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I've got a small speedboat that will do slightly over 40 mph on a calm inland lake, the notion that this can cruise at a similar speed is astonishing giving its size and open ocean conditions.

It's not that astonishing. The main speed constraint on a displacement hull like an ocean liner's is the bow wave. As a ship moves forward, the water it pushes aside has its pressure increased slightly, so it bulges upward at the bow. What goes up must come down, so this bulge eventually drops down to sea level, then overshoots and drops below sea level. This is called a bow wave. The key here is that this motion of this wave is dictated purely by the physics of the water (and the water depth, but that effect is small enough it can be ignored in the ocean). And that the front of this induced pressure wave is stuck to the bow of your ship (it's a standing wave when viewed from the ship), hence why it's called a bow wave.

I'll skip the math, but the net effect is that at slow speeds, your ship is moving through multiple waves of its own creation and stays relatively level. But at a certain speed called the hull speed, the wavelength almost exactly matches the length of the ship, and the bulk of the ship's mass sinks down into the trough of its self-induced bow wave. At that point, your ship is basically trying to power itself "uphill" through the water (opposite of surfing), and the energy required to move faster increases dramatically.

There are two ways to bypass this problem.

• Stop displacing water. That's what your speedboat does. At speeds above about 20 knots, it starts planing on top of the water, instead of forcing its way through it. This lifts the hull out of the water, and thus no more standing wave problem.
• Make the ship longer. The longer the ship is, the faster it can go before this standing bow wave lengthens to match the length of your ship. This is how displacement ships like ocean liners, cargo ships, and navy ships get around the problem. (Actually the nuclear powered navy ships can just increase energy output to power through this - it's not an absolute limit like the speed of light; and if you go fast enough the back of your ship climbs higher out of the trough so the energy requirement decreases).

This is also the rationale for the bulb underneath the bow of large oil tankers and cargo ships. It's location underneath the water slightly forward of the ship makes the water act as if the ship is slightly longer (the bow wave starts earlier), allowing it to eek out a tiny bit more speed at the same amount of wave resistance.

A good explanation should go to the heart of the paradoxes, which are these: how can you power the motion of a cart by extracting power from its motion? How does taking power from the wheels lead to power being extracted from the wind? Your first attempt at an explanation looked like just a collection of factual inaccuracies, non-sequiturs and assertions to be taken on faith (like all the others here and in many other places), but I have to admit that within this version, you have the best simple explanation that I have seen. All you needed to write was this:

Consider a cart going 30 feet per second in a 20 foot per second MPH wind. The car is going 10 feet per second faster than the wind, so there's 10 feet per second of air going through the prop. Lets put one pound of drag on the wheels. Again, power = force * velocity. Power = 1 pound * 30 feet per second. The drag at the wheels generates 30 foot-pounds per second of power. We feed that 30 foot-pounds per second of power into the prop. Power = force * distance. The distance is 10 feet per second of air through the prop, so we have 30 foot-pounds per second = force * 10 feet per second. Solving that we get Force = 3 pounds. The prop can covert that power into up to 3 pounds of thrust. Even if the prop is only 50% efficient, it's still generating 1.5 pounds of thrust. The cart is going faster than the wind, and accelerating.

You follow this by comparing it to a lever, which makes your explanation look bogus because we all know that you can't construct a system of levers that moves itself. A few numbers are more convincing than any amount of hand-waving 'explanations' like "would have to spin crazy fast..." This is a case where more (sentences) is less (of a plausible explanation).

This explanation could be strengthened with an estimate of achievable power-to-thrust ratios for the propeller, but with airfoils being capable of lift/drag ratios of 50, I don't doubt that it would be satisfactory. A calculation of the power balance would also help, but that has already been done: while the papers you link to discuss the conditions that need to be satisfied without showing that they can be, this one does.

There is also a much better video than any I have seen of the Blackbird, from a different team with a different machine. Putting streamers outside of the stream-tube that goes through the rotor, and with one high enough to demonstrate that wind shear is not a factor, is convincing. In contrast, the Blackbird team attempted to demonstrate the relative wind in a truck that alternately fell behind and caught up with the cart. They only had a couple of shots of the wind vane (none during most of the FTW part of the run), and you cannot tell if these were during the periods when the cart was catching up with the truck or if the wind was gusting (the BUFC have another video here which shows the cart passing a flag that shows the true wind direction. It would be nice to have a sequence of airspeed readings from pitots mounted at the streamer positions, together with the corresponding ground speeds.)

This is moot, but I have no idea where you got the idea that airplanes need millions of horsepower. WWII fighters were in the 2000 - 5000 hp range, while the F1 racing planes are using hundreds rather than thousands of horsepower. A high-performance sailplane dissipates about 2hp at its most efficient speed, around 60 mph.

The reduction of efficiency of propellers at low airspeed is a general effect, and I believe it is mostly due to recirculation of the airflow at the tips.

So here's a question for everyone: could you make it work in a boat?

Yes.

Here's an analysis performed by Mark Drela of MIT (http://web.mit.edu/aeroastro/people/drela.html)

http://www.boatdesign.net/forums/attachments/propulsion/28167d1231128492-ddwfttw-directly-downwind-faster-than-wind-ddw2.pdf

Thanks for rehashing basically the entire debate.

However, there's one hitch. They've already done this out on the salt flats with an actual person in the vehicle, and done it dozens of times in front of hundreds of people. No tricks, a very simple mechanism. It isn't perpetual motion any more than a DN Iceboat that can go insane speeds of 70+ mph in a breeze of 20 - downwind.

In addition, you'll find hundreds of pages of discussion on sailing websites. Specifically here:
http://forums.sailinganarchy.com/index.php?showtopic=82175

The engineers who put that machine together are there. I've talked with them dozens of times and they've explained literally every step of their process. You'll find no end of skeptics - right up until the point where they start posting videos of them actually doing it. There's nothing secret here, they'll explain it right down to the nuts and bolts so you can build your own scale model to prove it to yourself, on a treadmill or in the real world.

This isn't perpetual motion. It's elegant engineering. There have been boats in the water developing this same concept (though they can't go dead down wind yet) for a long long time.

http://www.navagear.com/wp-content/uploads/2007/02/windowslivewriterwindturbinepoweredsailboat-1270awindmill-boat-thumb51.jpg

http://www.boatdesign.net/forums/attachments/projects-proposals/13565d1180209267-windmill-wind-turbine-powered-boats-how-many-out-there-they-viable-vertical_windmill_catamaran.jpg

Their main issue with going DDW is the losses incurred because of the friction with the water. The ground (or even ice) is far less lossy in transferring the power from the wind-driven motion back to the vehicle.

http://www.bricsys.com/en_INTL/bricscad/features.jsp

http://www.boatdesign.net/forums/

http://www.touchcad.com/tc3features.html

http://www.touchcad.com/tc3news351.html

See 3/4 of the way down on this for OpenGL rendering
http://www.touchcad.com/tc3news35.html

Possibly dated review:

http://software.techrepublic.com.com/abstract.aspx?docid=599221

This one:

ProgeCAD, is kinda interesting. It has a layer management system that is different from but kinda similar to ACAD. I tried it last year, but then it timed out on me. It's free for academic use, otherwise, starts about $250 depending on the version, IIRC. It's one of those that seems to be an ACAD knock-off, but kinda updated or less crufted than ACAD 2007/2008 maybe due to a cleaner, newer codebase (as opposed to, say, accumulating decades of in-fighting over code functions, (my ACAD course instructor in 07 said ACAD))

http://www.progecad.co.uk/Downloads/

Also, consider ViaCAD

http://www.punchcad.com/products/viacad2d3d.htm

Their prices are pretty good, and if you're not needing the overkill of ACAD and not working with clients who DEMAND ACAD, and who live with DXF/ACIS formats that contain the info, then why get addicted to a product that costs a fortune to use legitimately. You have rake in some serious dough to justify paying $4k+ on software which can take years to get proficient with. ViaCAD is GREAT for me for lofting/surfacing & solids-making.

Right now, the ship design industry (maybe, based on the economy now, compared to last year) is short on designers/drafters who are GOOD at CAD. If you're designing real or model boats for sale as kits (or ships & boats to be built) check out the combination of delftship and Punch ViaCAD...

Also, see boatdesign.net

http://www.boatdesign.net/forums/design-software/

and...

http://www.polycad.co.uk/links.htm

GOOD LUCK!

http://www.bricsys.com/en_INTL/bricscad/features.jsp

http://www.boatdesign.net/forums/

http://www.touchcad.com/tc3features.html

http://www.touchcad.com/tc3news351.html

See 3/4 of the way down on this for OpenGL rendering
http://www.touchcad.com/tc3news35.html

Possibly dated review:

http://software.techrepublic.com.com/abstract.aspx?docid=599221

This one:

ProgeCAD, is kinda interesting. It has a layer management system that is different from but kinda similar to ACAD. I tried it last year, but then it timed out on me. It's free for academic use, otherwise, starts about $250 depending on the version, IIRC. It's one of those that seems to be an ACAD knock-off, but kinda updated or less crufted than ACAD 2007/2008 maybe due to a cleaner, newer codebase (as opposed to, say, accumulating decades of in-fighting over code functions, (my ACAD course instructor in 07 said ACAD))

http://www.progecad.co.uk/Downloads/

Also, consider ViaCAD

http://www.punchcad.com/products/viacad2d3d.htm

Their prices are pretty good, and if you're not needing the overkill of ACAD and not working with clients who DEMAND ACAD, and who live with DXF/ACIS formats that contain the info, then why get addicted to a product that costs a fortune to use legitimately. You have rake in some serious dough to justify paying $4k+ on software which can take years to get proficient with. ViaCAD is GREAT for me for lofting/surfacing & solids-making.

Right now, the ship design industry (maybe, based on the economy now, compared to last year) is short on designers/drafters who are GOOD at CAD. If you're designing real or model boats for sale as kits (or ships & boats to be built) check out the combination of delftship and Punch ViaCAD...

Also, see boatdesign.net

http://www.boatdesign.net/forums/design-software/

and...

http://www.polycad.co.uk/links.htm

GOOD LUCK!

My biggest problem with the Volt is that it's damn ugly. Sort of reminiscent of muscle cars, which I despise.

I was kind of like a motor head and love muscle cars. A friend's dad had a '68 or '69 Grand Prix he put a big block 350ci with bored out cylinders into. We'd hop into it and cruise to a shooting range at 120 mph where we target practiced. I loved that car, and shooting. My problem with them is that they're gas guzzlers. Though I love racing I have the same problem with race cars. But at least those can be used to test new ideas, whether to improve efficiency or safety.

All I ask for, from any company, is a plug-in hybrid Cabriolet or Roadster.

I'd rather have a cigarette boat with a Tesla like motor.

Falcon

I dunno about that theory, but as a serious offshore fisherman, I'm getting killed by fuel costs. my boat has a couple of "efficient" yamaha 4 strokes, and I get 1.2 - 1.5 mpg. Lower if it's windy. I'm selling it this year. These guys are on the right track with the sails. Maybe This is the solution: http://boatdesign.net/forums/showthread.php?t=1147 9&page=9 "The relatively small size of our engines, and the improved drive and hull efficiencies, make for a fuel miserly vessel that attempts to break the vicious circle of needing more fuel to power the higher h.p. engines needed to carry more fuel. This speed/fuel dilemma is discussed in an article in MARLIN, Feb-Mar '93. A more recent issue of MARLIN, Jan '95, makes a "head to head comparison" between a traditional 50' sportfisher, "Kelsey Lee" and a 50' catamaran vessel,"Tara Vana" over an identical, non-stop, 900 mile course from Costa Rica to Mexico; 1800 gals of fuel verses 320 gals for the cat (under power for the entire trip). And Tara Vana was able to fish the entire trip, unimpeded by the extra fuel containers which filled up the cockpit of Kelsey Lee. On another occasion, a voyage of 3700 miles was accomplished with the consumption of only 195 gals of fuel! [ The savings in fuel cost alone could defray a substantial portion of the crew salaries of this vessel in charter]" http://www.runningtideyachts.com/articles/TaraSoun dings.html