Movie about a capsized boat. a married couple and the husband's brother

Does anybody know the name of a movie, in which a couple, and the husband's brother, go sailing, and the an accident happens, in which they are capsized?

The movie is from the 70's or 80's 

it seemed like "based on real events"

I recall that in the end a text on the screen explained that the 3 survived but that the husband's brother had to be committed to a mental institution.

Any help is appreciated.