I'm curious to know if anyone can tell me how much energy(percentage-wise) 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-wise)an electric motor running at much less than hull-speed begins to somewhat approach the economy(energy-wise ) of an 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@yahoo.com > wrote:
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
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