-----Original Message----- From: Philip Torrens <skerries_at_hotmail.com> >It was suggested that using a rudder is an easier way to "adjust the trim" >of a kayak than by judicious packing of cargo. My boat has a rudder, and I >still am careful to pack it balanced fore and aft. Here's why: > >I prefer to paddle without the rudder as much as possible, both to keep my >skills up and because the rudder creates drag. Yes, Sea Kayaker magazine got 10% more drag at 3 knots due to a deep draft/flat blade/high aspect ratio rudder being in the water and free to trail straight back. They felt that that much extra drag seemed too high and ran the test again to check the results. The results were the same (10% more) on the second run. > >Even when I am using the rudder, a well balanced boat requires less radical >rudder angles for course correction. The harder you have to put the rudder >over, the more "stall" (read "drag") you may create. A very good point! The area that the angled rudder sweeps out to correct for weatherhelm adds as much drag as a flat stick of that area being dragged perpendicular to the flow. If you must angle the rudder more to compensate for the extra weatherhelm you create by how you load the kayak that "virtual" vertical flat stick you are "virtually" dragging will get wider. This is all added on top of the drag created by the rudder itself (that wouldn't be there if you didn't need to use it). unfortunately there is no free lunch and trim change has costs as well. Joan Spinner mentioned that she felt there was more drag when she added weight to the stern. I'm not sure there would be enough extra drag to be that obvious but a hull that is out of trim to the stern will add more drag than one that is equally out of trim (down) at the bow. Level trim should be the fastest. I don't know how big this "out of trim" effect is at cruising speed (and have asked John Winters if he had any data on this several months ago because some of the kayaks Sea Kayaker reviews do not sit at level trim and I felt our drag calculations should reflect this (if we could find any applicable experimental data to use to quantify the effect). Adding extra weight to create the trim change will also have costs in (slightly) increasing drag and ( perhaps more significantly) slowing accelleration. Many paddlers use accelleration to (erroneously) judge a kayaks speed. Joan may have used accelleration to judge speed and her lightweight friend didn't. I have run top speed tests with the original Mariner at different trim positions (easy to do when you can move the seat 18 inches). Bow down trim added about 1/2 to 1% to my sprint times. With the seat 9" behind trim I was about 4% slower in an all out sprint than when level. With my 180 pound body shifted to the extremes of seat adjustment we measured a 4" difference in water level at the stern with that boat. > >Murphy's (Posiden's?) Law dictates that a rudder cable will break or a >sliding footpeg jam at the most inconvenient moment (the latter has happened >to me). You're going to have to pull the rudder out of the water and steer >with paddle strokes then; why not make it easy on yourself? > Maybe you should have a back up rudder. 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/ ***************************************************************************Received on Fri Sep 03 1999 - 14:48:11 PDT
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