It is unfortunate that some in the fledgling electric propulsion industry continue to make such claims.
I would like to point out that we are not ALL doing it. At www.ElectricYacht.
That said, I would like to point out the difference in ratings. ICE's are typically rated in brake horsepower. This is their maximum output without accessories. Often, this is a one hour rating. To get to continous shaft horsepower subtract losses from water pump load, alternator load and transmission. I think 2hp is a good rule of thumb for smaller ICE's. Typically, the continuous rating will be around 80% of this value.
Therefore, a more honest comparison would say that a 5-6 shp electric is equal to an 8-10 bhp diesel. This assumes both are properly installed and matched to the propeller. This is a rough comparison, so don't beat me up over exact numbers.
This is not to say an electric cannot replace an ICE larger than this. But, the user needs to understand the trade offs necessary to gain the benefits of electric.
Until this industry matures and establishes meaningful standards, I would recommend a "buyer beware" attitude. Ask questions and ask for performance predictions and any real world experience with a boat similar to yours. If it sounds too good to be true, it probably is.
Electric power is great, but has its limitations. Understand the trade offs and you will be able to make the right choice.
Regards,
Scott.
--- In electricboats@
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>
> >
> > Technical Specifications of the E-POD 3000 System
> > Operates on 36-48 volts DC (48 volts recommended)
> > AMPERAGE: Peak 200
> > Max continuous 100
> > Recommended Cruise......
> > 40-60 amps @ 48 volts
> > (Performance = to 20 hp outboard / 25 hp inboard)
> >
> > In reading that I can't know what is the max continuous power at the shaft. I have to estimate it : absorbed power 48Vx100A=4800W - a minimum of 15% of losses in the engines and its controller = 4080W or 5,5Hp. So by which miracle a 5,5Hp electric engine can do the job of 25 hp inboard!!!!!
> >
> > >
> > So I can say IT'S CRIMINAL to affirm to the customers that an electric engine of 5.5hp can does the job of a 25hp inboard engine!!!!!!
> >
> > An hp is an hp, there is no difference if the power is produced by electricity, or by humans, or by animals or by petrol or by nuclear, so and so. Behind the power delivers on the shaft the difference depends of the efficiency of the propeller and if the propeller is well adapted with the hull. >
> > Bertrand
> >
> REPLY: I have been an engineer in the electric power industry for over 40 years, and completely agree with your statements. There are rating tricks used by those who want to offer more than what is real within every industry, but claiming that a 5 HP electric drive is the same as a 25 horsepower inboard installation is virtually absurd.
>
> It is indeed possible to mis-design an inboard internal combustion engine installation so badly that it only delivers only 3 or 4 propulsive horsepower to the boat (about what you can get with a 5 HP electric motor and good design practice), but claiming that this is typical practice is just absurd.
>
> In a reasonably designed boat propulsion system, using a low speed large propeller, propulsion efficiency in the 60% vicinity is typical. If you have a large inboard IC engine, use a somewhat mis-matched propeller and gearbox, the propulsion efficiency will be similar, or perhaps a few points worse, but not by a factor of five! The 25 HP inboard IC engine will still deliver well over double the propulsive power available with a 5 HP electric.
>
> Of course, if your four cylinder 25 HP inboard has three of the spark plug wires disconnected, then the claim that the 5 HP electric performs as well may indeed be true.
>
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