Re: [PSUBS-MAILIST] Horsepower

["Marsee Skidmore" <heyred@email.msn.com>]

The difference is in how the ratings are done. Electric motors have a fairly
linear power curve (hp vs. rpm), and are derated for continuous duty. In
other words, the rated horsepower of an electric motor is on the low end of
the output curve, just to be conservative. Internal combustion engines have
a very peaky power curve, and are rated by the peak output. Conservative,
conshmervative, let's sell cars! Race car drivers like to run at the peak of
the power curve, but those of us who pay for their own gas and overhauls
operate a little bit further down on the curve. Three to one sounds about
right. A 60 hp Volkswagen runs just fine with a 20 hp electric motor. - Joe
----- Original Message -----
From: <SeaLordOne@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, January 26, 2000 5:59 PM
Subject: [PSUBS-MAILIST] Horsepower


> 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
>