Power of Pleasure(1990)

Husband Christoph Clark and Wife Joy Karins go cruising for a day around the bay in their big cabin cruiser with friends and crew. Before long the hot sun has hot and bothered, with the sight of well-tanned bodies, topless in French fashion, lying everywhere, it's causes inhibitions to be forgotten. The husband seduces the nurse, Joy seduces every guy in sight and goes skinny-dipping with Isabelle, before they "share" a shower on deck. Joy's friend Laurie is given a "tour" of the engine room by two of the crew. Finally a screening of a tape of Joy turns into a full blown night of passion that they all will never forget.