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Author Topic: Wind speed and sailing.  (Read 4420 times)

paul.fr

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Wind speed and sailing.
« on: 24/01/2008 14:52:44 »
If the wind was blowing at 30 knots and i am in a sailing boat, can i travel faster than the wind is blowing?


 

another_someone

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Wind speed and sailing.
« Reply #1 on: 24/01/2008 18:40:58 »
Simple answer - no (at least, the exception might be if you have a 40 knot current pulling you along).
 

Offline Bored chemist

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Wind speed and sailing.
« Reply #2 on: 24/01/2008 19:30:07 »
"Simple answer - no "
Correct answer - yes.
http://www.physclips.unsw.edu.au/jw/sailing.html
 

another_someone

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Wind speed and sailing.
« Reply #3 on: 24/01/2008 19:56:02 »
"Simple answer - no "
Correct answer - yes.
http://www.physclips.unsw.edu.au/jw/sailing.html

OK - my mistake again - I was thinking in historic contexts where the speed of the wind was a limiting factor in transportation, but ofcourse they did not use modern sails (mostly the older boats would be square riggers, and even later when fore aft rigging was used, the sails were generally heavier and not as aerodynamic as modern sails, and tack as well as modern boats - I had not thought about high efficiency tacking).
 

Offline Soul Surfer

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Wind speed and sailing.
« Reply #4 on: 25/01/2008 11:58:46 »
It is unlikely that you could sail much faster than a 30 knot wind in a sailing boat because that's pretty close to the maximum speed that most sailboats can go but you might be able to sail faster than a 10knot wind because assume you are in a boat with a good keel and low resistance in the water and are sailing at 45 degrees to the wind.  The fastest you can go is at the speed of the wind downwind but as you are sailing across the wind you are going faster. For 45 degrees this is root 2 or 1.414 times faster.  As you get nearer and nearer to sailing at right angles to the wind this can in theory get very fast but the practical limit is around twice as fast as the wind.
 

lyner

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Wind speed and sailing.
« Reply #5 on: 28/01/2008 16:28:34 »
The design speed for a 25ft boat is about 6.5 knot if it is sailing in 'displacement mode'.  This is about as fast as a normal yacht will ever go, however hard the wind blows; the bow rides up and the stern sits down, as the bow and stern waves coincide and you are effectively sailing uphill after that speed. (Rowing Eights are very long to give them a high design speed). Not many boats with keels will plane but lightweight craft like windsurfers can go much faster when they get up on a plane - the boat just skids over the surface and is kept up by more than  static upthrust..
The fastest water-sailing speed was just short of 50 knot  but, with land sailing, the frictional forces are much less and this link shows some impressive figures (100mph+ in 35mph winds).
http://www.nalsa.org/speed%20record.htm
That demonstrates just how much faster than the wind you can go if you get clever with vectors.
 

The Naked Scientists Forum

Wind speed and sailing.
« Reply #5 on: 28/01/2008 16:28:34 »

 

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