Re: [Paddlewise] Pro's and Con's of the "Swede Form"

-----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/

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