I'm looking for the title of a movie
and I don't have much to go by.
At a guess it was prior to 1990 at least.
It revolved around a yacht, likely a mono-hull and a group of men
and women, probably mainly in their 20-30's.
A specific thing that I remember from it (turn away now if you are sensitive) was that one of the male actors did this thing were when he was about to make love to the girl (this happened with a number of girls), he pulled out his knife and sliced up their leg thus cutting off their bikini bottoms.
Can't remember much else!