Land at Princess Juliana Airport (SXM), step onto a private boat, and be on Saint-Barthélemy in about 41 min. No ferry timetable, no overnight on the wrong island — the transfer is timed on your flight.
The public ferry runs on its own timetable and rarely matches an arriving flight; a missed connection means a night on Sint Maarten instead of Saint-Barthélemy.
A private transfer leaves when you land, takes your luggage in one go, and covers the 32 km in about 41 min.