Problem with ants in a boat is that they make a nest deep down in crevices and areas not accessible by normal air flow. It would be extremely difficult to get the poison vapors down into these areas unless every floorboard, cabinet door and access panel was opened and fans were placed to blow the poison into such places.
- - The "bait" type poisons seem to work better as the ants themselves take the poison back to their home nest.
I'm in Grenada as well and I have found ant poison at Hubbards in the Food Fair plaza by Rick's Cafe... It's not always available but try there. Just last weekend a neighbour was telling me she wipes a bit of Avon's Skin So Soft around the edges of her countertops to repel ants - haven't tried it myself yet!