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When your aluminum boat begins to bounce as it accelerates, it's called "porpoising." Because your boat is light, it's jumping around like a porpoise, leaping up and diving down. Not only is this situation uncomfortable for everyone aboard, it's hazardous. If the bow dives under the water, there's a chance it will keep diving, driven by your motor, until it can't come up. Fortunately, the cure for this may be no more complicated than having someone hold the bow down.
Slow your boat down. Porpoising begins as you motor picks up speed and raises your boat's hull from the water, reducing the amount of hull in the water -- which means there's too little hull in the water to support the boat.
Trim the motor down until the boat stops bouncing. Changing the trim of the motor -- and thus, the axis along which power is applied to the boat, keeps more of the hull in the water as the boat begins to plane.
Move passengers or cargo toward the bow of the boat a little at a time. This has the same net effect as trimming the motor; it holds the bow down. Generally, only a small amount of weight needs to move forward, since the change acts like an off-center seesaw, with the balance of the seesaw at the boat's transom and the end of the long arm of the seesaw located in the bow.
Mount trim tabs on the stern of the boat. Trim the tabs downward under acceleration, to change the speed at which the bow portion of the boat's hull begins to leave the water.
Add a "wing," a hydrofoil, to the top of the anti-cavitation plate on outboard motors. The hydrofoil acts like a single, fixed trim tab.
- If you're in an aluminum boat that's small enough to porpoise, wear a personal flotation device at all times.