What can i write off if im living on a boat?

[Coleen3]

If it qualifies to be your home, you may write off any "mortgage" interest.

You can deduct interest you pay on a loan secured by your main home (where you ordinarily live most of the time) and a second home. A second home can include any other residence you own and treat as a second home, and can be a mobile home, house trailer, recreational vehicle, or houseboat that has sleeping, cooking and toilet facilities.

This is an itemized deduction similar to a home mortgage. If your total itemized deductions (Property Tax, Mortgage Interest, Charitable Donations and State Income Tax) don't add up to more than the standard deduction for your filing status. More info about your situation would be needed to know for sure.