I lived aboard in St. Martin for most of about 5 years.
Swell from Northeast is much less terrible than swell from northwest. You are likely picking up your boat at Anse Marcel marina, so the bay at Anse Marcel is beautiful and pretty protected. Lots of turtles and a great beach. You might spend a day - or two - there. If St. Martin is a clock, Anse Marcel is about midnight. If you go out of that bay and navigate anti-clockwise, you come to Grand Case at about 11 o'clock - Yyou'll be traveling with the swell behind you, much nicer than otherwise. LEAVING ANSE MARCEL BE AWARE OF THE SHOAL RUNNING OUT FROM THE WESTERN SHORE straight toward Anguilla. GIVE IT A WIDE BERTH. Grand Case is a wonderful place to visit If you tuck in well, intpo the southeast corner of the bay. You may choose to spend a couple of days there. Great beach, lively main drag at night, amazing dining both cheap and expensive. In a swell the dinghy dock may be a bit sporty. If you continue anti clockwise you come to Happy Bay, which will be exposed, but is a very beautiful day stop, you may end up with the beach to yourself or almost to yourself. The next bay is Friars, where you can tuck in tight to the north eastern shore and enjoy great swimming, and another amazing beach. After that, continuing anticlockwise, you come to Galisbay and Marigot Bay. You can tuck in at either of these as well, Galisbay at anchor, Marigot on a ball - get one up front near theferry port. You have to pay for the ball at the Gare Maritime just at the dinghy dock. It is possible to anchor in Marigot Bay, but in these conditions anchoring outside the mooring field may be uncomfortable.
If all else fails, take the boat into the lagoon from the French side. It's calm as can be.
In a northeast swell, you will not enjoy going to St. Barth's, it will be what we sailors call "shitty."
You are allowed to cross the border in your dinghy, but if you take the big boat across the border, you must check out of the French side and check into the Dutch side. Not worth it.
There is a facebook group Saint Martin/Sint Maarten Cruisers and boaters. I am an administrator. In the files section you can find a cruising guide I wrote a couple of years ago. Everything is more or less still current except check-in procedures.
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