Sailboats can be treated as a second home if they have sleeping, eating, cooking, and toilet facilities. There is a requirement that you spend some number of nights sleeing onboard (I believe it is a minimum of 10 nights but you''ll need to verify that number.) If you qualify the interest on your boat loan is deductible. If you itemize then I think the state sales tax is deductible as well. Marina fees and maintenance does not count.