Hi Dick,
You make some valid points, but if you are going to take into account all the electrical losses along the way to your battery charger, you should also include all the losses gasoline has on the way to your fuel tank. For example, the energy used transporting the crude oil, the energy used refining, the energy used transporting the refined gasoline (or diesel), etc, etc.
Pat
--- In electricboats@yahoogroups.com, Richard Byrd <dick@...> wrote:
>
> Mark:
> I agree with your points on the advantages of electric power over fossil-fuel power, EXCEPT for the efficiency issue. This is a complicated question, and I fear that your answer is too simple. I agree that an IC engine only uses some 30% of the energy in the fuel to produce horsepower at the shaft, and the rest is wasted, but the analysis with electric motors is more difficult. Generally we are charging our batteries from the electric grid, and that electricity is produced from a fossil fuel. Power plants are more efficient than is a an ICE, so the power plant gets maybe 50% of the input fossil-fuel energy into power at the generator head, BUT THEN, that electricity suffers big-time transformer and line losses in getting to your house. THEN, you use it to charge a battery, and you suffer electric-to-chemical conversion losses there. THEN, you convert the batteries chemical energy back to electrical and put it into your boat's electric motor. THEN your electric motor losses some energy converting from electric finally back to mechanical energy. My analysis is that you will be getting much LESS than 30% of the power-plant's input energy as output shaft power at your boat motor. I think you would be lucky to get 5% of the power plant's energy showing up at your shaft.
>
> Does anyone know of a very thorough analysis done on all this conversion loss problem?
>
> Dick
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> On Jan 24, 2011, at 12:00 PM, Mark n Angela wrote:
>
> > Roger,
> >
> > Welcome. As Steve indicated, your 6hp motor is mostly a 6hp motor, not a 6hp propeller. Manufacturers usually measure the motor's horsepower without gears and oil pumps and water pumps and alternators and any other incidental engine load. So electric repowers are usually about 1/2 the watts (horsepower), a little more or less depending on the guessed old efficiency and the guessed or calculated new efficiency. Propeller diameter and RPM make the biggest difference (bigger and slower are most efficient).
> >
> > The other part of your question: "is electric power more efficient?"
> > There are several answers:
> > 1. YES, because there is no idling wasted energy.
> > 2. YES, because you use exactly the power you want, when you want (you are not confined to minimum RPMs).
> > 3. YES, because internal combustion engines (ICE) can only harness 10% - 30% (ballpark) of the energy of the liquid fuel, and electric ones get 70% - 90% (ballpark) harness.
> > 4. YES, because the maintenance cost of electric is roughly one tenth the yearly cost of ICE maintenance.
> > 5. YES, because sailors end up sailing much more and motoring much less (starting an ICE is problematic, starting an electric is quick).
> >
> > Questions are good,
> > Mark Stafford
> >
> > --- In electricboats@yahoogroups.com, "roger_russelburg" <rrusselburg@> wrote:
> > >
> > > Hi
> > >
> > > I am new to this group.
> > > My sailboat works fine with 6hp outboard.
> > > Is there direct relationship (6hp = 4750w) or is eletric power
> > > more efficient?
> > >
> > > Maybe this to complex for a simple answer.
> > > Point me in right direction.
> > >
> > > Thanks
> > > Roger Russelburg
> > >
> >
> >
>
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