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Old 17-08-2007, 17:24   #1
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Windmill-Powered Cat

Has this been posted before:


Revelation II Wind turbine powered sailboat


Windmill powered catamaran. It certainly does nothing for the aesthetics. But then again I gather cat owners don't own mirrors anyhow.....



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Old 17-08-2007, 18:57   #2
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The cat grows on ya after a while.

As for this one? Dang, one drink more than you need and you can clearly lose your head. Literally that is....
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Old 17-08-2007, 19:52   #3
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Quote:
Originally Posted by rickm505
The cat grows on ya after a while.
So do warts.




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Old 17-08-2007, 20:14   #4
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Yeah! It's been posted before.

I can picture that one in a rolling sea.......
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Old 17-08-2007, 21:35   #5
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Bogus!

Quote:
Originally Posted by Tspringer
Has this been posted before:


Revelation II Wind turbine powered sailboat


Windmill powered catamaran. It certainly does nothing for the aesthetics. But then again I gather cat owners don't own mirrors anyhow.....



Terry
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.
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Old 17-08-2007, 23:23   #6
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Are you comparing my boat to one of your warts?
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Old 18-08-2007, 01:32   #7
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Quote:
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.
Extracting energy out of the wind is a function of apparent wind speed. What is the apparent wind speed that you see when you're sitting on the blade of a rotating propellor? What is the most efficient angle to run the propellor relative to the wind? At that point does it matter which direction that the propellor in the water is pushing the boat?

I believe invoking the 1st law of thermodynamics (I think conservation of energy is the one you actually wanted, not the entropy one.) in this way will also require you to believe that sailboats cannot sail faster than the wind.

The interesting argument on the web is whether you can sail faster than the wind dead down wind with this kind of apparatus. In the case of the vehicle travelling faster than the wind dead downwind, the wheels (propellor in the water) is driving the propellor in the air.




I'm still wading through this one, trying to really understand the forces.
Klaus Wiederhöft

This has been discussed to death on other forums, usually with lots of name calling involved. What I would be interested in, is if someone understands the math well enough and his references to propellor efficiency is whether the above author has made mistakes that would invalidate his arguments.

John
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Old 19-08-2007, 09:23   #8
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Damn thing reminds me of a chopper landing I was in... on its side with blades flying everywhere... not something I would ever care to be on... that boat or a helicopter landing on its side. Blades like that flying in front of your face..... gezzz.. me thinks NOT!!
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Old 19-08-2007, 13:11   #9
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Originally Posted by cal40john
I believe invoking the 1st law of thermodynamics (I think conservation of energy is the one you actually wanted, not the entropy one.) in this way will also require you to believe that sailboats cannot sail faster than the wind.
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.


Quote:
Originally Posted by cal40john
The interesting argument on the web is whether you can sail faster than the wind dead down wind with this kind of apparatus. In the case of the vehicle travelling faster than the wind dead downwind, the wheels (propellor in the water) is driving the propellor in the air.
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.
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Old 19-08-2007, 16:05   #10
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There was a forward thinking marine engineer down here in New Zealand several years ago who built up a sloop with a wind prop driving a large diameter water prop through a reduction box, it was so successful that he converted it to a fishing sloop and fished commercially for many years. Of course its best point of sailing was directly into the wind and worst was down wind.
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Old 19-08-2007, 18:50   #11
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It's interesting how words evolve over time.

Originally, a windmill meant just one thing - a devise to harness the movement of air to an apparatus for grinding, or milling grain. Over a long period of incorrect usage, windmill was applied to almost anything that used blades or vanes to create rotation from the movement of air.

On a typical farm, what are called windmills are actually wind pumps - the movement of air is used to create rotation that, in turn, pumps water from the ground.

Similarly, a "windmill" that uses airflow to produce electricity is actually a wind generator.

The "windmill" on the catamaran pictured is actually a propeller; i.e. it uses the movement of air to create motion by turning another propeller below the waterline, through gearing, thereby "propelling" the boat.

It is logical that it would work exactly as envisioned, but all of that windage aloft that can only be reduced in a bad blow with a chainsaw would make me nervous.

TaoJones
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Old 20-08-2007, 00:00   #12
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Does anyone want to guess how much energy is in the wind turbine" when she is turning a few hundred RPM? And anyone who has spun a bicycle wheel and tried to turn it on it's axis will remember gyroscopic precession.

Of course the argument is that it always faces the wind. Right, until the bearing at the bottom of the mast siezes. Then you pull a Fred Flinstone with a rack of dino ribs.

And don't forget pitching seas. Let's see 90 degrees to the axis of rotation ... first surf off a wave flips the boat.

I'd hate to be anywhere near that thing when it's turning.

BTW - I didn't find one scholarly article on this thing. Basically the same "This is cool" blurb at each website with static pictures of the boat at dock. Anyone have anything better or a photo of this thing underway.

I'm starting to think hoax...
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Old 20-08-2007, 00:10   #13
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Quote:
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.
My first thought for the ddwfttw (dead down wind faster than the wind) craft was that is extracting more energy than available also, but the fact that sailboats can sail downwind faster than the wind bothered me. They do it by sailing at an angle to the wind and generating apparent wind. The blades of the propellor are sailing at an angle to the water flow and generating apparent flow. As I said in the previous post it is the propellor in the water that is generating the drive, not the one in the air. So I'm still trying to find some concrete mathematical proof that I can understand before joining the yea or nay sayers.

Is it possible that if you were wrong about going directly upwind, that maybe you missed something in your argument about ddwfttw?

John
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Old 20-08-2007, 01:51   #14
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Originally Posted by Ex-Calif
Does anyone want to guess how much energy is in the wind turbine" when she is turning a few hundred RPM? And anyone who has spun a bicycle wheel and tried to turn it on it's axis will remember gyroscopic precession.

Of course the argument is that it always faces the wind. Right, until the bearing at the bottom of the mast siezes. Then you pull a Fred Flinstone with a rack of dino ribs.

And don't forget pitching seas. Let's see 90 degrees to the axis of rotation ... first surf off a wave flips the boat.

I'd hate to be anywhere near that thing when it's turning.

BTW - I didn't find one scholarly article on this thing. Basically the same "This is cool" blurb at each website with static pictures of the boat at dock. Anyone have anything better or a photo of this thing underway.

I'm starting to think hoax...
Not of Revelation, but:

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Old 10-07-2009, 15:10   #15
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Not an overunity device

The windmill powered boat going against the wind does not violate the conservation of energy law. I believe the confusion relating to this topic is the fact that people are confusing over all energy with net force. Consider the equation E=F x d, where E = energy d = distance and F is force. Now consider the fact that the boat is actually travelling in two media (Air and Water) with(on a windy day) differing relative velocities to each. Now while the underwater propeller must create a greater force then the opposing force on the wind turbine a greater energy may still be imparted from the flowing air to the wind turbine than is imparted from the propeller to the water as the distance travelled by the turbine through the air medium is much greater(relativistically speaking) then the distance travelled by the propeller through the water. It is down to the fact that momentum and kinetic energy are two different things. For instance a larger mass of propelled water my have greater momentum and hence provide a greater reaction to the boat but have a lower kinetic energy than a lesser mass of faster moving air.
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