-----Original Message----- From: John Winters <735769_at_ican.net> To: paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net> Date: Friday, April 30, 1999 6:43 AM Subject: Re: [Paddlewise] (un)Feathered paddles in surf >Matt wrote; >>True, but I doubt way out at the paddle blade (at least when it is at the >>angle most effected by the wind) ones body has much effect. > John answered: >According to my information effect extends up to 2.5 times the chord width >of the object in the flow. In this case probably 5 feet or so for a human >body. Mind it diminishes with distance. My (recent) research into aerodynamic texts indicates that some small effect may happen even further out than that, but even if the wind is deflected until it is hitting the paddle at an angle of up to 25 degrees to perpendicular the drag will be almost the same as if it were perpendicular so it will hardly matter way out at he paddle blade (where the wind is only deflected a few degrees or less by the paddler). This diversion of flow around the paddler (that causes the "safe lee" and "hopeless" positions in sailboat racing) if it occurs to any significant degree would only mean that the paddlers unfeathered blade would be perpendicular to the flow a little later in the stroke. >(SNIP) >>Since the paddle is most effected when it is perpendicular to >>the wind > >Not necessarily so unless you mean that the drag reaches its maximum. The >effect of the adjacent body increases with proximity as well as orientation >to the flow. Maximum drag is what I meant by most effected. Not much changes, drag wise, if the flow is withing 25 degrees to perpendicular, so the unfeathered paddle would have to be very close to the body to get much benefit from this effect. > >>and since one paddles with the paddle out in front of the body, if >>the flow is altered by the body way out to the paddle blades it is more >>likely to be deflected at the paddle blade when the wind is from behind >the >>body and the paddle is therefore further downwind. Since an unfeathered >>paddle is also deflecting the wind it is possible (especially near the end >>of a stroke) that the upper blade (angled forward like a scoop) is >>deflecting some wind into the paddlers wind catching body to some extent >and >>this might further slow the paddler down. > >Interfering bodies do not necessarily have additive drag but influence each >other. This provides the explanantion for why solo paddlers have so much >less efficiency than tandem paddlers when paddling against the wind. This may be true in special cases, but my personal experience racing has been that when we turn into the wind is when I (in my single) can finally catch the double that had been previously out of reach. (Then I use this effect--hiding from the wind--behind them and their wake to "draft" them and get a rest before passing). Of course, any angle much off of directly into the wind would be a disadvantage to the bigger frontal area of a double with twice the number of paddlers sticking up into the airflow. That could be the reason I caught up or maybe they were all just using unfeathered paddles into the wind and I wasn't. >The >aft paddlers creates less drag because he lies in the forward paddler's >turbulent wake. The same applies to paddles and paddler. Thus the drag of >the paddle can reduce the drag on the paddler producing less net drag than >if the two bodies get treated individually. In the case of the untwisted >blade, the total drag on the system could be quite similar to that of the >twisted blade. If anyone out there has a copy of Horner's Fluid Dynamics >they can check this out as I recall there being some discussion of the >various research papers on this topic. My own copy is out on loan so I will >have to wait a week or two to check it out myself. > If you held the paddle blade directly in front of yourself that would be true but it would be hard to paddle much that way (but a near vertical stroke might provide a small benefit here). Matt Broze www.marinerkayaks.com > > > >*************************************************************************** >PaddleWise Paddling Mailing List >Submissions: paddlewise_at_lists.intelenet.net >Subscriptions: paddlewise-request_at_lists.intelenet.net >Website: http://www.gasp-seakayak.net/paddlewise/ >*************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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