Hello,
To be correct, Physics wish, 1 hp = 746 watts, but then electric power is more efficient because power is more related to torque than high RPM, so, as a rule of thumb, an electric HP does the same push as 2 ICE hp because it uses the propeller more efficiently, on most of the RPM range, except at high RPM, where the ICE propeller is generally matched to the ICE engine.
To make a long story short : the power curve of the Electric engine is more closely related to the power transmission curve of propellers than the ICE engines which tend to have all there horses at high RPM, so the advantage. Electric shines when you turn a large propeller slowly.
Hence "1000w = 3 HP" is a good "engine swap equivalence" but not a "true" equation, from the Physics point of view.
Serge
--- In electricboats@
>
> 1000w = 3hp so you need a 66kw motor.
>
>
> On Apr 9, 2010, at 12:10 PM, Joe Salzetti wrote:
>
> >
> > Have the same question but for a 200hp gas engine?
> > Also how many batteries would I need?
> >
> > Thank you!
> > Joe
> >
> > Sent from my iPhone
> >
> > On Apr 9, 2010, at 9:50 AM, "Eric" <ewdysar@...
> >
> >>
> >> Dan,
> >>
> >> So what size electric motor would you suggest to replace a 100hp engine in a power boat? (assuming that the engine was appropriately sized)
> >>
> >> Eric
> >>
> >> --- In electricboats@
> >> >
> >> > It's not so much a matter of efficiency, since horsepower is measured at the output shaft and any inefficiencies are already taken into account. Rather, it is a matter of the power curves. An ICE's HP is rated at WOT where it produces max HP, but torque is usually starting to drop. Plus, an electric motor's HP is rated at the point were it can run all day without overheating. The fact is, electric motors can be run at higher rpms, and therefore higher HP, for a short period of time. You can use this limited service factor for conditions where you want more HP, such as maneuvering or emergencies.
> >> >
> >> >
> >> >
> >> > --- In electricboats@
> >> > >
> >> > > You are correct. People will usually figure that an electric drive will be 2 to 3 times as effficient as an ICE engine in converting energy into thrust, due to less energy lost as heat. Therefore, a 100hp gas or diesel engine can usually be replaced with a 35-50hp motor with similar performance results. Unfortunately, a 50hp motor will draw at least 38kW under full power, which translates to 380A at 100V. So these kinds of power ratings require even higher voltages to keep the amperages reasonable. That doesn't even begin to address the problems of energy storage...
> >> > >
> >> > > Fair winds.
> >> > > Eric
> >> > > Marina del Rey
> >> > >
> >> > > --- In electricboats@
> >> > > >
> >> > > > I thought that I read that a 100 hp motor would be the same as a 200 hp gas engine?
> >> > > >
> >> > > > Sent from my iPhone
> >> > > >
> >> > > > On Apr 7, 2010, at 9:44 PM, "peoria_diver" <daredster@> wrote:
> >> > > >
> >> > > >
> >> > > > Denny,
> >> > > >
> >> > > > Following sugestions from this group, I did a little online shopping today. Powerboat hulls just don't seem like good candidates to me. Even small trawlers have engines in the 100HP range. I switched back to sailboats and found a couple of centerboard boats at 28'. I am still a little concerned about the stability. I'll have to give it some thought.
> >> > > >
> >> > > > -Red
> >> > > >
> >> > >
> >> >
> >>
> >
> >
>
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