> I can understand why a hull has a bow-down trim force from a driving sailing rig but what exactly causes the stern to squat under power? If the hull was simply towed from a bow tractor instead of pushed from under the stern by a prop would the same thing happen? The prop(s) produces a velocity of the water under the boat and therefore reduces the pressure sucking the boat down (Bernouli's equation). That will not occur by towing the boat. You could almost think of it as pumping the water out from under the boat, but that is not physically correct. ***************************************** Bill Fleenor, Ph.D. Research Engineer Dept of Civil & Environmental Engineering University of California - Davis *****************************************