Posted by JimM on October 17, 2002 at 08:10:19:
In Reply to: Re: Tuffy problems.. posted by Dominik on October 17, 2002 at 02:02:41:
Don't forget, porpoising can also be caused by a "rocker" in the bottom. This is a convex (downward) curve in any bottom longitudinals, looking from the side. If you place a good straightedge along the keel, or in any positions parallel to the keel, there should be even contact for the aftmost 1/3 or so of the boat's length. The opposite, a "hook" or a "hogged" keel tends to cause nose-diving and a lot of spray (I had one of them once!).
Turn the boat over, and place the straightedge at a number of locations while marking high or low areas. This generates a "map" of the contour to help you figure out where to fill.
Rocker can be corrected by filling near the transom with thickened epoxy (use micro balloons for light weight). Hook can be similarly corrected inbetween the high areas. I wouldn't plane anything off the plywood bottom - it's already too thin! Make those longitudinal lines as straight as you possibly can for best performance.