Long Shaft Trolling Motors [Explained]

ByMathew F Updated On:

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.

If it’s too long, it could be damaged on a submerged reef and be more prone to bending caused by the forces it is subject to.

Selecting 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.

🎓 Here’s a quick guide:

Bow-Mount Motors: Measure from the mounting surface to the waterline. Add 5″ for fishing in rough water or 9″ for bow-mount hand control motors.

Transom-Mount Motors: Most boats have similar transom to waterline distances. Standard shaft lengths usually suffice.

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.

Advantages of Long Shaft Trolling Motors

Long Shaft Trolling motors are appropriate when the boat has a high freeboard and when the fishing is taking place in rougher conditions.

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.

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.

Drawbacks of Long Shaft Trolling Motors

Long Shaft Trolling Motors are subject to the following vulnerabilities.

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 that 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.

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.

While trolling motors generally can be stored on deck within their mounting bracket, the longer the shaft, the more deck space it uses.

Optimal Trolling Motor Shaft Length

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 tables below list the recommended trolling motor shaft lengths.

Trolling Motors Mounted On The Bow
FreeboardRecommended Shaft Length
10 inches or less36 inches
16 inches to 22 inches42 inches to 45 inches
22 inches to 28 inches48 inches to 52 inches
28 inches to 44 inches54 inches to 72 inches
45 inches and more87 inches
  
Trolling Motors Mounted On The Transom (Stern)
10 inches or less30 inches
10 inches to 16 inches36 inches to 42 inches
16 inches to 22 inches42 inches to 48 inches
22 inches and more48 inches to 52 inches

Closing Remarks

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.

Frequently Asked

Ensure that the shaft length is long enough to submerge the propeller at least twelve (12) 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.

For a 16-foot boat, generally, a trolling motor with 55 to 70 pounds of thrust is recommended. The motor should be 42 to 52 inches in shaft length, but this can vary based on the boat’s weight and usage.

Written by:

Mathew F

I’m the founder and chief editor here at Kite Ship. The electrification of boating is the most exciting thing to happen to the marine industry in a generation! Welcome, and I hope that we can provide the portal you need to dive into the world of electric propulsion and power.