If you have 'sweet-loving' ants aboard, Terro works very well. It's a liguid, sweet (apparently) that attracts worker ants. They sample it and take some back to the Queen. Usualy it kills the Queen and then the colony goes away. If you have spiders or other insects, find a Gecko and turn it loose tn your boat. If you have roaches, try Boric acid mixed with evaporated or condensed milk to a paste consistency. Put the mixture in bottle caps all over your boat interior. 'Chinese chalk' also works on roaches.
If you have termites, you'll probably have to have the boat 'tented' and a very toxic gas released in the tent. It takes 24 hours. Don't try this yourself; hire a qualified exterminator.