Trolling Motors are Measured in Terms of Thrust
Gliding silently along the waterways and hooking a big one is pretty much the way every keen fisherman likes to spend their morning. Your good ol’ faithful electric trolling motor is the one that makes this happen by keeping noise to a minimum.
- Trolling motor thrust over horsepower
- Factors that affect thrust
- Clear up a couple of misconceptions and old wife’s tales
A general guide for the size trolling motor you can consider can be gained by thinking about the type of fishing you do.
1. What is Trolling Motor Thrust?
Just as an outboard’s power is measured in horsepower*, a trolling motor is rated in terms of thrust.
Thrust is measured in pounds (lbs) and is the amount of power that is needed to propel, or push, your boat through the water obtaining a good trolling speed, having optimal maneuverability, endurance and getting the most out of your time on the water.
- higher voltage = higher thrust
Trolling motor models are available in a choice of voltages, 12v, 24v, 36v. As a guide 12v/55lbs, 24v/80lbs
The more powerful options offer more than 100lbs of power, strong enough to suit larger, heavier boats.
so we’ll also discuss the conditions that will affect your choice
The amount of thrust you need and when you might need to step it up a level.
Think in terms of endurance.
As a guide we’ll make the assumption that you’ve a boat 16 ft or over
- If you go out fishing for a few hours at a time, and very occasionally a 12 volt system should be adequate.
- A better choice would be a trolling motor with at least 24volts, particularly if you’re hitting the water more often.
- Several times a week, ideally a 36 volt system would be the best option.
*(In contrast to horsepower which is the amount of power produced by the engine in order for it to function effectively for the work it does. The force you feel when you accelerated is referred to as torque.)
2. What affects trolling motor thrust?
Not enough battery power. If you’ve got a big boat and a small motor and battery, well it’s common sense that you won’t be winning any races. You’ll also shorten the life of your motor as it works overtime to push what feels like an aircraft carrier through the water when it’s designed for a canoe.
The basic rule of thrust:
‘For every 200lbs of your vessels gross weight, you’ll need 5 lbs of thrust.’
Now, remember this is total gross weight. This means it includes your boat, your mates, all of your combined gear, the esky and the dog. If you usually go out with one mate most weekends, then decide to have a fishing trip with two others tagging along, then you may want to step it up a level and rig up an extra battery so it doesn’t put too much stress on your motor and shortening the lifespan.
Calculation example based on weight of the boat being 1,500lbs and the boat’s maximum capacity of 1,200lbs
(1,500lbs + 1,200lbs = 2,700lbs. 2700 /200 = 13.5 x 5lbs of thrust = 67.5lbs)
Note: If you buy a trolling motor that is underpowered it will be sluggish and won’t effectively hold your boat in position. Beware, this is a major frustration.
If you like to fish out on a big dam, lake or lagoon, then you won’t be encountering current. The same if you usually potter around quiet estuaries and shallower waters then you’ll get away with the lowest level of thrust on your motor.
So if you decide to try out a new spot with currents, waves or faster moving water, then step it up a level, switch to a higher speed or perhaps think of even stepping up to a bigger motor.
Tip: Always take a spare battery (or two) when trying out new fishing spots so you don’t get stuck or have your motor become sluggish due to harsher conditions.
3. Run Time
Calculate your motor’s run time with the batteries you have. If it’s a boy’s weekend fishing for 3 days then you may want to step up a size to a more powerful motor with one larger battery rather than having to take along 3 additional batteries to make sure it lasts the time you’ll be away.
Stronger winds and waves increase the strain on your motor and influence the power you’ll need.
If you fish in these conditions it’s good to have a shallow water anchor to help you stay put without draining your battery life by using additional thrust to keep you there.
5. Wrong Motor Size
The larger and heavier your boat, the stronger the thrust you need to propel it through the water.
Here’s a quick reference guide to help you out. As you can see, the boat length (longer boat = more weight) is a quick rule of thumb way to get an idea of the amount of thrust needed.
What happens if your motor is too small?
- you’ll have trouble positioning your boat
- the response time will be down
- your boat will be very sluggish
- you’ll burn the motor out quicker
- the life span of the motor will be substantially reduced
4. Misconceptions and Old Wives Tales
1. More batteries = more power
A common misconception is that if you add more batteries, then your motor will go faster. That’s not true. Trolling motors have a top speed so you can add 15 batteries if you like, your motor will run like a dream but it won’t go any faster. And chances are you’ll do yourself a mischief tripping over one of the blasted things.
2. Bigger is better
If you’re fishing from a kayak, then you don’t need the biggest motor on the market thinking you’ll turn it into a speedboat and go faster. Thrust is for propelling a boat through the water, so if you have a Jon boat or a kayak and you rig it with the biggest motor there is, sure it does the job, but so will one a third of its thrust power so you’re wasting your money and probably looking a little silly in the process.
3. Motor speed increases with thrust size
Increasing thrust doesn’t increase the top speed of the motor. This is where trolling motors, (or electric motors) are different from gas motors.
Top speed of a trolling motor is around 5 mph.
So to answer common queries about speed: ’55lb thrust trolling motor speed?’ or ’30lb thrust trolling motor speed?’ The answer will be around 5 mph provided you’ve chosen the size big enough for your boat.
Trolling motor speed is affected by prop pitch and motor RPM, revolutions per minute. (The number of rotations around a fixed axis). RPM’s are limited by the number of volts applied to the speed coil and you can calculate a maximum speed if you know the RPM of the motor. The formula page on this link from Minn Kota sets it out clearly.
The pounds of thrust (force) the motor exerts can be different (eg 55lbs or 80lbs, 115lbs etc) but if they have equal RPM’s the maximum speed will be exactly the same.
The simple fact is, normal outboards are loud, churn up the water and yes, they’re great for getting you to your favorite spot in a hurry, but once you’re there, a trolling motor’s tranquil troll in virtual silence quadruples your chances of landing what you’re chasing.
NADA directory – if you’re unsure of the weight of your boat for calculation purposes, this directory has some valuable information.