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.
-----Original Message-----
From: constancedraper <drmark.draper@
To: electricboats@
Sent: Tue, Jun 16, 2009 10:02 pm
Subject: [Electric Boats] Re: Regeneration
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.
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.
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.
But I admit I'm speaking with the impunity of ignorant inexperience.
md
--- In electricboats@
>
> --- In electricboats@
> >
> > Regen does not use the straight volts/rpm ratio...
>
> 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.
>
> 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!
>
> A case for solar, and multi-fuel generator, not withstanding a prop configured to be driven not drive and a separate generator.
>
> Sailonner
>
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