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I was disappointed that there was no coverage of the America's Cup match race that the American team BMW Oracle won in a best of three match. Actually as I read it was no race at all as the Oracle won race one by over fifteen minutes and then swept the competition by winning race two.
OK this is not your "normal" America's Cup yacht. It had trimaran hull with a fixed wing sail was 223 feet tall.
What I don't understand is the claim it could sail three times FASTER than the wind speed. This to me defies the laws of physics. It's like it is generating more power that it is consuming which it the definition of the impossible perpetual motion machine.
Can anyone explain how this is possible?
Here is a link to see photos of the Oracle. It is amazing. If you want one I believe it only cost around 33 million.
http://bmworacleracing.com/en/inter...ml?track.refer=/en/index.html&track.type=home
 

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I was disappointed that there was no coverage of the America's Cup match race that the American team BMW Oracle won in a best of three match. Actually as I read it was no race at all as the Oracle won race one by over fifteen minutes and then swept the competition by winning race two.
No coverage? :laugh:

Then you must not have read my posts :horn: in:

http://justlabradors.com/forum/thre...-4-America-s-Cup-has-just-ended-The-winner-is

ETA: See also http://www.nytimes.com/2010/02/15/sports/15cup.html?ref=sports

What I don't understand is the claim it could sail three times FASTER than the wind speed. This to me defies the laws of physics. It's like it is generating more power that it is consuming which it the definition of the impossible perpetual motion machine.
Can anyone explain how this is possible?
Maybe you're thinking that if the wind blows 10 mph, then the fastest a boat could move would be 10 mph downwind minus whatever penalty there is for the friction of the hull moving through the water?

BUT downwind is one of the slowest points (directions off the wind) for a sailboat.

The flexible sails of a boat are constructed to be in the shape of an airfoil, like the upper surface of a airplane's wing, when properly positioned relative to the wind. When they're too parallel to the wind, the fabric flutters like a flag in a stiff wind. The desirable, most effective position is to move from a parallel position to one in which the sail no longer flutters but assumes its desired airfoil shape -- and not one whit farther.

When they're set in the proper position relative to the wind, they generate lift on their leeward side as well as respond to the pressure on their windward side. For that reason, sailboats sail their fastest on a beam reach (a course 90º to the wind) or on a broad reach (slightly more than a right angle to the wind). Whatever course they're on, the sails must be continually adjusted to only just barely be on the edge of fluttering (sailors call this fluttering "luffing") in order to maximize both the lift and the push.

That's the reason that most fast racing sailboats never sail straight down wind because then they would be limited to the wind's speed minus the penalty for the drag from their hulls. Instead, they sail zig-zag courses so they can take advantage of the lift generated on the leeward side of their sails as well as the push on the windward side. Sailing zigzag makes for a longer distance to sail but it's so much faster, it's worth it.

If your reasoning was correct then sailing iceboats wouldn't be able to go faster than the wind, either, would they? But they're capable of speeds over 60 mph in 15+ mph winds because they use the same forces I've described above BECAUSE their skates on ice have such little resistance to movement (unlike the typical sail boat's hull through the water).

ETA: for speeds much faster than the wind (up to 10X) see: http://en.wikipedia.org/wiki/Iceboat

Alinghi and BMW Oracle are not typical sailing monohulls.

Oracle is a trimaran (3 hulls) and designed to often "fly" its center (largest) hull and also its windward pontoon/ama thereby reducing friction enormously by having only its leeward pontoon/ama in the water. In doing this, in reducing the friction so much, it becomes quite a bit closer to the 60+ mph sailing iceboats.

Alinghi is a catamaran (2 similar hulls) and operates very similarly, often flying its windward hull.

Why Oracle is so much faster than Alinghi may OR may not have been because she was a trimaran. Perhaps it was primarily because Oracle used a newly developed wingsail? Or some other innovation? Or some combination of designs and innovations?

The jury is out and these matters and consequences will be discussed and argued for years -- and countless designers will use some of this feature, some of that, and maybe, in 50 years, we'll have a better idea of what contributed how much to the final speed difference?

 

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As Bob said, it's all about the relationship between lift and drag. The Americas Cup boats have very low drag and very large, very efficient airfoils (sails). In all points of sail except directly downwind, the sail "pulls" the boat through the water so top speed isn't limited by windspeed as much as it is by the pressure differential generated by the lift of the airfoil. Only when sailing downwind is a boat "pushed" through the water, where sails function more like parachutes, is top speed strictly limited by windspeed (minus drag of the hull, etc.).

Still, it's mind-boggling to think of being able to do 30 kts in 10 kts of wind. Most conventional sailboats (like ours) can't come close to even sailing the windspeed. But most boats' top speeds are a function more of their hulls (hull shape, keel type, and water line) than their sails, e.g. the drag effects override the lift.
 
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