How's it done? What are you supposed to have in the cabin? Does it have to be written on the bill of sale when purchasing?

What kind of write-off are you asking about?

If you use the boat for commercial purposes, like fishing charters, joy rides, etc., yes it can be considered a business expense.

If you have a place to sleep, cook, and go to the bathroom, you can write off the interest paid on a loan secured by the boat, as second home mortgage interest(provided you don't already claim two homes). See IRS Publication 936 for more info.

I"ve been writing off the interest on mine for 10 years now. Geez, that means I'll own it in 4 more years.... anyway, I list it on the itemization sheet as "second home/boat" and simply add in the interest.

The qualifications have changed over the years, but they were:

Must be sleeping quarters on board.
Pump out head
Must be able to prepare a meal on board.
Must spend minimum of 10 nights on board

I believe the 10 nights thing has gone by the wayside. And I'm not so sure about the pump out anymore. I figure if they haven't asked me about it yet, they aren't going to.

Good info guys. I have a business but I was referring to as a second house. I may sell the business.
Can you do it at any time or only when it's purchased? What about sales tax? Any way to write it off as well?

Straight from Pub 936:

"For you to take a home mortgage interest deduction, your debt must be secured by a qualified home. This means your main home or your second home. A home includes a house, condominium, cooperative, mobile home, house trailer, boat, or similar property that has sleeping, cooking, and toilet facilities."

No more, no less...the above paragraph alone determines qualifications.

Every year that you pay interest on a loan.

Sales tax can be deducted in some states by way of a new code for 2004. I was able to take advantage of the sales tax I paid for the purchase of my boat in '04.

we write off the interest every year just like it says in the posts above

i wirite off the interest as well.....

So I guess you can only use a primary home and a secondary home. No third, right?