Subject: RE: [baidarka] Superiority of Native paddles
From: Peter A. Chopelas (pac@premier1.net)
Date: Thu Jun 28 2001 - 00:24:19 EDT
On Wednesday, June 27, 2001 2:16 PM, Michael Daly
[SMTP:michaeldaly@home.com] wrote:
>
> Peter, both here and on Paddlewise you have adopted the same three
> techniques in dealing with others who question your hypotheses:
I have used no such "techniques". None of these accusations are true, I do
not know what you are talking about. See my comments below:
>
> 1 - ridicule their comments (as you've done here)
I ridiculed no one, I only made statements of fact. If objectives
statements come across as ridicule I apologize for that was not my intent.
Where is there any ridicule in my posting, go find it and show me? Can
you tell me how might a simple statement of fact not be construed as
ridicule?
> 2 - tell them they're wrong and offer nothing.
I made explanations for each of my statements, if you consider these
efforts "nothing" then I do not know what else I can give you. What is it
you want? Detailed lessons on fluid mechanics? Three dimensional partial
differential equations combined with finite element analysis so we can
derive the Navier-Stokes equations for you? Not practical here.
I think the equations are valid, as least for some conditions (I am not
willing claim they are always valid, I know likely they are not), and no
one as yet has convinced me otherwise at least for a cruising stroke. If
you can not accept them as valid fine, but I can not "prove" to you they
are valid any less than you can prove to someone that Newton's equations of
motion are valid with out going out and doing a lot of controlled tests.
You either have to run the tests yourself, or just accept them as valid.
One of the real problems I think (with all due respect, and not written
with ridicule or prejudges at all) is that fluid mechanics is very
complicated and not intuitive at all. The reasons the reactions follow
certain mathematical relationships is not easily communicated with simple
examples or a few descriptions.
Consider the first controllable glider was only invented about 120 years
ago, yet all of the materials that it was make from was available in the
bronze age. Boats and paddles have been around a long time of course but
even crude ones work, the traditional kayak (and paddle) is a remarkably
advanced design compared to most boats. But, unlike a boat, you need a
certain threshold of understanding before you can make even a simple
aircraft (like a hang glider) fly at all. Now of course many people build
homebuilt, hang gliders and ultralight aircraft in their garages, all
possible perhaps 1000 years ago if only the understanding of how they work
was available (including internal combustion engines). Most of the people
that build homebuilt aircraft could not explain to you the theory of why
their aircraft works, they just know if you follow certain principals it
does (I know a number of these builders too).
Unlike the aircraft however, the basic design of the kayak has not really
been improved upon much (except for modern materials), compare that to
aircraft design in just the last 100 years! I'm sure the native kayak
builders understood none of the theory or equations, but they could observe
what works well, and what does not. So even with the theory to understand
WHY it works, there in not much improvement we can make to it, or the
paddle.
> 3 - call them ignorant morons.
I did not call anyone names, nor did I imply this at all. Go back through
the archives and find anything that I wrote that calls anyone names at all,
or even implies that I did so. You are making unfair and unfounded
accusations.
<snip>
>
> 4) AR = span / mean chord. --- which is independent of shape.
>
> You should have known that, if you were the expert you claim to be.
>
I know that, and always knew that. How is what I wrote showing I did not
know this? It was the other person that claimed my definition of AR was
incorrect. Using the "mean chord" is accurate but it is not easily
determined on an irregular plan form, the more universal definision is the
one I gave, which is exactly the same as using the "mean chord". But how
do you determine the mean chord on an irregular shape?
>
> And also the horsepower estimates you've been using are way off.
> An elite paddler can produce at most about 0.3 hp for an hour. An
> elite cyclist, about 0.5 hp. An average paddler can produce only
> about 0.1 hp; some less. If you plug the numbers into those from
> Matt Broze's drag calculations and hp calcs for typical kayaks,
> you get efficiencies on the order of 25% and up.
>
I do not know where you got these numbers, they a bit high in my
experience, in 1982 I was one of a number of engineers who developed the
bicycles used by the US cycling teams in the 1984 Olympics. And I was
involved with directly measuring and analyzing the data from actual tests
of power in-put and power out-put on human dynamometers.
A third of an HP is about right for an athlete for sustained output, with
peak bursts at .5 and higher. A healthy person in really good shape (but
not an Olympic athlete) could sustain about .25 HP. The average 'week-end
warrior' (including me) would have a good time doing about half of that.
The power output is directly proportional to the cross sectional area of
the of the muscles being used, the arm muscles are typically about half the
X-section of the thigh muscles, so power out put should be in the order of
0.06 hp for an average paddler.
This is oversimplifying the picture because you use more than just your arm
muscles when paddling, and unlike a peddle crank on a bike I am not sure
how you could accurately measure total power output on a machine with the
paddling motion.
Though I think you are being overly picky here, I made no claim to accuracy
but was demonstrating that an order of magnitude improvement might be
possible. Even using your own number of 25 percent for just the paddle
(power-in at the handle vs. useful power out) shows there is lots of
improvement to be made. A typical light aircraft propeller is about 75
percent efficient, and I think I remember seeing boat props in the 60
percent range (others might know more about this). So even if you can get
a paddle to "only" 50 percent it would be a huge improvement. Of course,
maybe not.
We will not know without going out and testing it, as good a reason as any
to make a new paddle and go paddling as far as I am concerned, even if we
do not learn anything. ;-)
Peter
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