Having the right shaft length on your trolling motor is absolutely crucial if you want it to work correctly.
This is especially true for the motors mounted on the boat’s bow, as the distance from the bow to the waterline can vary greatly from boat to boat.
In this article, you’ll learn about the necessary steps you need to take to get the correct shaft for your motor.
Why the Shaft Length Is So Important
Thrust or power delivered by your trolling motor is essential, but it is only one factor that will affect your boat’s performance. All this power will amount next to nothing if your trolling motor is not submerged deep enough.
Selecting the right shaft of your trolling motor is absolutely vital. The shaft must be long enough for the propeller to stay submerged at least 16″ below the water line regardless of water and weather conditions.
You don’t want the propeller to get out of water in choppy waters or/and sucking in air from above the waterline when it is not deep enough. It will cause noise, loss of power and can shorten the life of your motor.
Choose Where to Mount Your Motor
First, you will need to figure out where it will be placed.
The bow is the most common location, followed by the transom or rear of your boat. Bow mounted motors will almost always have a longer shaft as they are usually higher than any other place on your boat.
Measure the Distance to the Waterline
As a rough guide, you will need to measure the distance from your chosen mounting location to the waterline. If it’s the bow, go to the bow of your boat with a tape measure and unwind it until it reached the water level.
You will then need add around 20 inches to know the shaft length you need.
It is important that you take your measurements when your boat is fully loaded with gear. If possible, take into account the weight and the location of batteries. On a light boat, it is incredible how much of a difference weight distribution can have.
Also, make sure that you measure the distance to the waterline when the water is calm. Otherwise you readings won’t be accurate.
Shaft Length for Transom Mount Motors
If you want a trolling motor that mounts on your transom, things are usually less complicated. This is because most boats have transoms at a similar height.
Minn Kota recommends the following shaft length for different transom heights:
- 30″ shaft for transoms up to 10″ high
- 36″ shaft for transoms up to 16″ high
- 42″ shaft for transoms up to 20″ high
Shaft Length for Pontoon Boats
For most popular pontoons, a shaft of 60 inches (150cm) will be sufficient, but you will need to take measurements and calculate the right length for your ‘toon.
If you’re stuck deciding between a shorter and longer shaft version, it’s usually safer to go a little longer.
Shaft Length for Engine Mount Motors
Engine mount trolling motors are fixed to the cavitation plate of outboard motors. Before you buy the trolling motor, you should check if the plate is deep enough under the waterline. There should be a minimum of 13 inches of submersion for the trolling motor to function correctly.
Longer Shaft for Rougher Water Conditions
If you use your trolling motor on larger water bodies with a chop and larger waves more common, then it is good to pick a longer shaft.
Choppy waters will move your motor up and down, close to the waterline or even above it. This will result in the loss of thrust and potential damage to the motor’s propeller.
So if you’re not sure which shaft length to choose of the same trolling motor model, pick the longer one. It will be a much safer choice.
Shortening the Existing Shaft
Sometimes you end up with a trolling motor with a shaft that is too long. It may stick out too high, which can be annoying.
What should you do?
It is relatively easy for many popular trolling motor models to shorten the shaft that is too long. Many YouTube videos are showing how this can be done.
It is important to note that such alteration will most likely void your motor’s warranty, so do it only if you absolutely have to.
Frequently Asked Questions
Can a trolling motor shaft be too long?
This is usually not a problem, as a shaft that is too long can always be pulled up or trimmed so that the motor is not too deep under water. If your trolling motor sticks out more than necessary, and you find it annoying, it’s usually possible to shorten your trolling motor’s shaft.
However, we usually advise against it, as you might want to use your trolling motor on a different boat in the future. It’s much harder to make your shaft longer once you shorten it.