IIRC it has to be registered someplace else, not simply kept out of the state, in order to exempt it from sales and use tax. You won't owe any sales since there's no sale
in Florida. You will owe use tax instead, something like 6-1/4? percent plus any county tax.
But you can easily get all the details from the Florida DMV and tax departments, all online and official.
If you don't have someplace else to legally register the boat and operate it out of state for whatever that time period (6? monhts?) then don't even ask, just pay the use tax and import
the boat. And of course, there may be import
tariffs as well.