Get the Right Size Trolling Motor

recommended shaft length for bow mounted trolling motors info graphic

By Tom Burden, Last Updated 5/2/2018

What to Look For

Bow Mounted Motors

Bow mounted motors are convenient if you fish primarily in an open bow-rider or on the fore-deck of a bass boat. To prevent damage from groundings, a spring-loaded mount like Minn Kota’s BowGuard 360 allows the motor to swing away on impact. On very small craft or on a light sailboat the trolling motor often doubles as an auxiliary engine and is mounted on the transom where it is operated by a tiller.

Transom-Mount Motors

Transom-mount motors feature brackets that adjust to different angles and heights so the motor’s shaft is immersed at the right depth.

recommended shaft length for transom mounted trolling motors info graphic

Fresh vs. Saltwater

Saltwater motors are protected against corrosion and have better seals on the mechanical and electrical components.

Shaft Length

The standard shaft length is 42". To determine the right length for your boat, measure the distance from where the shaft is mounted on the deck or the transom to the water. Then add 16" (for MotorGuide) or 20" (for Minn Kota) and select the next closest measurement. We recommend longer shafts for operation in rough water so the prop stays about 6" below the surface when the boat pitches and rolls. Fine-tune the motor’s vertical position with the adjustment on the mount.


Trolling motors are rated in pounds of thrust. As a rule of thumb 72 to 75lb. of thrust roughly equals one horsepower or 746W of electrical power. A typical 12V motor that draws 60A consumes approximately 720W. The equation for power is easy: the higher the voltage, the higher the thrust. Trolling motors are offered in 12V, 12/24V, 24V and 36V versions, with the most powerful ones offering more than 100lb. of thrust, powerful enough to move heavy vessels such as pontoon boats. Maximum thrusts at different voltages are approximately 12V/55lb. and 24V/80lb.

Thrust to Boat Length Guidelines graph

The Right Size

Bigger is almost always better. Larger boats need more juice, but we recommend you consider wave action, wind and current when choosing a trolling motor. Erring on the stronger side has its benefits because stronger motors run more efficiently at lower speeds and provide a safety cushion for handling wind, waves and current. We recommend 5lb. of thrust for every 200lb. of a vessel’s gross weight.

Power Consumption

Think about the size of your boat, how much battery capacity you can safely install to satisfy the energy demands of a trolling motor, and whether or not you will be able to charge the batteries when underway. Check the amp draw of the models you have in mind. A 24V model with 54lb. of thrust may only draw 28A, while a 12V model with 44lb. of thrust can draw 36A. The rule of thumb is that larger motors require more battery capacity, and if you fish from dawn to dark with a boat of 16' or longer, you’ll probably want 24V. Serious anglers who spend a lot of time on the water will appreciate a 36V motor.