Most trolling motor makers recommend running the motor deep enough that the top of the motor housing sits about 12 inches below the surface. That keeps the prop from drawing in air, which makes noise, wastes thrust and spooks fish. Go deeper in rough water so the motor does not come out of the water as the bow rises, and raise it in shallow water to keep the prop off the bottom.
Signs your trolling motor is too shallow
- Prop noise, surface churn or a sucking sound.
- Thrust drops off and the boat yaws in waves.
- The motor breaks the surface as the bow pitches.
- Spot-lock or GPS anchoring struggles to hold in chop.
Signs it is too deep
- The motor hits bottom, weeds or stumps in shallow water.
- Extra drag when stowing or deploying in shallow areas.
- The shaft collar is at its limit with no room to adjust.
How to set the depth
- Deploy the motor and loosen the depth collar.
- Slide the shaft until the top of the motor housing sits roughly a foot below the surface at rest.
- Tighten the collar and check it in the conditions you fish most.
- Readjust for rough water or shallow flats.
Depth and shaft length go together
You can only set the right depth if the shaft is long enough. Measure from where the motor mounts to the waterline; a taller bow, rough water or standing to fish all call for a longer shaft. Motor makers publish shaft length charts based on that measurement; see what size trolling motor do I need? For boat types, see jon boat and pontoon trolling motors.
Transom-mount motors
Transom-mounted motors follow the same rule. Because the stern sits lower than the bow, a transom motor usually needs less shaft for the same depth.
Kayaks and small boats
On kayaks and canoes the mount is close to the water, so a short shaft is enough, but the same principle applies: keep the prop fully submerged with some margin for waves and paddler movement.
Depth affects battery life
A motor that ventilates works harder for the same speed, which shortens run time; see trolling motor battery life. If the motor still underperforms at the right depth, see trolling motor troubleshooting and trolling motor props.
Motors we list
Bow-mount motors such as the Minn Kota Terrova 80 ($1,899.99) and Riptide Maxxum 70 ($999.99) are offered in different shaft lengths; check each listing. Browse trolling motors.
More guides: trolling motors for center consoles · trolling motors for bass boats.
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