We use these 20' gunwale tie downs from West Marine:
INDIANA MARINE Tiedown at West Marine
They are heavy duty SS and have a nice set of hooks. Just throw the long end over the dingy, grab from undernieth with a boathook, clip on the other half, and tighten the ratchet. Very sucure if you use two. I don't sail with the outboard attached. Too heavy when heeled way over.