no tax in St. Martin?
Consider this. If I buy a boat in Florida I pay no Florida taxes when I bring it back to Virgina within 60 days. I do however pay VA tax and personal property tax when I bring it home. Who cares about the tax where you buy it.
As with any foreign purchase getting the proper documentation to remove the boat from that country then bring it into another (any other) is a specific and detailled process that needds professional assistance or at least legal consultation. To register a foreign vessle in the US requires some exacting documentation. A bill of sale alone is not enough.
You could be stuck with no place to go.
Lots of folks leave vessles in the Islands and just fly down to use it. St Martin is in Hurricane zone so insurance is an issue. You would need to get it farther south (Trinidad) to be out of that zone.
There are a hundred different details to this idea you really need to investigate all the angles and costs.