With technology continuing to be developed, the original concept of trolling motors has been expanded. For example, the latest generation GPS drive units can be routed on a specific course or hold the boat stationary without the need to drop anchor.
Choosing the length of a trolling motor shaft is an important decision. If the shaft length is too short, it may not extend deep enough below the water surface, and if it is too long, it could be damaged on a submerged reef and be more prone to bending caused by the forces it is subject to.
The shaft length you choose will determine the size of the trolling motor.
This article explains how important it is to choose the correct shaft length unit for your boat and provides information on long-shaft trolling motors to help ensure that you choose the correct, most appropriate product.
🤔 How To Select The Trolling Motor Shaft Length
Having made the expensive mistake of purchasing the wrong length Trolling Motor Shaft in the past, I have developed some of my own thoughts, which I hope will help you with your decision.
From experience, I can tell you that selecting the correct or proper shaft length for the boat is essential. You will experience problems if it is the incorrect length for your application.
Several factors must be considered when choosing the optimum shaft length for a trolling motor.
The Reason To Use A Long Shaft Trolling Motor
Long Shaft Trolling motors are appropriate in the following situations:
1️⃣ Long shaft trolling motors work with high freeboards.
2️⃣ Long shaft trolling motors work are useful on high seas.
Long Shaft Trolling Motors Work With High Freeboards
Boats with a high freeboard (height of a boat’s hull measured between the waterline and the boat’s deck).
A boat with a deep V hull (particularly one designed for offshore saltwater fishing) will have a higher freeboard than a dedicated inshore fishing boat (e.g., Bass Boat). This will apply, in particular, to the bow, which is higher off the water than at the stern.
Long Shaft Trolling Motors Are Useful In High Seas
Trolling motors used to be confined to inland water fishing boats.
They are becoming increasingly popular for use by open-water fishing craft owners. In these conditions, the boats have to contend with rough seas.
If the waves are higher and the boat moves up and down on the swell, a short shaft trolling motor will be forced out of the water more often. While this does not damage the motor, it causes noise which may scare the fish away and will be less effective in holding the boat’s position.
The Long Shaft Trolling Motors Has A Few Areas Of Weakness
Long Shaft Trolling Motors are subject to the following vulnerabilities.
- Long-shaft trolling motors experience more stress.
- Long-shaft trolling motors are more prone to damage.
- Long-shaft trolling motors are more difficult to store.
Long Shaft Trolling Motors Experience More Stress
The mathematician and philosopher Archimedes of Syracuse is quoted as saying,
‘Give me a lever long enough and a firm place on which to stand, and I will move the earth.’
The implication was that the longer the lever and the position of the fulcrum (pivot point), the greater the force which can be applied.
This is, unfortunately, the situation with long-shaft trolling motors. The “pivot point” is the mounting bracket on the boat’s bow or stern, and the “lever” is the shaft.
The longer the lever (shaft) and the further away the motor (at the end of the shaft) is from the mounting point, the more vulnerable it is to the forces applied. This can be exacerbated on high seas.
The higher a trolling motor’s thrust, the more pressure (torque) is applied to the shaft.
A trolling motor that produces high thrust will move the boat effectively at low speeds but will not necessarily be able to generate high speed.
Speed is determined by the horsepower generated by the trolling motor and the pitch of the propellor.
Long Shaft Trolling Motors Are More Prone To Damage
If the trolling motor shaft is too long, it runs the risk of being grounded, which may damage the propellor or even cause the Long Shaft to bend.
Longer Shaft Trolling Motors Are More Difficult To Store
While trolling motors generally can be stored on deck within their mounting bracket, the longer the shaft, the more deck space it uses.
📏 Can You Put A Longer Shaft On A Trolling Motor?
Many anglers have tried to extend the shaft length of the trolling motor; however, unless substantial reinforcing is applied, the DIY projects do not generally work.
This is because the materials and the attachment point to the shaft fail when excessive force is applied.
Manufacturers do not offer extension kits. However, if the shaft is too long, it is possible to cut it down into shorter lengths.
🤷♂️ How Long Should A Trolling Motor Shaft Be?
The shaft of a trolling motor should be long enough to ensure that the trolling motor’s propeller is submerged at twelve inches underwater. If the boat is used in rough waters, I recommend adding another five inches to this measurement.
The following table lists the recommended trolling motor shaft lengths.
|Trolling Motors Mounted On The Bow|
|Freeboard||Recommended Shaft Length|
|10 inches or less||36 inches|
|16 inches to 22 inches||42 inches to 45 inches|
|22 inches to 28 inches||48 inches to 52 inches|
|28 inches to 44 inches||54 inches to 72 inches|
|45 inches and more||87 inches|
|Trolling Motors Mounted On The Transom (Stern)|
|10 inches or less||30 inches|
|10 inches to 16 inches||36 inches to 42 inches|
|16 inches to 22 inches||42 inches to 48 inches|
|22 inches and more||48 inches to 52 inches|
🧪 How Deep Should Your Trolling Motor Be In The Water?
For calm inland waters, I recommend ensuring that the shaft length is long enough to submerge the propeller at least twelve inches below the waterline. This will reduce the chance of the propellor cavitating or churning the water.
Five inches should be added to the length if the boat is used in open seas or on choppier inland water surfaces. This means a minimum length under the water’s surface of seventeen inches.
If the system has a hand-mounted bow controller, a rule of thumb is to add another nine inches to the depth.
🗣 Final Words
Long shaft trolling motors are designed for use on boats with a high freeboard or when the vessel is regularly used on high seas with big waves.
Also, remember that bow mount motors and stern mounting areas could affect performance if you get the measuring wrong.
The correct shaft length must be chosen for the trolling motor because it will not work optimally if it is too long or too short.