T-Pain Is On A Boat: Re: [Electric Boats] Re: Sailboat Trolling Motor Options

Monday, August 23, 2010

Re: [Electric Boats] Re: Sailboat Trolling Motor Options

Gentlemen:

This is why 746 watts is precisely one horsepower. It is completely independent of the efficiency of either type of engine. It is a measure of the output power of the engine, usually but not always measured at the shaft. The little subscript "f" is just to indicate that the measurement is made at the surface of our planet so that we can treat weight in pounds as a measure of mass.

1 HP≡ 33,000 ft·lb_f/minby definition= 550 ft·lb_f/ssince1 min = 60 s= 550×0.3048×0.45359237 m·kg_f/s since1 ft= 0.3048 m and= 76.0402249068 kg_f·m/s1 lb= 0.45359237 kg= 76.0402249068×9.80665 kg·m²/s³g= 9.80665 m/s²= 745.69987158227022 Wsince1 W≡ 1 J/s = 1 N·m/s = 1 (kg·m/s²)·(m/s)

1 hp = 550 ft·lb_f/s, 1 ft = 0.3048 m, 1 lb_f ≈ 4.448 N, 1 J = 1 N·m, 1 W = 1 J/s: 1 hp = 746 W

All courtesy of Wikipedia.

Happy Sailing,

Ned

On Aug 23, 2010, at 11:19 AM, sirdarnell wrote:

I'm sorry, but that statement is meaningless. ICE engines are not rated based on the gallons or liters per hour they burn (watts or energy input), but on the amount of work they do in horsepower or kilowatts (watts or energy output.) So they are already rated in energy output, which is the conversion I did. Remember 550 pounds-feet per second is 1 horsepower, i.e. work done.

Watts, in terms of watts used to run an electrical motor is just how much fuel is needed to run a motor, electrical fuel and not chemical fuel, but still fuel burned and not work produced. We want to know how hard or fast a motor or engine can push our boats to find out if performance will be enough for our needs. After we have the performance needed we can look at fuel burn rates (Watts or Gallons per hour) and how much storage is needed (Batteries or tank size) for the range we want. Assuming we can get the performance and range in a realistic package. A 50% efficient motor "burning" 746 watts is still only 5/8ths as powerful as an 80% efficient motor "burning" (drawing is the proper term) 746 watts. Internal combustion engines are so inefficient that they are rated on output power, just to avoid the embarrassment.

--- In electricboats@yahoogroups.com, "Ron" <rlgravel@...> wrote:
>
> Be sure to do the same input calculation for the ICE that you did for the electric motor.
> Cheers
> Ron