Trolling Motor Buying Guide: Thrust, Voltage, Shaft Length and Mounting
Quick answer: Size thrust to your boat's loaded weight. A common rule of thumb is about 2 pounds of thrust per 100 pounds, with more for wind and current. That typically means 12V (30 to 55 lb) for small boats, 24V (70 to 90 lb) for most 16 to 20 foot bass and bay boats, and 36V (110+ lb) for bigger, heavier boats. Choose a shaft long enough to keep the motor about 12 inches underwater, a bow mount for serious fishing, and a saltwater-rated model if you fish salt.
A trolling motor lets you fish quietly, hold position on a spot, and move along a shoreline without starting the outboard. Modern motors add GPS anchoring that locks you on a waypoint, autopilot steering and built-in sonar. Buy the wrong size and you will fight the wind all day or drain your batteries by noon. This guide covers thrust, voltage, shaft length, mounting, freshwater versus saltwater, and power.
Step 1: Choose thrust and voltage
| Typical boat | Thrust | System voltage | Batteries |
|---|---|---|---|
| Kayaks, jon boats, small skiffs | 30 to 55 lb | 12V | 1 |
| 16 to 20 foot bass, bay and flats boats | 70 to 90 lb | 24V | 2 |
| Larger and heavier boats, rough water | 110 lb and up | 36V | 3 |
Each 12 volts needs one 12V battery wired in series, or a single lithium battery built for the higher voltage. Higher voltage motors draw less current for the same thrust, which means longer runtime and cooler running. When in doubt, size up, especially if you fish wind-exposed flats, big lakes or current.
Step 2: Get the shaft length right
The motor head should sit about 12 inches below the surface so the prop stays in the water when the bow rises and falls. Measure from where the motor mounts to the waterline, then use the manufacturer's chart.
| Bow height above water | Typical bow-mount shaft |
|---|---|
| Up to about 10 inches | 36 inch |
| About 16 to 22 inches | 42 to 45 inch |
| About 22 to 28 inches | 48 to 52 inch |
| About 28 to 34 inches | 54 to 60 inch |
Add several inches if you fish rough water, and more for hand-control bow motors you operate standing at the bow. A shaft that is too short lets the prop cavitate and break the surface. One that is too long can drag in shallow water.
Step 3: Pick a mount
- Bow mount: pulls the boat from the front for precise control. The standard for serious fishing. Steered by foot pedal, hand tiller or wireless remote.
- Transom mount: clamps to the stern, simple and affordable for small boats and jon boats.
- Engine mount: attaches to the outboard's cavitation plate on some boats.
Step 4: Freshwater or saltwater?
Saltwater models have sealed electronics, corrosion-resistant hardware and sacrificial anodes. Using a freshwater motor in salt or brackish water will shorten its life dramatically and may void the warranty. In Florida, if you ever fish the coast, buy saltwater.
Step 5: Features worth paying for
- GPS anchoring: holds you on a spot automatically, often called spot-lock or anchor mode. The biggest upgrade in modern fishing.
- Autopilot and route following: steers a heading or follows a shoreline contour.
- Integrated sonar: a transducer built into the motor head feeds your fishfinder.
- Brushless motors: quieter and more efficient on many newer models.
- Wireless remote and foot pedal options: control from anywhere on the boat.
Step 6: Power it properly
- Use deep cycle or lithium batteries sized for how long you fish. See our marine battery guide.
- Run heavy enough cable for the distance from the batteries to the bow.
- Install the circuit breaker the motor manufacturer specifies, close to the batteries.
- Add a plug and receptacle so you can remove the motor or disconnect power easily.
- Recharge after every trip with a multi-bank onboard charger. See our battery charger guide.
Our picks
In stock at Boat Supplies Direct.
Premium freshwater bow mount
Garmin Force Freshwater Trolling Motor, 57 inch. A quiet brushless motor with GPS anchor lock that integrates with Garmin chartplotters. Freshwater use only. Add the Force Foot Pedal or a spare Force Remote.
Wiring and power
Marinco 24V Trolling Motor Wiring Kit with 70A plug and receptacle or the 36V kit.
Sonar on the trolling motor
Garmin GT52HW-TM Trolling Motor Transducer with CHIRP, down and side imaging, or the LiveScope LVS12 shaft mount.
MotorGuide owners
MotorGuide PinPoint GPS Navigation System to add GPS anchoring, and the Xi Series Wireless Remote FOB.
Frequently Asked Questions
How much thrust do I need for a trolling motor?
A common rule of thumb is about 2 pounds of thrust per 100 pounds of fully loaded boat weight, with extra for wind and current. Most 16 to 20 foot boats use 70 to 90 lb motors.
What shaft length trolling motor do I need?
Measure from the mount to the waterline and use the manufacturer's chart so the motor head sits about 12 inches underwater. Add length for rough water.
12V, 24V or 36V trolling motor?
12V suits small boats with motors up to about 55 lb of thrust. 24V covers most 70 to 90 lb motors, and 36V powers 110 lb and larger. Higher voltage means less current draw and longer runtime.
Can I use a freshwater trolling motor in saltwater?
No. Freshwater motors lack sealed electronics and corrosion protection and will degrade quickly in salt or brackish water. Buy a saltwater-rated model for coastal use.
What is spot-lock on a trolling motor?
A GPS anchoring feature that automatically holds the boat on a chosen spot by steering and adjusting thrust against wind and current.
Do I need a circuit breaker for a trolling motor?
Yes. Install the breaker size the motor manufacturer specifies, close to the batteries, to protect the wiring.
This guide is general information. Always follow your trolling motor manufacturer's sizing charts and wiring instructions.
