Re: [PSUBS-MAILIST] Horsepower

[Kenneth Schulze <aquamari@cruzers.com>]

Hi Doug,
I think much of the confusion comes about because internal combustion engines are
rated differently than electric motors.  Most gas/diesle engines are rated at
their peak horsepower output, but are operated at 50 to 70 percent peak rpm.
Electric motors are rated for continuous operation, but can be pushed to 200% for
a limited time due to heat build up and possible overheating.
Another "apples to oranges" comparison is made by not including the energy
storage system, such at fuel storage volume and weight.  Batteries can only
depleted to 30 or 40% of full capacity, any more will shorten the life of the
battery system.
Therefore, be careful how you compare internal combustion engines with electric
motors.
Take care,
Ken Schulze

SeaLordOne@aol.com wrote:

> Teammates,
>
> Please help me with this one.  According to an article in BOAT/U.S. Magazine
> (January 2000, pages 24-25), electric motors somehow provide three times the
> performance of internal combustion engines.  How can this be?  Horsepower is
> horsepower is horsepower, isn't it?
>
> The article (Electric Boats Charging Back) is about coverting gasoline or
> diesel boats into electric ones.  The author (Ryck Lydecker) says: "He
> calculates that to replace internal combustion engines, particularly in
> sailboats, the power ratio is about three-to-one.  That is, a 3-hp electric
> motor is adequate to replace a 9-hp outboard."  I thought a 3-hp diesel = a
> 3-hp gasoline = a 3-hp electric = a 3-hp anything.  Yes?  No?  Please help me
> out here.  Does this guy know something I don't?
>
> Thanks,
>
> Doug