I agree with Hud. Proper inflation of the tubes is important. I have a soft-bottom with an inflatable keel
. If the keel
isn't rigid, the motor
will cavitate at higher rpm's.
Try different settings on the motor
tilt (as Hud suggested), and also try re-distributing weight in the dinghy
. Sit farther forward (attach a tiller-extension if necessary).
Perhaps investigate "Dolfins" or some other brand of planing fins for your motor.