How does a boat sail close hauled?

Question

Could I get an explanation how power goes to the sails if close hauled wind is theoretically blowing it backwards? Thanks

Answer 1

I've sailed for 40 years and 30,000 miles and there are days that I don't understand it at all....but, combining two of the answers before me......

your sails when going upwind have a curved shape to them.  An airplane wing does too. When the planes engines thrust the plane forward the airflow over the wing produces and upward force called lift. On a plane that's straight up 90 degrees to the wing's top surface. ( more or less)  ; on a sail that's also at 90 degrees to the top, curved side of the sail

Now, lets do a vector drawing. Imagine a top down view of the sail, sheeted in tight to the center line of the boat. That lifting force at right angles to the surface of the sail gives a thrust, or arrow that is going forward and at a slight angle to the center line of the boat; if you were looking at a clock face of a boat on starboard tack, with the bow pointed at 9 o'clock and the wind from 11,  that arrow would point to, say, 8 o'clock.

Now, you have the underwater shape of the hull, either a keel or a centerboard exerting force to keep you from slipping sideways. On the clock face boat above, that force would be an arrow perpendicular and up to the boats course. So, go to the end of the 8 o'clock arrow, draw another, short arrow pointing at 12 o'clock. You now have forward force form th e sail and upwind force form the keel. Draw a line form the center of the clock to the top of the short arrow out there at the end of the long arrow....and that is the resultant course the boat sails.

Answer 2

Sails take the shape of an airplane wing causing a low pressure on the forward side.  The concept of sailing is easier when you realize that the sails are sucked by that low pressure.

Answer 3

Physics, my boy...physics.  Look up Sir Isaac Newtons theories and that of Bernouli.

The sails are a foil as an airplane wing. Thus you have lift(hopefully) which results in motion. A sailboats keel contributes anti-roll stability  by virtue of its weight to counteract the pressure of the wind in the sails. The length of the keel or keel fin/strut provides some directional stability in combination with the rudder.  Sails are not flat...some are flatter than others...but be assured they are all curved. Because of this they must be full and to be full you cannot sail directly into the wind...ie: Head to Wind or "In Irons"  

As a racer, I can approach the line and find my slot then sit head to wind and indeed slide backwards...the art is to be able to control your boat and have the bow break on the desired side to power up and take off. This was seen in the last Americas Cup match and is pretty interesting to watch.

Answer 4

It does not blow it backwards.  It transfers energy to the sail, but the sail pushes laterally into the boat.  Since the mast is forward of the center of the mass of the boat, it actually pushes the front of the boat a bit downwind.  This downwind motion gives some forward thrust to the boat, which quickly adds up.  This gives enough speed for the helmsman to try to bring the bow back onto the heading.

There is a centerboard, a blade sticking out of the keel, which helps to convert the lateral energy to forward energy, and helps to limit or eliminate lateral drift.

Answer 5

Close Hauling is a point where the boat is almost, but not quite sailing INTO the wind.  If you were to turn anymore into the wind your sails would begin to luff.  You are actually sailing diagnolly to the wind even if it looks like you aren't.  The wind fills the sail driving it forward.  You don't sail very fast when close hauling and you must be on constant alert to changes and gusts in the wind.  If the wind changes even one or two degrees, you find yourself in the No-Go Zone and at a standstill with your sails flapping every which way.  

Good luck.  It takes an experienced sailor to make it work well,