Here's another thought or two... I'm guessing the addition of the "Knee" (bracket between bottom and transom) on power boats, even the very small ones is what makes it okay to put a 15 horse on there and bounce along. My 25 plus year old 13 foot Gregor aluminum has always had the motor attached. Used to be an ancient 115 pound 15hp, now an 86 pound 15hp. Several sets of tires and many miles... "Built like a Monty - very strong!" My reason for light is beautiful, easy is better, is because of problems with shoulders. It almost killed me to lift the last foot or so of the Johnson 6hp (70 pounds) up to the stationary motor mount on the M-17. My 17 had the motor attached for 12 years before I got her. And apparently towed over several Oregon Mountain passes on many occasions. The prior owner scoffed when I asked him to carry the motor separate when he was kind enough to deliver her to me. I can find no damage and the new owner, when I sold her, who is a lot more sailboat savvy than I, says she's great. I guess I'm wondering what the manufacturer of sailboats (any brand) would need to make it okay to carry the motor on the transom. Just the knee brace sounds too easy, or it would have been done by now... Perhaps a part of it is in tradition, rather than construction. Bill