!

[celenoglu]

In some areas the antifouling might be used for two seasons and in sone areas you need a bottom paint every year. Grass means the antifouling at the water level is not active any more and might mean further growth on the body might be expected in the very near future. It will be a good idea to apply antifouling as soon as possible. The main growth season is the spring and the beginning of summer for fouling.

Osmosis treatment is not a periodical application. If the hull is dry (check with a humidity meter) a protective coat of epoxy can be applied to the hull to retard osmosis (please note that epoxy is better than gelcoat but it also permits some water). If you apply epoxy on a wet hull, the probability of osmosis defect will increase.

If you already have osmosis on your boat there are three options:

1. Do nothing, wait until it starts inside the layers.
2. Open the defective areas, wash them with hot water, dry them and apply epoxy coating. These spots will not be affected from further osmosis but other parts of the boat will.
3. Peel off the gelcoat, cover the boat and wash with hot water. Dry it (might take weeks or months) repair the damaged portions with epoxy and glass fibers. Paint with two coats of epoxy and apply paint.

[emmanoss]

Thank you Celenoglu, you were very helpful. I guess, the dryer the hull is. the better. How many layers of antifouling would you suggest?

[celenoglu]

Most of the antifoulings generally indicate the thickness of paint to be effective. This is the technical point. From a practical point of view, apply at least 3 coats of paint with a roller or at least two coats with a brush.

Again a practical guide: 2.5 liters of antifouling can paint 1 coat for a boat of 30 ft. with a roller. I generally apply three coats. If I am economically not in good condition during antifouling application I apply two coats and apply a third coat to the water level, to the front and back part of the keel and the rudder and to the head of the boat.

[sailingdog]

If you're using an ablative antifouling paint, you really have to apply a couple extra coats at the leading edges and along the water line. These areas get extra wear and that is probably why you have grass growing along the waterline.