Thread View: net.rec.boat
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Started by d.isenberg
Thu, 08 Aug 1985 17:21
sailboards: *why* heeling is obsolete.
Author: d.isenberg
Date: Thu, 08 Aug 1985 17:21
Date: Thu, 08 Aug 1985 17:21
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Back to basic airfoil theory -- why does a sailboat sail upwind? Because a low pressure area develops on the leeward side of the sail (or, conversely, a high develops on the windward side). This pressure difference is also the cause of heeling; not only does it drive the boat *forward* it also sucks it *down to leeward*! Now, suppose that you could take that low pressure to leeward and make it suck your boat up and forward instead of down and forward. You would then be developing lift and forward drive instead of heel and forward drive. THIS IS EXACTLY WHAT A FULLY ARTICULATED RIG BUYS YOU. Definition: a fully articulated rig is hinged on deck in such a way that it can pivot freely 360 degrees in the horizontal dimensions and 180 in the vertical. In other words, the mast, boom and sail can pivot freely, attached at one point only, as long as they remain at deck level or above. So, here's how you use it. When the wind starts to blow on a conventional rig, it heels, thus reducing the sail area presented to the wind. When the wind blows on an articulated rig, the sailor reduces the sail area presented to the wind by inclining the rig *to windward*, and the result is lift. On a sailboard, the experience is absolutely thrilling: you are leaning back hanging all your weight on the sail, i.e. taking all your weight off the board, and the board, which suddenly displaces say 50 pounds (instead of the ~200 pounds it had with your full weight on it) why -- thaat board TAKES OFF !!. And there you are flying along over the water with all your weight hung in the air spilling just enough wind to keep a big toe from each foot on the board to steer it. So THAT'S why I say that the fully articulated rig makes heeling obsolete (just like this technology here makes paper obsolete). I have seen one of Dick Newick's big trimarans with a huge hairy universal joint at the bottom of the mast (and big hydraulic cylinders on each of the stays and shrouds for radical adjustments of their length). And I did hear that the first monohull to finish the last OSTAR also had a fully articulated rig of some kind. I believe that the fully articulated rig is the most important sailing breakthrough since the development of the fore 'n' aft rig. Will we see f.a.r.'s in Perth? Maybe after they let multihulls race :-). If you need to be convinced, try board sailing. If you thought sailing a conventional rig was fun . . . . . David Isenberg ihnp4!mtuxo!isen 201-576-6386
Re: sailboards: *why* heeling is obsolet
Author: daver
Date: Wed, 14 Aug 1985 00:56
Date: Wed, 14 Aug 1985 00:56
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>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
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