Subject: Re: [baidarka] Lift and Drag
From: James Mitchell (baidarka@earthlink.net)
Date: Tue Oct 26 2004 - 16:40:03 EDT
Just came back from Juneau, paddling on Auke Lake around the corner
from the Mendenhall Glacier. Was going to paddle the glacier lake, but
it was frozen over already! Sunny and cold, a beautiful week in
Southeast Alaska. I paddled two older boats of mine, Otter (single
17'x22") and Chinook (double, 20.5'x28"), both still a treat. And now I
have a kayak storage shed in Juneau.
I see where you get your description of lift now. I understand the two
45 degree lift vectors you are describing. I still don't believe that
they are generating anywhere near the force that is coming from the
resistance of the paddle's surface area to the water, but that
discussion should wait for some instrumentation and lots more theory. I
agree, and have always agreed, that we don't need to understand any of
this theory in order to build good paddles, and I salute anyone who is
really building and really using their own paddles. As we say in warmer
waters, "Gambatte kudasai!
On Oct 13, 2004, at 11:31 AM, Peter Chopelas wrote:
> From: "James Mitchell" <baidarka@earthlink.net>
>
>
>> Peter, let's see if I understand you correctly. You are saying that
>> the
>> flow from the ridge outboard to the edge is generating significant
>> lift? If that is what you are claiming, you are free to claim it but I
>> still disagree.
>
> No you misunderstood, perhaps I was not clear. The flow goes from the
> ridge
> to the edge, and then wraps around the edge generating the vortex on
> the
> backside (the side opposite the ridge). The two vortexes formed this
> way
> are curling in towards each other, pulling the fluid flow around the
> back of
> the blade in a half arc on each side. This acceleration of the fluid
> around
> these two vortexes is what generates the lift in the forward direction
> (on
> the side away from the ridge side). This is known as vortex lift, and
> if
> you watch turbid or water with bubbles in it you can see how the "far
> field"
> flow is curved around the blade (that is the flow not right against the
> paddle surface). There are actually two lift vectors, one from each
> vortex,
> that are at about 45 degrees to eachother (I suspect), both forward.
> Then
> net effect is a forward thrust. Note that if the two vortexes are not
> of
> equal size the blade will pull one way, and then the other and you get
> flutter. This is why the ridge is important.
>
>> I do agree that a Greenland paddle held as you describe is generating
>> lift, in much the same way as a propeller: a rapid sweeping motion
>> with
>> the paddle at a slight downward angle. I find this stroke interesting,
>> and one of my kayaking friends in Japan uses this stroke successfully
>> for long distances. It does not fit my paddling style well, although I
>> have used it as a break during long paddles. I hope you agree with me
>> that an Aleut paddle is not well suited for this stroke.
>
> exactly correct.
>
>
>
>> The low-speed
>> foil shape of the traditional Greenland paddle is well suited for this
>> stroke, but not as well suited for the typical "resistance-based" (for
>> lack of a better term) stroke that we do with the Aleut paddle.
>
>
>> I design my paddles for smooth power over long distances. I optimize
>> them for ease of paddling, for greatest ease on the paddler's muscles
>> and joints, for the greatest efficiency in a relaxing long distance
>> touring stroke. To my knowledge, everyone who has paddled with one of
>> my paddles agrees that the paddle accomplishes this goal. In
>> accomplishing this design, I have started with the best traditional
>> design knowledge I could find, and continued to optimize it for power
>> and smoothness -- and for weight and "feel". These discussions are
>> interesting to the extent that they contribute to the design.
>
> And you have done a good job of it too. There is no reason you need
> to know
> a lot of technical stuff to experiment with paddle shapes and find what
> feels good and what works good. That does not mean that you have a
> clear
> understanding of how or why it happens, nor do you need to know to
> make a
> paddle that you like.
>
>>
>> Given that you have a different understanding of the physics involved
>> in accomplishing my goal, please tell us all: what have you learned
>> from your study? How are your paddles shaped? What experience do you
>> have in paddling your ideas? How do you apply what you have learned?
>
> This understanding has made me realize why high aspect ratio native
> paddles
> are better for long distance cruising, it has helped me develop some
> of the
> finer details of the paddle shape (which are not obvious from printed
> drawings or pictures) and it has helped me fine tune my stroke
> mechanics and
> rolling technique. I have also developed a paddle shape of a
> Greenland type
> paddle that tapers toward the tip (rather than the more common reveres
> taper) that I really like. After I had made it I have learned that
> this
> exact shape is illustrated in Peterson's "Contributions..." book in the
> chapter on paddles. How about that?
>
> Peter
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>
James Mitchell
Email: baidarka@earthlink.net
US Mobile Phone: 425-273-0884
15917 Waynita Way NE, E103
Bothell WA 98011 USA
-
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