I would be very cautious bringing a 50' monohull into Eustacia Sound. The western entrance channel by Saba Rock has several coral heads as you pass north of BEYC that are at 6-7 ft depth. The ocean entrance channel near ONB also has some coral heads that are at 7-8 feet and possibly shallower (note that some of the approach markers are missing). If you safely make it into Eustacia Sound, then you could anchor in Long Bay and dinghy to the ONB reception dock.

We have eaten at the ONB Beach Club about a dozen times. The food and service is excellent as you might expect. The facilities are beautiful. You need to call for a lunch/dinnqer reservation and obtaining one will depend on how many owners and guests they have on-island or if the are running a private function (same as with Peter Island resort). The pool and resort facilities are reserved for guest use, though I recall you could pay a healthy day use fee.

ONB plan was to eventually make the Beach Club restaurant private for owners and guests, and open the marina restaurant for the public. The marina took damage and looks to be a ways off from opening.