How to Measure Trolling Motor Shaft Length? (Bow & Transom Mount Guide)

Little things which we often tend to ignore usually play a vital role… and a similar case is with the shaft length. Correct trolling motor shaft length can provide an optimal thrust as the propeller remains under the water all time.

A short shaft can make the propeller come out of water in the middle, and a longer shaft length causes the motorhead to touch underwater hazards, weed, rocks, etc. So, measuring your shaft length is equally important as choosing your trolling motor.

Measuring the Shaft Length

To measure your shaft length, you need to take the measurement starting from the base of the motor head to the top of the propeller housing using a tape. However, some factors and exceptions vary from model to model.

Factors while choosing the Shaft Length

To ensure your trolling motor doesn’t cavitate, which would otherwise create noise that would make fishes spook away… you should follow some steps in choosing the accurate shaft length for your trolling motor, which depends on certain factors as below.

1. Location – You can either install your trolling motor on the bow or mount it at the rear end or can also place it on the central motor. It plays an important role in deciding your shaft length as you would require a longer shaft length if you want to place your trolling motor on the bow as the height is higher than the rear end.

2. Water conditions – If you want to fish sessions to be in a lake or river, you will not come in contact with too many waves… so you can choose a short shaft length. If you prefer fishing in bigger waterbodies, you may face turbulent waves which would make your boat rise… so you would require a longer shaft length.

3. Boat Types – The type of boat also plays a crucial role in deciding your shaft length. Sailboats, zodiacs, and canoes would require short shafts while pontoon boats and Carolina Skiffs boats will need a longer shaft length. The boats with a high transom or barges would need an extra-long shaft length for your trolling motor.

Measuring Bow Mount Shaft Length

Choosing bow mount shaft length is more critical as compared to transom mount trolling motors because the bow to water distance changes from boat to boat. To measure the length of your shaft, measure the distance from the top of the deck to the surface of the water, horizontally.

After measuring the distance, add 20 inches to it and get a shaft length equal to or longer than this measurement. There might be changes based on the below conditions:

  • If you fish in rough water, often then add 5 inches to this measurement to ensure your propeller is always submerged in the wind.
  • If you frequently deal with saltwater conditions, add 25 inches from bow to waterline distance to get minimum shaft length.
  • For a hand-controlled motor, steering adds 12 inches to the transom lengths to make your steering comfortable.

Measuring Transom Mount Shaft Length

Transom mount shaft length choice is quite easy compared to bow mount. To measure the shaft length for transom motors, measure the distance from the mounting location or spot down to the waterline, and you can choose it according to the below measurements.

  • If the distance between the transom mount to the waterline is 0” to 10,” choose a 30-inch shaft length.
  • If the distance between the transom mount to the waterline is 10” to 16”, choose a 36-inch shaft length.
  • If the distance between the transom mount to the waterline is 16” to 20”, choose a 42-inch shaft length.
  • If the distance between the transom mount to the waterline is above 22,” consult the factory for the shaft length.

Tips for measuring Trolling Motor shaft length

Although the process of measuring the shaft length for your trolling motor is quite easy, the below tips would make your task easier.

  • For boats having lightweight, your bow will dip more in water, so do a check for additional weight on the bow.
  • If you have to choose between two shaft lengths, go for the longer one.
  • Measure your shaft length in calm water if it would make the measurements precise and easy.
  • Add the weight of the trolling motor and its batteries also while measuring shaft length as it won’t be less to ignore.
  • When you measure the shaft length, make sure all your gears are in place and the tank is full of fuel that would give you a fair idea of how much your bow will rise.
  • Make sure your top of the motor is submerged at least 12 inches under the water to prevent cavitation and measure proper shaft length.


Using the depth collar adjustment, you can adjust the shaft depth upward when your shaft is long, but if you pick up a short one…you will not have a choice.

So make sure you measure the trolling motor shaft length precisely for better experience while fishing.

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