-----Original Message----- From: 735769 <735769_at_ican.net> John Winters wrote <SNIP> >Somewhere I have a report of a study of an >International sailing canoe that showed a considerable increase in >resistance at relatively small leeway angles of about 5 degrees. If I recall >correctly it was something in the order of 40% for a boat with a centerboard >down. I will dig around and see if I can find more somewhere in my stack of >papers. > >Rudders and skegs with good airfoil shapes can help reduce leeway and >weathercocking by providing some lift. Easy to see a rudder reducing weathercocking. Its harder to see how it reduces leeway if it is way back on the stern. I can see a rudder might help reduce leeway a little on a boat that weatherhelms but it would seem to add leeway to a boat with a lee helm (to correct you would swing the stern further downwind). Since your point seems to be that a kayak may have considerable added drag due to the somewhat crablike motion of leeway (at least a sailboat with a centerboard may exhibit this) and that a rudder can reduce the leeway it appears you are implying there will be less drag in a side wind if you have a rudder. I think finding an example from canoes, kayaks or even ships would be more relevant here since most kayaks don't have a large centerboard to confound things. It seems to me that the rudder will create more drag for several reasons. It is adding wetted surface just by being there (Sea Kayaker Magazines 1986 towing tank tests showed 10% more drag at 3 knots--going in a straight line). If the rudder was fixed (like a skeg) the kayak's leeway will mean the rudder/skeg is moving at an angle and therefore sweeping out a wider chunk of water than its thickness (this is probably also the reason the centerboarded sailing canoe might--if you are correct--add so much drag due to 5 degrees of leeway). If the rudder is angled to correct for weatherhelm then it is now sweeping out an even wider swath through the water adding even more drag (if correcting for lee helm the angle would be less than that just due to leeway on a skeg and that should reduce drag). In "Ships in Rough Water" Kent says that the rudder becomes the major retarding force on a merchant ship when it is angled enough to correct for weatherhelm in gale force sidewinds. More drag due to the rudder than all other forms of resistance combined. WOW! Somehow I don't think the rudder reducing leeway a bit has helped much here. More subjectively, the other day I was paddling a kayak that tended to yaw but the center of gravity kept going in the direction it had been going in originally so the kayak kind of skidded sideways at a noticeable angle (maybe 10 to 15 degrees). It seemed to do this without slowing down very much so I don't think there was much added drag due to crabbing to the side a little bit, certainly not anywhere near 40%. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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