If you’re looking at buying a trolling motor, then you have probably looked into motor size. After all, you want one that is big enough to move your boat and help you achieve your goals, but you don’t want to spend too much on one that is too big for your boat.
There are actually a few factors to consider when choosing the size of your trolling motor. Examine them according to the standards below, then buy the best-size trolling motor for your boat.
Table of Contents
- What Does My Trolling Motor Need to Do?
- Trolling Motor Thrust vs. Boat Weight
- Get Plenty of Voltage!
- Consider Shaft Length
- Motor Use and Trolling Style
What Does My Trolling Motor Need to Do?
Before you choose a trolling motor, you should make sure you know what you need your trolling motor to do for you. Most people just want to be able to cruise slowly across a lake while fishing.
However, your trolling motor should also:
- Help your boat get on plane, or skim through the water with the bow lifted. This helps it move through the water with ease.
- If you use GPS on your trolling motor, it should be able to lock onto a place and keep you there without struggling.
- Allow you to steer straight, without getting bumped or blown off course.
- Respond easily when you use the motor to steer. It should allow you to go where you need to go without a hassle.
To do all of these things, you will need a trolling motor that is the right size for your boat, in more ways than one. Keep reading to find out the different size factors that can affect trolling motor choice.
Trolling Motor Thrust vs. Boat Weight
The most important factor when it comes to getting the right-size trolling motor for your boat is thrust. Thrust is measured in pounds and is the standard way of talking about how powerful the motor is.
Note that a motor with more thrust will not necessarily go faster. In fact, most trolling motors are designed to only go about 5 miles per hour, no matter how much thrust they have. Instead, motors with more thrust have the capacity to move larger, heavier vessels through the water.
In general, you will want 2 pounds of thrust for every 100 pounds that the motor will be moving through the water. This includes the weight of the boat itself, as well as the weight of any people and gear that it is carrying.
Other experts recommend a little more thrust – 5 pounds for every 200 pounds of weight that will be moving across the water. If you are on the cusp, choosing between two motors, make sure you calculate your needs using both of these figures.
That way, you can decide whether you want a little more or a little less thrust than the recommended amount. Most people recommend going with a little more, as long as it’s not a lot more thrust than you will need.
If you don’t know how much your boat weighs, your local marina might have a scale. You can also check with the manufacturer or talk to a boat mechanic to get an estimate.
While you can look up estimations for the weight of a boat based on its length, these aren’t always accurate. If your boat was made of different materials than the ones used in the estimate, the numbers you see won’t necessarily apply to your situation.
If you fish in places where there is often high wind or you have to fight a strong current, you’ll want more thrust. This allows your boat to maintain position or move against the weather and current no matter how strong it gets.
Get Plenty of Voltage!
The higher the voltage rating on your trolling motor, the more thrust you will get. Trolling motors come in 12V, 12/24V, 24V and 36V versions. The most thrust you can get out of a 12V motor is 55 pounds, while a 24 V motor can give you up to 80 pounds.
The maximum thrust that you can get from a trolling motor is around 100 pounds, though a few advertise slightly more than that. These are for the largest types of boats out there that use trolling motors, like pontoon boats.
When it comes to choosing a trolling motor, you need to get one with enough thrust but you also need to make sure that you have enough space on board your boat for the batteries. You will need one battery for every 12 volts that your trolling motor needs.
Thus, a 12 volt motor needs 1 battery, a 24 volt motor will need 2 batteries, and a 36 volt motor will need 3 batteries. When considering what size trolling motor you need, make sure you have space in your boat for all of these batteries, too!
Consider Shaft Length
The length of the shaft on the trolling motor is another factor you should consider when buying a trolling motor for your boat. The best one will have the proper shaft length for your needs.
You want your trolling motor shaft to be long enough that the propeller is fully submerged in the water at all times. Otherwise, it cannot move your boat forward efficiently and you will waste a lot of power or overwork your trolling motor.
If you will use your boat in choppy water or water with waves, you will want the shaft long enough that the propeller is always under the water. Your boat may pitch and roll and you want your propeller at least 6” under the water at all times.
Similarly, if you will be using your boat in very shallow water, you need to find a balance between a shaft that is long enough but does not hit the ground. If you cannot find one that will work, you will either need to paddle in shallow water or risk getting stuck or damaging your trolling motor.
The standard shaft length on a trolling motor is 42 inches. You will need to check and see if this will work for you.
Start by measuring the distance between where the trolling motor will sit on the boat or the transom to the water line. If you are considering a MotorGuide trolling motor, add 16 inches to that. If you are considering a trolling motor from Minn Kota, add 20” to it.
The number you get is the minimum shaft length that will work for you with that brand of motor. If you’re looking at another brand of motor, consult a specialist to find out how much length to add to your original measurement.
Motor Use and Trolling Style
Different people use their trolling motors differently. Some anglers like to troll back and forth across an area, staying in nearly constant motion.
Others use their trolling motors to lock on to a particular spot and keep them there. While these are both valid ways to use a trolling motor, you may want to buy a trolling motor specific to your needs.
If you want a motor that you plan to run all day, make sure you get one that is designed for these purposes, rather than one made to be turned on and off. If you want to lock in a location, make sure you get a trolling motor that has GPS functionality.
Note that trolling motors with more features may be bulkier and take up more space. Take this into consideration before you buy your new trolling motor.
What Size Trolling Motor Do I Need for a Certain Size Boat?
Most of the questions we get about trolling motors take the form, “What size trolling motor do I need for a 14 ft. boat?” or “How big of a trolling motor does a 20 ft. boat need?”
We can only make suggestions based on the length of your boat (most 14 ft. boats need less than 55 lbs. of thrust and most 20 ft. boats need 90-100 lbs. of thrust, for instance). To give a more specific answer, we need to know about weight.
The material your boat is made of, how many people you usually have on board, and how much gear you bring with you. Once we know the answers to those questions, we can give you a better recommendation on how much thrust your trolling motor needs.
How Fast Will a Trolling Motor with 80 lbs. of Thrust Go?
All trolling motors will go 3-5 miles per hour. They are not designed to move a boat faster than this, no matter how much thrust they have.
Remember, thrust is a measurement of how much weight the motor can move, not how fast it will go.
Can I Use Any Trolling Motor on an Inflatable Boat?
As long as you have a place to mount your trolling motor, you can use any trolling motor you want on your inflatable boat. You will need a sturdy transom or another solid place where you can mount the motor.
Keep in mind that there are a few trolling motors designed specifically for use with inflatables. However, most of them are more generic than that and can be used anywhere.
There are many good brands of trolling motors out there and they all come in multiple sizes. This includes different amounts of thrust, and different shaft length.
You also need to take into account the size of the motor and its features compared to the size of your boat. Consider, too, the amount of space that the batteries your trolling motor needs will take up on your boat.
Once you’ve considered all of these things, choose the trolling motor that best fits all of your needs. Then don’t waste any more time getting out on the water!