How do you convert horsepower into m.p.h.?

Question

example; if you bought a 9.9 hp boat motor,how many m.p.h. could you expect to go?

Answer 1

Horsepower is a measure of an engine's ability to do work, specifically, the ability to move a given amount of weight a given distance in a given time. One horsepower can move 33,000 pounds one foot in one minute.

That said, what you have to move affects speed. In your case, it is a boat, so a couple of factors will affect the speed you can achieve. One is hull design, specifically, how much draft the boat has, and how streamlined is the hull. A square barge, for example, will have more bow friction with the water, and since you have to push water out of the way to move, the amount of water you push adds load to the engine. Likewise, a hull that sits low in the water requires more horsepower to push as well, as compared to say, a hydrofoil, which rides on planes on top of the water, reducing friction.

If you are talking about something like a Jonboat, with one person in it, and no other cargo than fuel, I would guess your 9.9 horsepower engine might manage about 15 miles per hour, maybe even 20 mph if you are not terribly heavy.

Answer 2

Horsepower To Mph

Answer 3

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RE:
How do you convert horsepower into m.p.h.?
example; if you bought a 9.9 hp boat motor,how many m.p.h. could you expect to go?

Answer 4

You can't

Horsepower is only an indication of power of the motor, and many other factors including the shape of the vehicle, the weight of the vehicle determine how fast a vehicle can travel.

horsepower is only one factor of many in determining speed of a vehicle.

Even a compairson of maximum horsepower (I'm assuming the number you're looking at) is not a good indication of how fast a boat will go. Given the same exact boat, with engines with different "maximum" horsepower, the engine with the maximum horse power may not necessarily accelerate the boat faster. Horsepower for an engine is actually a curve, and not a single number.

Answer 5

You cant convert these two figures. It depends on the weight of the vehicle, size of tires, transmission gearing, rear end gearing, etc

You could have two identical vehicles with the same hp but one has 3:11 gears and the other has 4:10 gears, the 3:11 gears could essentially reach a higher top speed before the rpms run out.

In the boat world, it really depends on the weight of the boat, the aero dynamics, water conditions, wind, etc. A pontoon boat with a 200 hp engine will not go as fast as a speed boat with a 200hp engine due to the coefficient of drag.

Answer 6

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While the others are strictly correct there is an approximate conversion. When Frank Whittle was trying to get the RAF to pay attention his engine was producing about 1,000 pounds of thrust. The thing that got the RAF to pay attention was that that's about what a Rolls Royce Merlin was producing in a Spitfire at the time. So we can say that under limited circumstances it's about 1:1. Does this bear any sort of examination? One of the difficulties is that when gas turbine cores are put to other uses they are often run at more or less conservative power levels. A Rolls Royce Olympus engine produced about 19,000 pounds of thrust in aircraft uses and 25,000hp in marine uses. So 1 to 1... sometimes... roughly.

Answer 7

As a general rule you have to know the conditions you will be working in.

A car engine can have its mile per hour-age totaled by multiplying the number of horsepower by two and then dividing by half of the number of cylinders. So a 600hp V6 would be capable of going 400 miles per hour. This only works with Russian cars.

For boats it is an entirely different story. This is no easy task, but it can be done. First you have to look at the website or information provided by the motor manufacturer. I will use Briggs and Straton for my example. A 9.9hp Briggs and Straton motor has a top fluid flux leakage rate of 1.6 ml/hour. You have to take the square of the fluid leakage rate and compare it to the hp. For any motor where fluid flux leakage (ffl) is less than hp you square the horsepower and divide by (hp/ffl). Once this number has been obtained you have to add the square root of the weight of the boat in pounds. Now you have the approximate top speed of what your boat will be.

If they ffl is greater than the hp of the engine then you really should just consider getting another engine.

Answer 8

Above are good answers.
I guess you can use a different pitch propeller. May change the Fuel Jets in the carburetor to gain a little extra horse power.

The link is Caravelle Boats, but, if you read it, you can learn a little about propellers.

Answer 9

there is no set equation it depends on conditions baot size and weight with a 9.9 hp motor not very fast.. maybe 10 or 12 mph.

Answer 10

9.9 on a 12 foot boat is differnt on a 20 foot boat...you cant do it