Maxipoint - I believe that the French side, while part of the EU, is not part of the EU for tax purposes, i.e. the European VAT will not be due upon importation; but this is an area where one really shouldn't look at the internet
for advice but get professional consultation since the ramifications can be quite costly if one gets it wrong. I was always worried about clearing into the French islands with my VAT-not-paid boat and a passport from an EU country. I know they'll hit you upon entering the EU but I've never heard of any case in the Caribbean
where they hit the owners for VAT.
Addendum - just checked, St. Martin (and the other overseas departements of France) doesn't belong to the VAT zone of the EU, but they do have their own taxes
so you would really need to get expert advice, and any taxes you do pay don't go towards your VAT debt upon taking the boat to the EU.