Posted: Mar 05, 2011 8:19 am
Wrong. True wind is the velocity difference between air and surface. Velocity and force are different physical quantities.
The_Metatron wrote:it has both magnitude and direction.
Yes, true wind is a vector. See the vector diagram:
As you see the vector component of the vehicle's velocity in the same direction as the true wind(downwind VMG) is 1.5 time greater in magnitude than the true wind vector. And still the sail can produce a force that has a positive vector component in the direction of travel. The boat can accelerate or hold it's speed.
The_Metatron wrote:
If the wind is blowing due south at 10 meters per second. There is no trick of physics you can do to make that wind push anything due south at faster than 10 meters per second. Period.
Reality disagrees. Period.
http://en.wikipedia.org/wiki/Sailing_fa ... n_the_wind
Indeed iceboats can make good both upwind and downwind at speeds far greater than the wind.[35][36] And so can sand yachts:
...
the yacht Greenbird was proceeding at about 3 times the speed of the wind on a course about 120 degrees off the true wind.[17] Thus, its speed made good downwind was about 1.5 times the speed of the wind.
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It sailed 20 nautical miles (37 km) downwind in 1 hour 3 minutes, so its velocity made good downwind was about 2.5 times windspeed,
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The polar chart in Figure PS1 of the cited book High Performance Sailing[5] shows that boats that were sailing in 1996 were able to make good downwind at about 1.5 times the speed of the wind.
Wrong, see above.
The_Metatron wrote:you cannot break up vector components of a force in such a way that their vector totals exceed the original force.
I have posted a vector diagram that shows how downwind VMG greater than true wind is possible. So far, you have failed to point out any errors in the diagram.