I'm looking at a 21' cedar on oak inboard hull that is similar to a maine lobster boat; round chine, skeg built. How does one determine how much power it takes to drive a hull like this (semi-planing?) to a certain speed. Currently the engine is a defunct 55hp ford diesel, that according to the previous owner would only give 10 knts. If there isn't a rule of thumb perhaps someone could recomend a book on the subject.