Long Bay Beach is on the northern shore of Tortola. It is a nice beach, about a mile long stretch. There is a resort and several guest houses on its' eastern portion, the western end offers some quiet and good swimming.
I am not aware of any facilities along this beach except for those of Lambert's , the resort. I do not know whether they are available to non guests. The beach itself is very narrow along most of its' length.
Enjoy your stay on Tortola.