Re: [Paddlewise] Group Paddling - folders stability

From: John Winters <735769_at_ican.net>
Date: Mon, 12 Apr 1999 17:48:58 -0400
Ralph wrote;
(SNIP)

>
>I would love to and Webster's dictionary (and I am sure all naval
>architecture glossaries of terms do too) but sometimes things get called
>something and the label sticks and we just have to start using the term
>in the corrupted way.  :-)

But that don't make it right. I will go away and pout ;-(


>But I do appreciate that there is a distinction...anything to get away
>from the infamy the term has gotten because of your fellow Canadian.

OH YES.

>
>I want to return to the question of stability of buoyancy aids in
>folding kayaks.  And then I am going to leave it because no one seems to
>be applying any real science here other than general, unspecified
>references to Archimedes.  What I have to say comes from observation,
>which has to count for something.

It does but observation can deceive as well as enlighten otherwise
magicians could never make a living.

(SNIP)

>The kayak wound up right
>side up with the woman having a stunned look on her face.  I am not sure
>how another kayak, a non-buoyancy aided flexible skin one, would behave
>in similar circumstances.

Assuming the same shape and circumstances a hard-shell would probably have
done the same thing. I suspect the standee pushed against the hull creating
a righting moment as he fell similar to what happens in a canoe when a
paddler falls out. Most people fall out of canoes and the canoe ends up
floating away right side up even with another paddler aboard..

(SNIP)
>It didn't.  While the wave
>side of the kayak rose way up and we were well over, something kicked
>in, without any bracing whatsoever by either of us...my wife didn't know
>how to brace and both my hands were on my rudder lifter line.
>Will folding kayaks flip?  Of course they can and do.  But it takes a
>lot, and my observation tells me that the bouyancy aids inside are
>kicking in at some point to some degree enough to say that the
>phenomenon does exist.


Possibly the wave action at the right time or instinctive movements on your
part. I don't know since I didn't observe it first hand but to say that the
air tanks inside a boat affect stability in the unflooded condition
contradicts the laws of Newtonian Physics.

While what you observed certainly did occur, one has to recognise that the
laws of physics do not change just because a boat can fold up. Water is
basically very stupid and cannot tell if a boat is an aircraft carrier or a
kayak. Unlike justice, water really is blind and treats all that float in
it with equality.

To put this kind of thing on a scientific plane I would gladly enter the
offsets of any folder that anyone wishes to send me into my computer and
calculate the stability both in an unflexed rigid and in a flexed mode to
see what happens. I did it today with a "folder " I designed and the
unflexed boat had greater stability.

Keep in mind  that my program can calculate both flooded and intact
stability so we have a lot of flexibility.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/



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Received on Mon Apr 12 1999 - 14:51:47 PDT

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