[sailingfool]

I believe many states call the tax a "use" tax not a "sales" tax although it usually is applied at the time of sale.
If you use a boat in a state with a use tax, expect to pay the use tax, sooner or later.

(The following is re my personal MA experience)

Tax officials are wise to attempts to duck their use taxes and enlist harbormasters, marine patrol officers, and town personnel in organized search for tax dodgers. Don''t expect to not get caught.
When you get caught, you will be subject to interest and penalties on the max tax that could have been due. If you manage to duck a use tax for 3-4 years, expect to pay twice the original tax when caught. You would need to be able to conclusively prove the use tax could not be due to avoid it, the onus of proof is on you.
If you want to enjoy a boat in a state with a use tax, pay the tax and enjoy your boat in peace...otherise, at least in MA, they will get you and you will pay big.