Windmill-Powered Cat

[Robertcateran]

Originally Posted by GreatKetch

Maybe I am just getting suspicous in my old age, but my bogosity meter is running pretty high on this one. Certainly their claim that they are at the most efficent going straight into the wind violates the 2nd law of thermodynamics. A wind powered craft CAN NOT go straight into the wind.

I strongly suspect that boat was designed and built on a Photoshop screen.

Yes it can, based on the same principle that allows tacking into the wind

[Robertcateran]

Originally Posted by GreatKetch

Actually it is the 2nd law that applies here, that's the one that proves you can't have a perpetual motion machine. In a very simple form the 2nd law says that you can't convert energy from one form to another without an increase in entropy. That increase in entropy comes at the expense of the available energy. Lot's of people throw around the 2nd law, but is is definetly one of those things that you need to understand the mathamatics to really "get it." Words just can't convey all the implications.

And it has nothing to do with sailing faster than the wind, unless you are sailing downwind Even if you had a 100% efficent windmill and a 100% efficient water prop all the energy you get from the windmill comes at the expense of drag. The more energy you get out, the more drag. You can never overcome that drag.




That's hardley an interesting argument, because it is just plain wrong. We don't need higher math or anything about propeller efficiencies. Let's do an Einstein thought experiment for a moment.

We have our windmill powered boat headed down wind. The mill is turning and the propeller and we start moving. The faster we move the slower the apparent wind. The slower the apparent wind the less energy that we can extract from it. Eventually the energy available is equal to the friction of the boat through the water and we stop accelerating and move at a steady speed. We can't go any faster than that.

I guess people can call each other names all they want, but fortunetly the physics doesn't change no matter how nasty the names.

The physics that allow ice boats to go down wind faster than the wind by tacking allows a craft to go downwind faster than the wind. The energy is extracted from the difference of the speed of the air compared to the surface the craft is travelling on. It took me a little while to come to terms with this but if you start working on the forces on the iceyachts, and transfer the same principles of tacking downwind to an efficient windmill transferrring its forces via an efficient system to wheels or propellors on or in the relatively fixed medium then it starts to make sense.

[Billygroin1666]

Sure you can head downwind faster than wind with a windmill powered boat.
In this case one must have an underwater propeller with a lower resistance but a high rotation rate and the and a windmill that can push a mass of air that has greater momentum(but lower kinetic energy) than the smaller mass of water which is moving at a higher relative velocity to the ship than the air's velocity relative to the ship. In general low water drag will help here. The ship now has the input energy coming from the water rather than the air and the output pushing force is instead supplied by the windmill(or fan) in this case. Using hydrofoils with just the low drag input rotar underwater as well will help to make this more achievable as the drag created by the water will increase a lot at speed. Overall the energy is essentially sourced by having two different media with different velocities relative to each other and all work done by vessels as described will decrease the overall movement between the atmosphere and oceans (by a miniscule undetectable amount). In a hypothetical case where the sun(weather driving force) were to die of and you could avoid the problem of the atmosphere and ocean freezing then the earths rotation would exclusively provide currents in the atmosphere and ocean. Using just these machines to produce work would over time only serve to slow the rotation of the earth indirectly via reactions applied to the atmosphere and ocean you would eventually end up with a non rotating planet without weather. I hope this unrealistic example sheds some sort of light on where what is sometimes percieved as free energy is actually sourced from.

[drdrdlm]

Originally Posted by GreatKetch

Maybe I am just getting suspicous in my old age, but my bogosity meter is running pretty high on this one. Certainly their claim that they are at the most efficent going straight into the wind violates the 2nd law of thermodynamics. A wind powered craft CAN NOT go straight into the wind.

I strongly suspect that boat was designed and built on a Photoshop screen.

No. It exists. I have seen it, though only at the wharf.

You later said:
And it has nothing to do with sailing faster than the wind, unless you are sailing downwind Even if you had a 100% efficent windmill and a 100% efficient water prop all the energy you get from the windmill comes at the expense of drag. The more energy you get out, the more drag. You can never overcome that drag.

I think the error here is that the wind turbine does not generate energy from drag, but from lift. The blade is a wing, and is rotated by the lift, which can be much larger than the drag. It is a fascinating concept.

David

[Steve Pope]

There has been a very sucessful monohull with a windriven propellor that was in use for many years, Built by a very clever engineer (Jim Bates) here in New Zealand, in its later life it was used as a commercial fishing boat (longlining) It was wrecked after dragging its anchor onto rocks.
Another more recent version, a windriven cat wasn't so successful, It used an A frame mast setup but suffered badly from vibration. It has been converted back to sail still using the A frame though.

[Steve Pope]

Below is a thread re Jim Bates history, with family input.

New Zealand made bronze winches