I too have heard that at speeds less than hull speed that electric is 4 to 6 times more efficient than ICE but that may just be misremembering what I read.
A big advantage of electric is the ability to recharge via wind and solar. It is quite hard to make gasoline on your boat....you need to carry a 50 ton minimum drilling rig, a processing plant (maybe 100 tons?), and then of course you would have to be in a spot that has oil. :-)
But seriously, 2KW of solar would be 12KWH per day minimum in the tropics, which would be like regenerating 1 gallon of gasoline a day for about 300 pounds of panels. If gas is 8 pounds per gallon, then on a 40 day trip the panels win out over the weight of the fuel. At $3 a watt the panels would be pricey, but they do last 25 years...
Instead of thinking about carrying 8 tons of batteries and comparing that to ICE, what about carrying a means of regenerating a smaller bank of batteries, via wind or solar?
--- In electricboats@
>
> I'm curious to know if anyone can tell me how much energy(percentage-
> of top-rated energy(such as optimum RPM's for an IC motor & optimum RPM's
> for an electric motor), a 26 boat(5000k) running at 1/2 hull speed, would
> require with a gasoline engine and an electric motor, respectively.
>
> I know the answer is dependent on more information, but what I'm trying to
> compare is if the economy(energy-
> than hull-speed begins to somewhat approach the economy(energy-
> IC engine, since the IC engine seems to require much more speed(RPM's) for
> the same amount of torque of an electric motor.
>
> I'm hoping that the electric motor will result in a much lower percentage of
> the optimum/maximum to go 1/2 hull speed than a gasoline engine would, such
> that an electric motor at the lower speeds might be 5, 6 or more times more
> efficient than an IC engine would be.
>
>
> Just curious
>
> John Francis
> Pearson 26
> Port Clinton, Ohio
>
> On Thu, Apr 8, 2010 at 2:35 PM, Eric <ewdysar@...
>
> > Since we typically get new people on the list, I thought that it would be
> > helpful to post some basic info about electric drive systems that should
> > help get people's heads wrapped around this technology.
> >
> > A quick introduction to electric power concepts and terms:
> >
> > Energy is the ability to do work
> >
> > Power is the rate at which work is done
> >
> > Energy is related to your electricity storage, i.e. batteries. The size of
> > your energy storage directly relates to your boat's range.
> >
> > Power is related your drive system. The rated size of your drive directly
> > relates to your boat's cruising speed and acceleration under power.
> >
> > Energy equivalents: Gasoline contains about 33kWh of energy per gallon.
> > Diesel is more dense and contains about 38kWh of energy per gallon.
> >
> > A 48V battery bank that is rated for 200Ah stores about 10kWh of
> > electricity. Most comparisons between electric and ICE drive systems figure
> > that electric drives are 2 to 3 times more efficient than fueled engines.
> > If one considers electric drive 3 times as efficient, then the battery bank
> > mentioned above holds energy equal to just less than 1 gallon of gasoline
> > and only ¾ of a gallon of diesel. This is only true if one is wiling to
> > drain the battery bank completely, doing so repeatedly reduces the life span
> > of the batteries. Depending on the battery chemistry, accepted levels for
> > depth of discharge (DOD) are from 50% to 75% of rated capacities.
> > Therefore, a typical 48V 200Ah battery bank and electric drive has about
> > the same usable energy as ½ gallon (2 liters) of gasoline through an ICE
> > engine. A wet cell or AGM battery bank of this capacity weighs about 500
> > pounds (225kg).
> >
> > Please feel free to correct any misconceptions, or add any additional basic
> > considerations for those that are thinking about converting to electric
> > drive.
> >
> > Fair winds,
> > Eric
> > Marina del Rey
> >
> >
> >
> > ------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>
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