T-Pain Is On A Boat: [Electric Boats] Re: Regeneration

Wednesday, June 17, 2009

[Electric Boats] Re: Regeneration

Thanks, I think I get it now. The car mileage analogy helps; don't need the physics to be convinced.

md

--- In electricboats@yahoogroups.com, vectorges@... wrote:
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> If you use f=ma then the concept of hull speed is non existant. Drag increases as the square of speed. More drag = more power required. Look at cruising speed requirements. Relatively small increments in speed at the top end require relatively large increases in power requirements. Look at posts in this forum on battery life at higher speeds. Universally you will see that dropping back the cruising speed drastically increases cruising distance (i.e. power usage). Or you could look at automotive MPG ratings at differant speeds. 70 mph uses more gas than 55 mph. I'll see if I can find the physics for you.
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> -----Original Message-----
> From: constancedraper <drmark.draper@...>
> To: electricboats@yahoogroups.com
> Sent: Wed, Jun 17, 2009 8:39 am
> Subject: [Electric Boats] Re: Regeneration
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> I iguess I need a review of college physics. I can't figure out how power required increases as a square of speed. I thought it was a linear function along the lines of F=ma.
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> What am I missing?
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> md
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> --- In electricboats@yahoogroups.com, vectorges@ wrote:
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> > Regen at hull speed is a free lunch. But as you are approaching hull speed it is more like a happy meal. Power required increases as a square of speed, so the faster you go the more power you need. Or, the less speed you lose to regen.
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> > -----Original Message-----
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> > From: constancedraper <drmark.draper@>
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> > To: electricboats@yahoogroups.com
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> > Sent: Tue, Jun 16, 2009 10:02 pm
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> > Subject: [Electric Boats] Re: Regeneration
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> > So, it seems that if you're at hull speed, there is a free lunch, because you can use the surplus motive force to generate electricity instead of piling up a bigger wake.
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> > I'm just a learner here, but I'm not convinced that the 3HP outboard facing the wrong way is a good analogy. First, such a motor only produces an effective 1.5 hp in reverse when you are really hauling. The resistance to forward momentum is, I assume, proportional to forward speed.
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> > Second, I don't think anyone thinks a kilowatt of regen is a realistic design goal unless you're a clipper ship. If you could do an average of 100 watts 24/7 while under sail you'd be producing two or three times as much power as an $800 solar panel. And rather than overcoming a 3 HP outboard motor, you'd only be fighting less than a 1/3 HP motor.
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> > But I admit I'm speaking with the impunity of ignorant inexperience.
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> > md
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> > --- In electricboats@yahoogroups.com, "lon4" <lon4@> wrote:
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> > > --- In electricboats@yahoogroups.com, Arby bernt <arbybernt@> wrote:
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> > > > Regen does not use the straight volts/rpm ratio...
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> > > From one point of view: generating electrical energy requires force. If your sails provide that force and you drag a propeller through the water to generate, that is going to slow the boat down unless you're already at hull speed, and there is a surplus of motive force.
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> > > Rule of thumb is 750 watts/horse power. So, generating 1000 watts (1KW) requires at least 1.5HP of force. I think of it this way: how would you like to drag behind your boat a running 3HP outboard facing the wrong (reverse) direction? Same is more or less true for wind gen's while sailing. You can't get something for nothing. What a DRAG!
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> > > A case for solar, and multi-fuel generator, not withstanding a prop configured to be driven not drive and a separate generator.
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> > > Sailonner
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