Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: notesfiles - hp 1.2 08/01/83; site hp-pcd.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!oliveb!hplabs!hp-pcd!daver From: daver@hp-pcd.UUCP (daver) Newsgroups: net.rec.boat Subject: Re: sailboards: *why* heeling is obsolet Message-ID: <15700002@hpcvrd.UUCP> Date: Tue, 13-Aug-85 20:56:00 EDT Article-I.D.: hpcvrd.15700002 Posted: Tue Aug 13 20:56:00 1985 Date-Received: Mon, 19-Aug-85 08:25:17 EDT References: <861@mtuxo.UUCP> Organization: Hewlett-Packard - Corvallis, OR Lines: 25 Nf-ID: #R:mtuxo:-86100:hpcvrd:15700002:000:1519 Nf-From: hpcvrd!daver Aug 13 16:56:00 1985 >Back to basic airfoil theory -- why does a sailboat sail upwind? While the previous responses are reasonably accurate the real reason a sailboat can go upwind is because of the keel, centerboard or daggerboard. When the wind hits a sail at the optimum angle the force vector on the sail is at best perpendicular to the wind. The reason the boat is able to sail closer to the wind than this force is that the combination of the keel/centerboard/ daggerboard with the rudder/skeg produces a resistance to motion perpendicular to the centerline of the boat. If you decompose the force vector on the sail into components parallel to and perpendicular to the centerline of the boat or board and then reduce the component perpendicular to the boat by the resistance force created by the stuff hanging down below the boat, you find that the net resultant force, which propels the boat, can be actually somewhat into the wind. The resistance force created by the keel, etc. is also responsible for a boat heeling, as you need two forces to create a torque (in steady state). On a sailboard the weight of the sailor on the upwind edge of the board compensates for the combination of the downwind force on the board at the mast step and the upwind force at the daggerboard to prevent the board from heeling. Since the distance between the two forces (the lever arm) is much shorter on a sailboard than on a conventional sailboat, there is much less heeling tendency to counteract. Dave Rabinowitz hplabs!hp-pcd!daver