That is also a holiday (Boxing Day) which might influence ferry schedules to a degree. What does it cost if you lose a night of accommodations on VG, have to buy a new hotel in STT, get extra taxis, tips, and meals in STT?

I'm a sure thing guy, especially on vacation; that said, my last 3 Cape Air flights all cancelled in the last 4 weeks and I had to buy charters; so that didn't really work out.

The ferries are currently more reliable than the local air options due to staffing.

Good luck.