GPS is absolutely not required for a BVI charter. Navigation is as easy as it gets, the paper
charts are very good, and the briefings before the charter cover the few danger areas.
My suggestion, with over 40 years experience sailing in the islands, is to forget the
GPS and other gadgets and enjoy the charter. It's a wonderful place to learn about just limin' :-) Afterwards you can return to the pressure cooker.
Bill