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Adjusting the Trim on a Motor Boat

2 minutes read
03 Aug, 2023
News & Advice
By Bryony Edwards

Adjusting the Trim on a Motor Boat

Understanding boat trim is essential for improving performance and fuel economy. Trim refers to the running angle of the boat as it moves through the water, and it involves adjusting the bow's position. Remember, if in doubt you can always a professional boat maintenance service take a look!

Here are five simple steps to effectively trim a boat:

  1. Control Trim with the Toggle Button: Most boats have a toggle button on the control lever or dash to adjust the trim.
  2. How Trim Works: Hydraulic rams are used to change the angle of the outboard motor or sterndrive gearcase and the propeller shaft angle relative to the boat's transom. This adjustment can range up to about 20 degrees.
  3. Neutral Trim: When the boat is on plane, and the prop shaft is parallel to the water surface, the trim is considered neutral or zero. In this state, all the propeller force pushes the boat forward.
  4. Pressing the Trim Button Down: When the trim button is pressed down, the gearcase moves closer to the transom, resulting in negative trim (about -6 degrees from zero). This lifts the stern of the boat, pushing the bow down like a teeter-totter.
  5. Pressing the Trim Button Up: When the trim button is pressed up, the gearcase rotates away from the transom, and the propeller shaft points downward. This pushes the stern down and lifts the bow.
Remember, pressing the trim button up lifts the bow, and pressing it down lowers the bow.

To adjust your boat's trim properly:

  • Use Negative Trim for Planing: When accelerating from rest, use negative trim (trim all the way down) to help the boat get on plane. The propeller thrust will lift the stern and push the bow down, aiding a smooth transition to plane.
  • Trim Up While on Plane: Once the boat is on plane, trim up to raise the bow. This allows the boat to skim along the water surface, reducing drag and improving efficiency.
  • Watch for Over-Trimming: Be cautious not to over-trim, as this can cause the prop to lose grip on the water, decreasing boat speed even as engine RPM increases. Adjust the trim button down slightly to regain traction.
  • Dealing with Porpoising: If the boat exhibits porpoising (bow bobbing up and down) at cruising speed, it means the trim may be too high. Trim down slightly to stabilise the ride or increase boat speed to create more lifting force under the hull.

Manually Adjusting a Boats Trim.

For boats without a power trim system, manual trim can be achieved by adjusting a pin in the motor bracket:
  • Locate the Pin: In the motor bracket, you'll find four or five holes for the pin. The pin's position determines the outboard's running angle.
  • Adjusting Manually: With the outboard not running and the boat stationary, move the pin to different holes to find the best trim setting. This may require some trial and error, but aim for efficient planing, slight bow lift at speed, and good handling.
By understanding and properly adjusting boat trim, you can optimize your boat's performance and enjoy a more enjoyable and efficient boating experience. And remember, if in doubt, ask for expert advice from your friendly local boat dealer! The team at Burton Waters are always happy to explain the more technical aspects of boating to new boaters. Or you could take one of our boating courses with our RYA certified boating coach!

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