i recently installed higher horsepower engines in my boat; to keep the same shaft line the new engines had to be positioned a few inches forward of the original engine location. on sea trials we were accelerating to near full throttle when "the bow fell into a hole" and water/spray went over the fly bridge. it was scary! what happened?
Two things changed; shifting the new engines forward moved the longitudinal center of gravity (LCG) forward which caused the running trim angle to reduce. Second, increased propulsion horsepower achieved an increase in top speed; this increase in speed caused further reduction in running trim angle. Thus, at the resulting reduced trim angle, the forward portion of the hull bottom most likely became wetted where the buttocks curve upward which developed a suction pressure. The bow was pulled down suddenly by the force developed by suction pressure.
It may be possible to relocate fixed weights, such as batteries and/or generators to move the LCG aft to correct this problem. Otherwise you may need to seek professional help from experienced hydrodynamic specialists.
