Many new boaters often ask the question, “what does ‘trim’ mean”? Knowing what it means to trim a boat, and how to properly trim a boat, will improve its performance and fuel economy. Trim is simply the running angle of the boat as it makes way in the water; when we adjust the trim we are either raising or lowering the bow (the front of the boat). Here’s how it works…
Just remember that the boat’s bow will move in the same direction you press the trim button—button up is bow up, button down is bow down.
Negative trim—when the trim is all the way down—is used to help get the boat on plane as it accelerates away from dead in the water. The angle of the propeller thrust will help lift the stern and push the bow down so that the boat rolls smartly up onto the water.
Try to power on plane with the drive trimmed out, and the prop will dig a hole behind the boat and the bow will point skyward, probably blocking your view forward, as the boat struggles to plane. You may get on plane eventually, but you are wasting fuel and putting undue stress on the engine.
Once on plane, it’s time to trim up to raise the bow so that the boat is skimming along over the water, rather than pushing through it.
Eventually, you may over-trim and raise the drive or outboard so far that the prop begins aerating and losing bite on the water—boat speed will decrease even as engine RPM increases. Bump the trim button down a little and the prop will hook back up with the water.
Porpoising, or the bow bobbing up and dow, is caused by over-trimming at cruising speed; there’s no longer enough hull in the water to support the weight of the boat. Either trim down a little until the porpoising stops, or increase boat speed slightly to create more lifting force under the hull. In rough water, especially with a head sea, trimming down will soften the ride by allowing the sharper deadrise of the forward bow to slice through the chop.
An experienced captain gets in the habit of trimming the drive or outboard all the way down every time the boat comes off plane so that it’s in position when it’s time to power back on plane. Automatic trim systems, a feature of many newer boats that can also often be added as an accessory, effectively manage the trim based on boat speed and throttle setting.
Boats powered by smaller outboards may not have a power trim system, but the trim can still be adjusted manually by moving a pin in the motor bracket.