How to convert thrust to horsepower? How many #’s of thrust equals out to 1 hp?
Actually, is there a relationship between hp and thrust? Can thrust be converted to horsepower?
The short answer is YES, but the lb thrust to horsepower conversion is a little tricky.
Today we are gonna work out how to translate pounds thrust to horsepower in the easy way!
And more than that, you’ll learn everything you care about thrust to hp as a boat owner.
Content:
- Thrust vs Horsepower: What’s the Difference
- Thrust to Horsepower Convertor: 2 Methods
- Pounds of Thrust to Horsepower Chart
- More Thoughts About Thrust vs HP
Thrust vs Horsepower: What’s the Relationship
By landing on this page, you should have already noticed that the trolling motors are rated in pounds of thrust. Whereas the regular outboards (electric or gas) are in horsepower.
So thrust vs horsepower, what’s the difference?
In fact, the thrust and horsepower measures totally different things:
The pounds of thrust is a static force measurement.
It is a result of the power developed by the electric motor, the propeller shape, pitch and dimensions, and the speed in revolution per minute.
Horsepower is a measurement of “work” being performed.
To be more exact, one horsepower is a unit of measurement equal to 550-foot pounds of “work” per second. It means a horse could lift a 550-pound weight one foot in one second.
So it’s hard to say how much horsepower is a pound of thrust, since there is no precise correlation between thrust and horsepower.
All we can do is to get an estimated figure of lb thrust to horsepower. And here is how.
Thrust to Horsepower Converter: Two Methods
Does anyone know how to correlate the ratings of a Minn Kota electric trolling motor to HP?
To convert thrust to horsepower, there are generally two methods
Method 1: The Easy Way to Compare Thrust to Horsepower
Experiments determined one horsepower equals 746 watts of energy. So first, you got the horsepower to watts:
1 HP = 764 Watts
And in theory, you can fondly get a rough idea of the horsepower of an electric motor by taking its rated current draw (amperes) and multiply it by the voltage. That is:
Power (watts) = Current Draw (amps) x Voltage
So here you get a rough thrust to horsepower equation:
Horsepower (hp) = current draw (amps) x voltage/764
Then you should make a guess as to the efficiency of the motor and there are always other power factors to affect the conversion rate.
So the adjusted thrust horsepower formula goes as follows:
Horsepower (hp) = current draw (amps) x voltage x efficiency x power factor/764
Assume 85% efficiency for the electric motor and 0.9 power factor (typical value).
Let’s take the 74 lbs of thrust trolling motor from Minn Kota as an example. It has a max amp draw of 45 amps at 24 volts. Here is how to compare pounds of thrust to horsepower:
45 x 24 x 0.85 x 0.9/746 = 1.11 hp
So 75 pounds of thrust of a trolling motor roughly equals to 1.11 horsepower.
Method 2: Accurate Way to Calculate Pounds of Thrust to HP
If you are serious about finding an accurate number of the horsepower to thrust, you should be prepared for some learning curves and do the math.
In fact, the amount of thrust delivered by a propeller at a given horsepower is decided by a lot of variables including:
- blade shape (mostly aspect ratio and sweep)
- the number of blades
- the advance coefficient J (J=Va/Dn where D=the propeller diameter, n=rps,Va= velocity of advance in fps)
You can learn more about the thrust to horsepower calculator with John on this thread.
Pounds of Thrust to Horsepower Chart
I have a 55 lb. thrust trolling motor, would that be equal to any horsepower?
What’s the equivalent of a 30 thrust trolling motor in HP?
To help you quickly find the result, here is a chart that compares pound of thrust to hp.
The estimated thrust to horsepower is based on the method #1 of lbs to hp calculator with 85% motor/system efficiency and 0.9 power factor.
And here we mainly discuss the pounds to thrust on the boating field with a relatively limited thrust range commonly seen as below and not the jet engine field.
| Pounds of Thrust (lbs) | Amps | Voltage | Horsepower | Product for Your Reference |
| 30 | 30 | 12 | 0.36 | Minn Kota Endura C2 |
| 40/45 | 42 | 12 | 0.5 | Newport Vessels NV-Series (46 lb) |
| 50/55 | 50 | 12 | 0.6 | Newport Vessels NV-Series (55 lb) |
| 70 | 42 | 24 | 1.01 | Minn Kota Maxxum (70 lb) |
| 80 | 56 | 24 | 1.35 | AQUOS Haswing CaymanB (80 lb) |
| 101 | 46 | 36 | 1.66 | MinnKota Riptide (101 lb) |
| 112 | 52 | 36 | 1.87 | AQUOS Haswing (110 lb) |
So 1 hp trolling motor basically equals to 70 lbs of thrust, and about 0.6 horsepower is a 55 lb thrust trolling.
More Thoughts About Horsepower vs Thrust
Here are some common confusions or misunderstandings of the lb thrust to horsepower. Check them out to help you make a wise choice.
#1. Trolling Motor (Thrust) vs Outboard (Horsepower)
Searching for thrust to hp in order to get a proper electric replacement for your gas outboard, right?
Be minded that all the electric trolling motors measured by pounds of thrust (lbs) are much less powerful than the regular outboard, usually with less than 2 horsepower.
So if you are calculating the thrust to power for speed/power and the ability to run all day, you should go straight with the regular outboard. Check out our comprehensive guide here: Trolling Motor vs Outboard.
#2. More Thrust or Horsepower Not Always Equals to Faster Speed
Notice that there are differences in prop design that decides the max speed of your boat.
So when you increase engine horsepower or thrust, you may need a different prop to take advantage of it if the previous horsepower (thrust) reaches its top speed.
That means you won’t get any more out of a trolling motor than the prop design allows. A 100# motor might not push a boat any better than a 48# if both use the same prop.
If you’re looking for more speed from a trolling motor, you should look for a different prop.