Can a Trolling Motor Shaft Be Too Long? A Guide to Proper Sizing

Trolling motors allow you to cover more water, but proper sizing is critical. If a trolling motor shaft isn’t sized right it will cause problems. So, can a trolling motor shaft be too long?

A trolling motor shaft can be too long. If the trolling motor shaft is too long, you risk the propeller hitting bottom or the inability to stow the motor properly. Too long of a shaft can not only damage the propeller but also the rest of the motor and the environment beneath the water as well.

Read on to learn more about trolling motor shafts. For more information, read further to learn how to shrink a trolling motor shaft.

How Long Should a Trolling Motor’s Shaft Be?

A trolling motor shaft can be too long or too short. Therefore, it is best to find an appropriate length based on the size of your vessel and the water you fish. Additionally, you should factor in your boat’s draft and weight as well. So, how do you find the correct length?

A trolling motor shaft should be significantly longer than the distance between your boat’s bow/mounting point and the waterline. In freshwater, add at least 20 in (50.8 cm) to this measurement. ]n saltwater, add at least 25 in (63.5cm) to this measurement.

Let’s discuss measuring the required length of your trolling motor shaft.

Finding the best length for the shaft is a pretty simple process. Here are some tips that will make it even more straightforward:

Measure in calm water: Establishing an accurate waterline is tricky in choppy water that won’t stop moving. I recommend taking your measurement in calm water first before traveling to choppier water and waves.
Account for additional weight: Various sources of weight will affect your measurements. For instance, bodies and equipment in a lightweight boat can cause a significant dip. Furthermore, you should measure with a full tank of gas to estimate bow rise. On top of all of this, you also need to factor in the weight of the motor and batteries. You are essentially aiming to replicate “real world” conditions as much as imaginable.

Bird hanging out on boat with trolling motor raised up out of the water.

Consider if the motor will hold: When fishing rough water, the propeller will be more inclined to cavitate out of the water when an approaching wave arrives. If you like to fish along the beach or inlets and passes, you may consider a longer shaft model.

Once you get the appropriate measurements for your boat and the waters you’ll be treading, it’s time to find the right shaft.

So, what’s the proper way to measure a shaft? You should measure from the motorhead’s base to the top of the propellor housing, as shown below:

Visual on how to measure shaft length. — Source: TrollingMotors.net: Shaft Length Guide

Another way to check the length of the shaft is to refer to the “rated” shaft length provided by the motor’s manufacturer. Sometimes the rated length is more accurate since all trolling motors get made a little differently.

How Deep Should a Trolling Motor’s Propellor Be in the Water?

By now, you should have a general idea of how to measure the correct shaft length. Still, if you are unsure why I prescribed this method, I can break it down further. Part of the reasoning behind adding the additional 20-25 in (or 50.8-63.5 cm) is the depth requirements of the shaft.

A trolling motor’s propeller should be at least 12 in (30.5 cm) deep in the water. In choppy waters, that amount increases even more. It’s vital to keep the motor’s propeller below the water to avoid cavitation and startling the fish. However, your motor will still function under slight cavitation.

Boy with shark on boat with trolling motor in background.

Wait a minute! If the propeller only has to be 12 in (30.5 cm) deep, why are you adding so much additional length?

Keep in mind that you are not only compensating for below the mounting point but above it as well.

Take a look at this diagram, for instance:

Source: Anchor Travel: How Deep Should My Trolling Motor Be in the Water?

Notice how the motorhead sits 8 inches (20.32 cm) above the mounting area? When you add the extra length to your bow-to-waterline measurement, you are accommodating for above the mount and below. Otherwise, you may invest in a minuscule shaft, and your propeller will pop above water.

You may be wondering, how much cavitation is too much? The goal is to have as little as possible. After all, all those air bubbles will scare fish away.

While you should avoid cavitation, a limited amount will not mess with your motor’s functionality. Just make sure your propellor is not popping outside the water, or your boat won’t go anywhere.

How Do You Make a Trolling Motor Shaft Shorter?

Finding the right shaft is pretty to the point when you are shopping for one or two favorite fishing spots. However, adaptation becomes a more significant concern if you find yourself traveling to new bodies of water. Is it possible to compress your trolling motor shaft when the need arises?

You can make a trolling motor shaft shorter using the depth collar adjustment to change the length. However, suppose you wish to decrease your trolling motor shaft significantly. In that case, you can cut down the shaft with a metal cutter.

Trolling motors often have a depth collar adjustment mechanism that can change the shaft’s length. You can find instructions for operating this mechanism in your manufacturer’s user manual. Here is an example from the Minn Kota Endura Transom Mount Trolling Motor from Amazon.com’s manual:

Source: ManualsLib: Using And Adjusting The Motor; Adjusting The Depth Of The Motor; Adjusting The Steering; Controlling Speed & Direction – MINN KOTA ENDURA C2 User Manual [Page 10]

If you wish to repurpose or significantly curtail your trolling motor shaft, there are ways to accomplish that too. Here is a step-by-step example from KayakDIY. They recommend using the TEKTON 64501 Mini Tubing Cutter from Amazon.com for this project.

Check out their video, and I’ve outlined the steps below as well.

Remove the non-essential components: First, you need to remove any unnecessary parts for this project. In this case, I am referring to the mount and the head. Make sure to take a photo of the wiring inside the head before removing it. You can refer to this photo later if you need to reconfigure the head. These removals will leave you with a bare trolling motor.
Mark the spot where you wish to cut.
Cut down the shaft: The tubing cutter is very easy to use. First, tighten the cutter onto the shaft. Once secure, turn the cutter around the shaft until you notice cuts. Once you see the initial cuts, you can fasten the grip of the cutter even more. Continue to turn the cutter until the two pieces of the shaft disconnect.

Run wires from the discarded shaft: You will notice wires running from the propellor through the shaft. Pull the wires out from the top part that you cut off, and you are all set.

KayakDIY used their new shortened motor to create a motorized fishing kayak!

Can A Trolling Motor Shaft Be Too Short?

If you choose to shorten your trolling motor shaft, you need to be extremely careful. Just as too long of a shaft can cause issues, there are implications from having too short of one as well.

Too short a shaft on a trolling motor can prohibit the propellor from functioning properly. As a result, the movement from the propeller will cause cavitation and scare off nearby fish.

So don’t overdo it! Always make sure you’re sizing the shaft properly for optimal performance.

Final Thoughts

Trolling motors are a great tool that allows us to pull into tight spots and back out when we otherwise couldn’t. But, if you’re going to have one, you need to make sure you’re properly equipped. Proper sizing is essential to get the best use and longevity of the motor.

In short, a trolling motor shaft can be too long if the propeller is digging into the floor of whatever body of water you’re traversing.

It’s also critical to avoid a shaft that is too short. A short trolling motor shaft can scare away fish or limit your motor’s mobility. Therefore, always measure for the proper shaft length when you change boats or go to a new place. Doing so will save you plenty of agony in the long run.,