[TrueBlue]

I don't believe there is a clear distinction between s/v and s/y. Both labels are clearly used for vessels which can be powered solely by their sails. I know that the term "yacht" was originally used to describe any light and fast sailing boat - used to convey "important" persons. I assume that is how the word attained a snobbish status. It later became to mean any vessel, sail or power, used for pleasure and racing.

Personally, I would never call an optimist dinghy a sailing yacht, but it certainly is a sailing vessel. Therefore, aside from the commercial use notion, perhaps size would be a distinguishing factor.