Re: bilgekote over poly
The resin used to make the boat passes all the same testing and more, it doesn't really need to be protected. Does the paint stop these products from contacting the resin… sort of, Just like plastic fuel tanks don't leak, but some components in the fuel still migrate through and escape, it's no different with paint, except that paint is a much thinner and poorer barrier. Even the best 2 part paints aren't recommended for continuous use underwater because they frequently fail, yet gel coat and resin can survive for decades under water (yes some boats blister, but that's a small percentage, and we can get into that part if you want)
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Water is one of the most difficult substances to protect against, there is nothing that is really water proof, there are only varying degrees of water resistance. Epoxy is far more water resistant than polyester resin or paint, but it needs several layers (10+ mils) to be a very good barrier, paints go on at about 3-5 mils.
What it comes down to on many of these decisions is not the facts, but what makes you sleep well at night. If you feel that paint will help, then paint all the surfaces bellow the deck, it doesn’t cost that much and you will feel like you did a better job. I don’t try convincing people to do things one way or another unless it may cause problems for them in the future. This is one of those things that has no real downside other than the cost and time.
Again I am only talking about areas that are never seen again after the floor goes down, engine compartments, open bilges, storage areas and such, all look much better when they are gel coated or painted.
