Sorry if this has been said, as I may not have read all the mail on this subject, but it is pretty easy to see whether your hull is a true displacement hull or a semi-displacement hull: look at the transom. Does it go down into the water? If it does, it is not a true displacement hull, and you can forget about getting all that efficiency. If the hull rises out of the water before meeting the transom it is very likely a displacement hull. If they meet at the waterline, it is probably a displacement hull. The Krogens and Willards and some custom designs are the only ones I know of that are true displacement hulls for sure. The rest will drag water behind them, and we pay to pull it around. You can run the formulas backwards to figure out what your effective prismatic coefficient is, but we semi-displacement boats are effectively perty chubby. On my boat (34 ft, ~30 ft LWL) the practical hull speed seems to be about 7.5 Kts for ~80 HP (at the engine), and an increase of 30% in RPMs and HP doesn't buy much extra speed, maybe a knot or so. So it acts sort of like a displacement hull, but it isn't. If it were, the hull speed would only be about 6 Kts. The designer apparently felt the extra knot and a half at the top end was worth the efficiency hit, and I think this is pretty common in trawlers. Jason Kovatch CHB 34 Everett WA