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How to Measure Trolling Motor Shaft Length

You may think that the horsepower of your trolling motor is the only thing that matters to have a proper, complete cruise with your boat. But that couldn’t be further from the truth. Although horsepower does play a crucial role in this, the shaft length is just as important. After all, the last thing you want to happen is to lose a good catch. Measuring the shaft length is important for everyone using the boat for fishing.

With the correct shaft length, there will be no noisy cavitation bubbles. These would only end up scaring fish away and your day would be ruined.

If you don’t know how to measure the trolling motor shaft length, we will tell you all about it below.

Why Should You Measure Trolling Motor Shaft Length?

How to Measure Trolling Motor Shaft Length FeaturedWith all this fuss about measuring the trolling motor shaft length, you certainly want to figure out why is it so important. You will see that if you’re a fisherman, you will be more than happy that you considered this type of measurement.

Basically, if you measure the motor shaft length, it will make sure that your boat’s shaft is long enough, which will allow the propeller to stay submerged about 12” under the waterline. This applies to multiple fishing conditions. Furthermore, it will prevent the propeller from coming out of the water while you’re in the middle of your usual operations.

At the same time, there’s something to keep in mind regarding shaft length – while it should be long, it shouldn’t be too long either. If it’s longer than necessary, it may make it difficult for you to stow, and that’s one of the last things you want.

How Can You Measure Trolling Motor Shaft Length?

Measuring the shaft length is not that difficult. The first thing you have to do is put the motor on the ground and find out its shaft length. You can do that by using a tape measure and do the measurements starting from the base of the head and going down to the propeller housing. Pay attention to the inch measurement.

Transom or Bow Height Measurements

You also have to measure the transom or bow weight, as it’s just as important as taking your motor’s measurements. If you make sure to take these measurements, it will help you buy the right motor that suits your boat. Here’s how to measure the bow height:

1. Check the Transom

The first thing you will have to do is check out the bow or transom of the boat. This will allow you to determine the mounting location. After that, put a flat object on that spot. It needs to be hanging over the edge of your boat, so hang it properly.

2. Measure the Vertical Plane

Now, use something like a plumb line or yardstick to measure the vertical plane. Do so according to the vertical plane of the surface of the boat, the flat object’s bottom, and the water. As such, you will get a vertical measurement of the waterline, at least approximately. Round up to the closest inch after drawing an imaginary vertical line.

3. Get the Approximate Length of the Shaft

Make sure to find out the approximate length of the boat’s shaft. For instance, you may want to use a 36-inch shaft for a transom mount motor or a 42-inch motor shaft for a 16-inch waterline.

Bear in mind that when it comes to bow mount motors, you will have to pay more attention to the shaft length and how you pick it. Basically, more movement will be made on the water, and not on the transom. Considering bow-to-water distances are not always the same, you have to do your best to pick the right shaft length.

So, find out the amount of space between the waterline and the horizontal mounting point of the bow. Measure it, and extend the measurement by 20”. Once you obtain this number, you should know that the shaft length you need will be equal or greater.

For rough motor fishing, you should extend the recommended length with 5”. This will ensure the propeller stays submerged. Meanwhile, if you are steering a hand-controlled motor while standing up, you should extend the length of the transom by 12”. Steering will be less uncomfortable and difficult.

Tips for Measuring Trolling Motor Shaft Length

Tips for Measuring Trolling Motor Shaft LengthAlthough measuring the trolling motor shaft length is not the most difficult thing in the world, you still need to do everything you can to take correct measurements. That being said, extra tips are always welcome, and we have some for you:

  • Always ensure you take the measurements when the water is calm. This will help you get an accurate read.
  • For proper results, you should try measuring while the tank is full of gear, fuel, or anything else for that matter. This will allow you to figure out how much the bow rise will be affected. After all, you need to measure under actual conditions, so you can make sure the boat will work properly.
  • Be sure to account for the additional weight directly over the boat’s bow. If the boat is light and you’re in it, there will be a greater dip than expected.
  • The trolling motor battery should be considered as well when it comes to weight, so add that to the motor weight too. If you have a 24v motor and 12v batteries, it will all weigh as much as an adult.

Final Thoughts

Taking the right measurements for the trolling motor shaft length is more important than you think. This is why we wanted to offer some tips to make sure you will do it the right way. Hopefully, our article was helpful, and the advice above will ensure everything is done correctly.

About Peter Richardson

Peter Richardson decided that he needs to balance out the sedentary lifestyle of a software developer by getting out there more. He found passion in none other than – boats. This website represents everything he learned along the way. Finding the right equipment for your boat is no easy task, and that is what Peter’s articles aim to help you with.

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