The Physics of Sailing

1. The Physics of Sailing Ashley Conklin

2. Basic Parts of a Sailboat • Mainsail- catches wind • Jib- helps with turning the boat and also catches some wind • Mast- holds up sail • Boom- keeps mainsail stationary and helps to keep constant sail trim • Rudder- provides a way to steer the boat • Keel (fixed) or centerboard (moveable)- stabilizes boat and also uses water pressure to propel the boat forward

3. Is That REALLY Necessary? • Sails… obviously. Otherwise you would be rowing. • Centerboard… yes! The water pressure pushes in the opposite direction of the wind on the centerboard. These two forces combined make the sailboat go forward. • Rudder… yes and no. While it is possible to steer without a rudder (you can use a paddle or use your weight and sail trim) it is annoying and rather difficult.

4. General Rules for Sailing Sit on the opposite side of the sail with your body facing the sail and your eyes focused on the water in front of the boat. Select a point in the distance and constantly aim for it using the rudder. Pull in your sail so that it is catching the most amount of wind as it can. Have your crew pull in the jib in the same manner. Watch for other boats and obstacles

5. Tacking (turning the boat through “irons” or through the wind) Make sure you have enough velocity Point tiller away from sail- but not so far as to be flat against the back of the boat Pull in sail and switch to opposite side of boat If necessary, shift weight to the leeward side of the boat and backwind jib Jibing (turning the boat through downwind point of sail) Point tiller toward the sail Pull in sail or hold onto boom to control boat speed and weight management Let sail back out once it switches sides Turning the Boat Around

6. How the Sails Work • Bernoulli’s Principle • Air travels faster on the windward side of the sail because the sails curve out and therefore there is a smaller distance to travel. • The opposite is true for the leeward side, and the air pressure is lower on this side. • If the sails are kept too loose, they will flap back and forth or “luff” and not catch air, and if they are too tight, the air will bounce off the sail as if it were a brick wall. http://www.yesmag.bc.ca/focus/flight/flight_science.html

7. Points of Sail • Upwind (Irons) • Sails flap, moving backwards • Close Haul • Sails in as tight as possible • Close Reach • Sails at about a 30 degree angle to irons position • Beam Reach • Sails in between all the way out and irons • Broad Reach • Sails almost all the way out • Running (or sailing downwind) • Sails all the way out

8. Sailing upwind is a bit more difficult because you will move backwards if you point your boat into the wind To sail to a point upwind, you must point your boat as close as it will go upwind and tack back and forth until you reach your destination Sailing Upwind wind

9. Sailing downwind is not as difficult as sailing upwind, but it is slightly different than other points of sail. Raising Centerboard Butterflying jib Mainsail can go on either side Pay attention to steering so that you do not jibe accidentally Spinnaker can be flown Sailing Downwind spinnaker

10. Racing • Most sail racing courses have 3 buoys that must be rounded, plus a combination starting and finishing line. • Boats are allowed to start on a whistle (there are warnings beforehand) • In a port triangle course, all boats must round the upwind buoy, followed by the jibe mark, the downwind buoy and then finish through the starting/finishing line • An Olympic course uses the same setup, but instead of finishing immediately after the downwind mark, each boat must then go back and round the upwind mark again, the downwind mark again and finish going upwind.

11. Olympic Port Triangle

12. Resources • http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/josh_palmer/basic.html • Pictures from: • www.wohelo.com/pictures.htm • www.sgcworld.com/faq/faqcoupler.html#10 • http://www.yesmag.bc.ca/focus/flight/flight_science.html