Sounds like a reaching strut to me. Does the sheave end have a kind of "beak" sticking out? Look aof a ring or mound of some kind on each side of the mast below the gooseneck. The pole end goes on there and the beak rests on your guy. Not legal for one-design and you won't have time for it on a bouy race, but it'll reduce your guy loading on a long offshore reach.
