boat plowing

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brothers14

Recruit
Joined
Feb 15, 2009
Messages
3
i own a 1985 14ft brothers with a 40hp yamaha man. t/t .similiar to whaler. have a problem with the nose plowing into the water at 3/4 throttle and above the faster i go the more it wants to start lifting the transom out of the water i have it trimed out as far as it will go without cavitating. the cavitation plate is even with the bottom of the boat. i am not sure what the best approach to fixing the problem would be. lower motor a little? hydrofoil? just not sure where to start. thanks for any suggestions.
 
Frank Acampora

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: boat plowing

Take a straightedge and look for a "hook" in the bottom. A hook is a concave section due to pressure of rollers or bunks at or near the stern. It acts like the flaps or elevators of an airplane and at speed will generate lift, forcing the bow down.
 
B

brothers14

Recruit
Joined
Feb 15, 2009
Messages
3
Re: boat plowing

was under the impression the more you trimed it out the more lift in bow and less you trim lower the bow .

if i have a hook in the boat what is the best remedy/repair to correct the problem
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: boat plowing

If you have hook in the bottom, you either live with the boat's performance or repair the hook, by ripping out the floor, straightening teh hull and repairing the stringers.

First check to make sure the motor's antiventilation plate is even with the bottom of the transom. If the motor is too deep in the water, this can contribute to the nose dive. If you have power trim and tilt, triming the motor up should lift the bow somewhat.

My speedboat used to plow water. It had a aluminum plate bolted to the transom for strength, and this plate hung down 2" below the transom bottom. This had the effect of forcing the nose to dive at anything above 1/2 throttle.
 
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