-----Original Message----- From: Nick Schade <schade_at_guillemot-kayaks.com> To: PaddleWise_at_lists.intelenet.net <PaddleWise_at_lists.intelenet.net> Date: June 8, 1999 11:50 AM Subject: Re: [Paddlewise] Pro's and Con's of the "Swede Form" (Large SNIP) > >Ignoring a factor because it is too small to be significant and ignoring it >because you don't think it exists are two very different propositions. To >say that a submarine 3 diameters below the surface experiences no surface >drag is different from saying a submarine 3 diameters below the surface >experiences negligable surface drag. I applaud Nick's passion for absolute accuracy on this although I think he got the point of Gilmer's statement which, of course, was the point, wasn't it? >What happens when two submarines cruise next to each other at 3 diameters >below the surface.? How close do they have to be before they produce a >non-negligable surface drag. If your knowledge says "3 diameters -> surface >drag = 0" then you have no reason to suspect that there would be any >surface drag until they touched. I don't see this? Just because no measureable interference drag exists at three diameters (actually the separation would have to be six diameters for two boats cruising side by side but I think I understand what you mean) do you conclude none will exist until they touch? Why say three diameters if measureable drag didn't start thereabouts? >Where if your knowledge says "3 diameters >-> surface drag >0" you might choose to investigate further. Or what if the >sea floor is 4 diameters down? The interaction of 2 or more undetectable >reactions may be detectable, and may even be significant. It does not help >your knowledge to dismiss undetectable reactions as non-existant. I suppose has similarities to the sheer on a sea kayak. The precise location may be difficult to determine for those who don't recognise or concede that at some point the deck becomes the hull sides but that doesn't mean the sheer doesn't exist. :-) (A little in joke) >Rules of thumb only work as long as they are being used within the scope of >their assumptions. If you follow a rule of thumb without knowing the the >science behind the assumptions and the limitations of those assumption, you >only have enough knowledge to be dangerous. If you know the science behind >the rules, you have enough knowledge to safely make your own assumptions >and you can detect when the rules no longer apply. Do you think Gilmer knows (Knew) his stuff? >Saying "Waves cause drag" is a good enough rule of thumb in many cases >because waves are a symptom of drag and if the waves disappear so has the >drag. But it could lead to the conclusion that paddling in an environment >where waves can not exist would eliminate the drag. This is not the case. >What you really want is to eliminate imparting any net velocity to the >water and the waves will disappear as a side effect. Hear! Hear! Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
At 6:42 AM -0400 6/9/99, John Winters wrote: >>What happens when two submarines cruise next to each other at 3 diameters >>below the surface.? How close do they have to be before they produce a >>non-negligable surface drag. If your knowledge says "3 diameters -> >surface >>drag = 0" then you have no reason to suspect that there would be any >>surface drag until they touched. > >I don't see this? Just because no measureable interference drag exists at >three diameters (actually the separation would have to be six diameters for >two boats cruising side by side but I think I understand what you mean) do >you conclude none will exist until they touch? Why say three diameters if >measureable drag didn't start thereabouts? Right, I'm just blindly following the rule of thumb and don't know any better. It is only because you know more about the physics that you realize that there is an interaction between the boats that changes the rules. > >>Rules of thumb only work as long as they are being used within the scope >of >>their assumptions. If you follow a rule of thumb without knowing the the >>science behind the assumptions and the limitations of those assumption, >you >>only have enough knowledge to be dangerous. If you know the science behind >>the rules, you have enough knowledge to safely make your own assumptions >>and you can detect when the rules no longer apply. > >Do you think Gilmer knows (Knew) his stuff? I'm sure Gilmer did know his stuff, so he knew when not to use his rule of thumb. Maybe I don't and would like to apply it in all conditions. I also would like to use the following rules: Longer boats are faster, wider boats are more stable, boats with less rocker track better, boats with higher sheers are more stable , more stable boats are safer and wider paddles are more efficient. Why can't I use these all the time? Everything else being equal any one of these rules works. They are even useful when things are not being held equal. But they are not universal rules that can be applied indiscriminantly. You need knowledge beyond the rules of thumb to be able to apply them correctly. Nick Nick Schade Guillemot Kayaks 10 Ash Swamp Rd Glastonbury, CT 06033 (860) 659-8847 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** 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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