Trolling Motor Size Chart
The most important factor in selecting a trolling motor is size. The following charts will help you determine the proper size trolling motor for your boat.
While there is no "one size fits all" trolling motor for every watercraft, there are two basic criteria for determining a compatible trolling for your boat: thrust and shaft length. Once you've determined your thrust and shaft length requirements using the size charts below, you can select the appropriate trolling motor.
1. Determine thrust
Thrust is arguably the most important factor for selecting a trolling motor. Thrust, measured in pounds (lbs), is the power a motor exerts. The heavier and larger your boat, the more thrust required to move and maneuver it on the water. You want to make sure your trolling motor meets the minimum thrust requirements for your boat. Trolling motors come in 12v, 24v and 36v voltage ratings. Trolling motors with higher voltage ratings produce more thrust.
Use your boat's weight and length to determine the minimum thrust level and voltage for your trolling motor. (You can use the NADA boat directory look up your boat's weight and length based on manufacturer.)
|Boat Weight (lb)||Max Boat Length (FT)||Minimum Thrust Level (LB of Thrust)||Batteries Needed|
|1,500 or less||14'||30||1 battery (12v)|
|2000||17'-18'||40-45||1 battery (12v)|
|2,500||20'-21'||50-55||1 battery (12v)|
|3,000-3,500||23'||70||2 batteries (24v)|
|4,000||25'||80||2 batteries (24v)|
|4,500 or more||25'+||101-112||3 batteries (36v)|
|Note: A good rule of thumb is to have a minimum of 2 lbs of thrust per 100lbs.|
2. Determine shaft length
Shaft length is the second factor to determine for selecting a trolling motor. As a rule of thumb, the foot of the trolling motor (prop) should always be covered by at least 12" of water. Correct shaft length ensures the trolling motor sits at the correct water depth, provides the correct level of thrust, and does not cavitate.
Generally, to determine the correct shaft length needed for your boat, measure the distance from the mounting spot of the bow or transom down to the waterline. Then, take this measurement and add 20" to get the desired shaft length. If you are stuck between two sizes, err on the larger size.
There are a few other factors to consider when determining correct shaft length. If you plan on fishing offshore or in rough water, add 25" to your bow to water line measurement. This will ensure your prop remains submergered in choppy water. If you'll be using a hand controlled trolling motor while standing, add 12" to the recommended transom shaft length. This will allow you raise the motor tiller and improve comfort. (Note: You can also attach a telescoping extension handle to add height instead of raising the motor tiller.)
Use the following tables to get a more accurate shaft length for your trolling motor based on bow to waterline and transom to waterline measurements.
Determining shaft length for bow-mount motors
Determining the correct shaft length for bow-mount trolling motors is more critical than for transom-mount motors, since the distance from the bow of a boat to the water can vary greatly between boat styles and models. Use the following chart to determine recommended shaft length based on bow to waterline measurement.
Determining shaft length for transom-mount motors
Determining shaft length for transom-mount trolling motors is a little easier than for bow-mount motors, since the distance from the transom of the boat to the water doesn't vary as much between boat styles and models. Use the following chart to determine recommended shaft length based on transom to waterline measurement.
3. Find your trolling motor
The following table will help you find trolling motors based thrust and shaft length.
|Thrust(lbs)||Shaft Length(in)||Recommended Motors|