How Do I Set My Torque Trim Tab on My Outboard Motor?
by Kyle McBride
Torque trim tabs help to counteract the effects of torque, or wheel-walk, on the vector of the boat. Wheel-walk is a phenomenon that is created by differing water pressure at the top and the bottom of the propeller. As the propeller rotates through the water, the pressure at the bottom of the propeller is greater than the pressure at the top. This creates greater drag at the bottom than at the top and makes the propeller try to "walk" sideways through the water. This makes a right-handed prop -- a prop with clockwise rotation -- move laterally through the water, and makes the stern of the boat swing to the right, making the boat turn to the left when underway. Counter-steering with the helm will not correct this and will only succeed in making the entire boat move at an oblique angle to the direction that the bow is pointing.
Step 1
Test drive the boat at full speed with the steering amidships -- in the center -- to determine how much wheel-walk is occurring.. Observe how much the boat turns. Boats that turn opposite the prop rotation need more angle on the tab. Boats that turn the same direction as the prop rotation need less angle on the tab.
Step 2
Stop the boat to adjust the tab. Remove the plug on top of the anti-ventilation plate with the screwdriver to gain access to the trim tab bolt.
Step 3
Hold the trim tab firmly in position by hand and loosen the trim tab bolt. Rotate the tab in small increments in the appropriate direction, then firmly tighten the bolt. Reinstall the plug and test drive the boat again. Observe the boat's handling and make further adjustments as needed.
Tips
- The goal of this process is to make the boat track straight ahead when the steering is dead amidships -- dead center -- at full throttle. Continue adjusting the tab until this is achieved.
- There is no magic formula to getting this adjustment right on the first try. Many factors, including boat design and ballast placement, can affect the boat's handling and each boat and motor combination is different.
- Unfortunately, the only way to adjust this is through trial and error. Making small adjustments and testing the motor is time consuming, but will prevent you from over-adjusting and forcing you to waste more time backing up and readjusting.
Things You'll Need
- Mechanic's tools
- Large flat screwdriver
Warnings
- Driving a boat that is badly out of trim is inefficient and potentially dangerous. It can cause you to waste fuel "going sideways" and cause the boat to meet oncoming waves with the broad side of the boat, instead of the much stronger bow section. The waves can cause the sides of the boat to collapse inward and can cause uncontrollable and unpredictable rolling motions that can damage equipment and injure crew, including the possibility of passengers being thrown overboard.
