Most sail boats have a small gas powered engine, used for emergency situations, and navigating in and out of the docks.

This sail boat would use a battery instead of a normal gasoline powered engine. The battery would be recharged by a windmill adhered to the top of the boat, or a similar device under the boat. Either way the motion created by the boats propulsion would then recharge the battery.

This saves money, gasoline, and the ocean.
-- ColonelMuffins, Mar 20 2007

Halfbakery: Whirlyboat Whirlyboat
Without a sail. [jutta, Mar 20 2007]

Physics of Sailing http://www.phys.uns...au/~jw/sailing.html
Why it's possible to sail faster than the wind. [csea, Mar 20 2007]

I'm for anything that will save the ocean....that's why I like tuna so much....I suspect tuna flatulence is destroying the ocean...I'm doing my part by eating the critters that do that.
-- Blisterbob, Mar 20 2007


Windmill generators for sailboats are so baked. "Sailboat Wind Generators - A wind generator is a critical component for sailboats."
-- baconbrain, Mar 20 2007


// Either way the motion created by the [boat's] propulsion would
// then recharge the battery.

If the motion is caused by the wind, the boat tends to move with the wind, not against it; thus the propulsion of the boat makes the wind relative to the boat slower, not faster, and takes energy away, rather than producing it.

The reason that wind generators nevertheless work in practice is that there's usually plenty of wind left over.

[... and all that turns out to be wrong. See csea's correction, below.]
-- jutta, Mar 20 2007


Interesting point jutta. I didn't consider the physics of that. However the idea of putting a windmill under the boat, that spins because of the boats forward motion, would still function.
-- ColonelMuffins, Mar 20 2007


The amount of extra air flow is more than sufficient for this task due to the extra drag from the water, hot air balloons is another story.
-- jhomrighaus, Mar 20 2007


// I didn't consider the physics of that.// Look like you'll fit right in here, Muffin.
-- MaxwellBuchanan, Mar 20 2007


[jutta]

//If the motion is caused by the wind, the boat tends to move with the wind, not against it; thus the propulsion of the boat makes the wind relative to the boat slower, not faster, and takes energy away, rather than producing it.//

You've cited the case where the apparent wind is less than the land-based wind, but it's entirely possible to make the observed windspeed at the sailboat exceed the land-based wind, often by a fairly large factor, by "tacking." See [link].

While a wind generator might slow the boat by a small amount, It's certainly possible to extract useful energy, charge a battery bank (the extra weight could be in place of the heavily weighted keel) and potentially run a small electric engine, when the wind dies down.
-- csea, Mar 20 2007


That makes sense. Thanks for the explanation!
-- jutta, Mar 20 2007


[jutta] Happy to help.
-- csea, Mar 22 2007


This is all probably quite feasable, and more or less baked in pieces, though not widely known to exist by any stretch of the imagination.

Windmills on boats are quite common, and some boats connect their propellor shafts up to turbines so they can generate electricity when a stiff current is going... or when the sails are pushing the boat through the water.

There was even a japanes guy that put a windmill up to an electric motor, and averaged... five to ten knots.

So yeah, this is totally possible. However, the fact that it isn't done much suggests in my mind that there is a reason it is not done much.

Possibly this reason has to do with the corrosive nature of sea water, and the typically unreliable electrical systems onboard some private yachts.

Who cares though. I'm not rich enough for a yacht, right?
-- ye_river_xiv, May 12 2007



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