sam257 Posted February 22, 2007 Report Share Posted February 22, 2007 hey everyone, I was just wondering if anyone could explain to me how a sail works ? cheers Link to comment Share on other sites More sharing options...
Emmessee Posted February 22, 2007 Report Share Posted February 22, 2007 It is fairly simple to explain how a sailboat sails when going downwind. (When the wind is behind you.) You simply let the sails out as far as they will go and the wind pushes on them and the boats hull follows along. However, when the wind is coming from the side there are some special physics at work. The force that the wind transfers to the sails actually makes a boat move forward for much the same reason a plane flies. If you were to look down on a sailboat from a helicopter you would see what looks like an airplane's wing, except standing on end. The air moving across the sails, like air moving across an airplane wing, creates a force called lift. A small amount of this force aims aft and actually pushes the boat forward and some of the force is lost due to friction as it moves over the sail. However, most of the force is sideways which tends to make the boat move sideways away from the wind. The keel or centerboard keeps the boat from being pushed sideways by the wind. The resistance from the hull and the keel translate the lifting force to forward motion. If you did not have a keel or centerboard the boat would simply move sideways away from the wind. However, with a well-shaped keel the boat will sail mainly forward while sliding slightly to leeward (away from the direction the wind is blowing). [This message has been edited by Emmessee (edited 22 February 2007).] Link to comment Share on other sites More sharing options...
HooD Posted February 22, 2007 Report Share Posted February 22, 2007 http://en.wikipedia.org/wiki/Sails wikipedia is just a great resource. Link to comment Share on other sites More sharing options...
PP Posted February 25, 2007 Report Share Posted February 25, 2007 I believe the 'lift' pulling the boat forward from the leward side of the sail is actually more than the push obtained from the wind on the windward side of the sail. The headsail actually sets up this lift for the main sail and is called the slot effect, both sails combine their lift for a much greater effect than could be achieved if the headsail was much further forward. Link to comment Share on other sites More sharing options...
Norman Jones Posted October 19, 2007 Report Share Posted October 19, 2007 Originally posted by Emmessee: It is fairly simple to explain how a sailboat sails when going downwind. (When the wind is behind you.) You simply let the sails out as far as they will go and the wind pushes on them and the boats hull follows along. However, when the wind is coming from the side there are some special physics at work. The force that the wind transfers to the sails actually makes a boat move forward for much the same reason a plane flies. If you were to look down on a sailboat from a helicopter you would see what looks like an airplane's wing, except standing on end. The air moving across the sails, like air moving across an airplane wing, creates a force called lift. A small amount of this force aims aft and actually pushes the boat forward and some of the force is lost due to friction as it moves over the sail. However, most of the force is sideways which tends to make the boat move sideways away from the wind. The keel or centerboard keeps the boat from being pushed sideways by the wind. The resistance from the hull and the keel translate the lifting force to forward motion. If you did not have a keel or centerboard the boat would simply move sideways away from the wind. However, with a well-shaped keel the boat will sail mainly forward while sliding slightly to leeward (away from the direction the wind is blowing). [This message has been edited by Emmessee (edited 22 February 2007).] Link to comment Share on other sites More sharing options...
Norman Jones Posted October 19, 2007 Report Share Posted October 19, 2007 Have you still got a tri-fly ? Link to comment Share on other sites More sharing options...
catsailor.net Posted October 23, 2007 Report Share Posted October 23, 2007 If I knew - I would win Link to comment Share on other sites More sharing options...
Leapin Leroy Posted October 23, 2007 Report Share Posted October 23, 2007 Sam, Air molecules moving over the sail have to "split" when they hit the front of any sail or mast (figuratively & literally speaking). The ones flowing over the leeward side have to travel faster than the ones travelling over the windward side to keep up, otherwise you would end up with a pure vacuum as found in space.... This creates an area of LOW pressure... As HIGH pressure wants to fill the "void" created by the low, you have the phenomenon called lift, the sail wants to fall over to leeward... Taadaa.... Ummm, angle of attack has a fairly major influence on the whole of this process.... Daaadum... The hydrodynamic forces and resistances created by the hull, keel/centreboard, and rudder shapes all help to translate the lift into VECTOR forces that result in (hopefully) forward motion... Boom Tishhh.... There are a multitude of research materials available and the are all very interesting to read. Some can be incredibly dry (read boring), but most very interesting, as Matt said, think of a (glider/hang glider) wing turned on it's side and away you go... It's also one of the fundamental reasons why it's important to keep the tell-tales flowing over the sail at all "angles of attack" (both up wind and down)... Good luck & hope this helps, Regards, Leroy (Added later)... Drag is also a byproduct of lift and aerofoil shape, thats the bad stuff... [This message has been edited by Leapin Leroy (edited 23 October 2007).] Link to comment Share on other sites More sharing options...
tgh Posted January 2, 2008 Report Share Posted January 2, 2008 http://www.northsailsod.com/articles/article6-1.html I was tempted to contribute at the time .. but my aerodynamics were about as rusty as my sailing smarts.. anyway... this is a good primer about sails... if the original poster still wants to know .. Link to comment Share on other sites More sharing options...
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