Re: Thrust vs Horepower
Posted by GES on 2006-07-14 11:53:04
in reply to Thrust vs Horepower posted by Ralph on 2006-07-06 02:30:26
It's a little difficult to compare, as it is not easy to find out how each was measured.
I have always assumed that electric motor thrusts are measured with a clamped motor; not going anywhere. Under those conditions the water flow and the propellor efficiency (and slip) are quite different from when the boat is moving along and you have a less turbulent water flow around the propellor.
But as others have said one HP is 746 Watts, so a 4 HP electric would consume about 3 KW if it were 100% efficient, which is 250 Amps at 12 Volts.
Safe to say Ralph that you don't want to carry any 250 Amp battery around in your 10 footer. That Minn-Kota E-drive I think they call it; is 48 Volts so it would be around 63 Amps; if it was 4 HP (think it's two)and I'm sure you don't want four 12 Volt batteries in your pram with you. Turns out I was looking at that e-drive just yesterday, at a Bass Por-shop near Atlanta, and you don't want one of those on your pram. As someone said, the motor is HUGE!! five or six inches in diameter, and longer than your 55# electric.
Ralph if you can stand the sound of the four stroke, and the motor weight, I think you are way ahead with that. I suspect a gallon of gas and you are good for all day.
The Thrust-HP connection is not the real issue; the plain fact of the matter is that you can't compare the energy per pound of gasoline with that of lead acid batteries, which are not even A very high energy density battery chemistry.
Take the gas Ralph if you think the noise is within your tolerance.
Electric motor propellors have never impressed me with efficiency either; they are much too flexible.
Let us know how it works out.
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