So you want to buy a trolling motor? That’s great.
But how do you know what trolling motor is suitable for your boat?
And what size of trolling motor do you need?
Trolling motors differ in size and style. And to determine what size of trolling motor to buy, there are factors you need to take into consideration.
But first, you need to figure out what type of trolling motor is suitable for your boat before you get to the size.
There are two types of trolling motors: bow mount motors and transom mount motors.
And trolling motors come in three configurations: 12volts, 24 volts, and 36 volts. Knowing what type to buy depends on how big or small your boat is.
Bow mount motors are ideal for large and medium-sized boats like bass and bay boats. And transom mount motors are best for small boats like canoes and kayaks.
How to tell what size of trolling motor to buy for your boat
There are several factors that can help you determine just what size of trolling motor to buy for your boat. And they are as follows:
Thrust
One of the key considerations when deciding on the size of the trolling motor to buy is thrust. You need to calculate how much thrust your boat needs.
Trolling motors are rated in pounds per thrust. And the general rule is, for every 100lbs of the weight of a fully-loaded boat, you need a minimum of 2lbs of thrust.
So to know just how much thrust your boat needs, take the weight of your boat, and divide it by 100 and then multiply by 2.
So for instance, if the total weight of your boat, this including all the stuff on it is 5000 pounds. The thrust your boat requires is (5000/100 )*2=100lbs.
Bear in mind that the larger the boat, the more thrust it needs. And when your boat has adequate thrust, it is steady and you can cruise at 4mph easily.
Voltage
Trolling motors are available in three different voltages: 12v, 24, and 36v. When a battery has a high voltage it means it has high power output. So a 36v trolling system produces more power than a 12v system but its also bigger in size.
36v trolling motors use three deep cycle batteries, 24v uses two batteries, and 12v uses one battery.
So depending on the dimensions of your boat in terms of size and weight, you can determine whether you need a 12v, 24v, or 36v.
Each of them provides different pounds of thrust:
- 12 volts provides 55 pounds
- 24 volts provides 80 pounds
- 36 volts provides 115 pounds
So if you need your boat to have more thrust, all you need to do is add the number of batteries.
Shaft Length
Shaft length is of key importance because choosing the incorrect length can cause your trolling motor to cavitate and lose thrust.
To get the correct length, if you have a transom trolling motor, the general rule is that the top part of the motor should be submerged 12 inches in the water.
If you have a bow trolling motor, you need to measure the length between your boat’s gunnel and the waterline then add an extra 20 inches.
So here are the recommended transom and bow motor shaft lengths:
| Distance Between Transom and Waterline | Shaft Length |
| 0 to 10 inches | 30 inches |
| 10 to 16 inches | 36 inches |
| 16 to 20 inches | 42 inches |
| Distance Between Bow and Waterline | Shaft Length |
| 0 to 10 inches | 36 inches |
| 10 to 16 inches | 42 inches |
| 16 to 22 inches | 42 to 45 inches |
| 22 to 28 inches | 48 to 52 inches |
| 28 to 34 inches | 54 to 62 inches |
| 34 to 44 inches | 72 inches |
Propeller
Not many anglers consider the style and design of a propeller when it comes to the size of the trolling motor. But propellers play an important role in moving a boat and to some extent are important when it comes to choosing a trolling motor.
Propellers come with either 2 blades or 3 blades. A 2-blade has less thrust but it also doesn’t wear out the trolling motor’s battery. A 3-blade has more thrust but it also uses more battery charge.
Two blade propellers are usually found in transom motors while 3-blade propellers are found in bow motors. So if you prioritize thrust when choosing what size of trolling motor to buy, consider the propeller as well.
Conclusion
Getting the right size for your boat depends on the size of your boat. If you have a canoe or kayak, a 12v trolling motor is adequate to move your boat with ease and speed.
If you have a bass boat or other large boat, a 24v or 36v motor system is what you need.
Cost is also a consideration. Large motor systems are more expensive than small ones. But don’t focus too much on the cost. You would rather spend more and get a motor that is suitable for your boat and your needs.
