Message-Id: <199704211240.IAA18062@onlink4.onlink.net>
From: "John Winters" <jwinters@onlink.net>
To: <baidarka@lists.intelenet.net>
Subject: Re: bow piece
Date: Mon, 21 Apr 1997 07:58:59 -0400
Lew wrote;
(SNIP)
>
> I wasn't going to read boat rise but am going to collect data from a
> tension load cell (designing a "S" cell for this). This will give me
> some idea if it is humanly possible to paddle the sample kayak at towed
> speeds. Along with this I intend to try correlating the better tow
> results with paddling tests in the same water. I will attempt to do
> this by measuring boat speed, yaw, maybe angle to water and paddle loads
> (paddle loads are loaded with complexities). I have some of the
> equipment to do this already.
I have examined paddle load measurements and they are probably not worth
the effort. The load could be very high yet be very inefficient for
propelling the boat. For instance, a brace could have a very high load yet
would get you nowhere. The measurement of CG rise would be the only valid
measurement to see if planing were occurring since light slender bodies
don't "jump" up on a plane like the typical powerboat. It is often assumed
that it is speed that defines planing (Skene's Elements of Yacht Design for
instance) but it is fairly obvious that it doesn't. For instance, Taylor
tank tested ships at Speed/length ratios above 2.0 (Froude number 0.60)
with no rise of the CG and no planing and destroyer escorts regularly
operate in this speed range. Seeing one of those big ships plane would be a
real treat.
> I am in the process of putting together a rather detailed technical test
> plan and cost estimate. I would be honored if you and Bill Low would
> critique it for me. Both George and Chris Cunningham are interested as
> well. Most of the equipment design and fabrication I can do myself.
> The plan will include a number of boat configurations. Do you know if
> offset measurements exist for all known 18th century Baidarka examples?
> What percentage?
Not sure if offsets exist for all known 18th century baidarkas. I have been
digitizing those that have been published Brand, Zimmerly, Adney/Chappelle,
etc.) as part of a paper for Eugene Arima's next volume of "Contributions
to Kayak Studies" but it is tough job. One of the problems is that we have
no idea just how idealized the lines are or if they were accurately taken
off.
Incidentally, Leo Lazauskas of the theoretical math department at the
University of Adelaide has been graciously running boats through his CFD
program GODZILLA. Eventually I hope he can run some traditional boats
through to see if he gets the same numbers I get with KAPER. For what they
are worth these are the resistance that KAPER predicts for the Dyson
baidarka (lines taken of drawings supplied by George).
The resistance are in pounds and start at 2 knots and increase in half knot
increments (displacement 215 lb.). At ten knots the average horsepower is
.524 which is not unreasonable and certainly within the abilities of strong
paddlers. My feeling has been that KAPER under predicts chine boats since
it assumes a smooth flow and most chine boats will have some flow across
the chine. I have yet to establish this to be true for all chine boats
though.
0.786 1.179 1.639 2.183 2.859 3.711 4.815 6.342 7.721 9.500
11.263 12.879 14.256 15.325 15.981 16.527 17.078
I seem to have lost the data from Savitsky's formula for planing boats but
will run the boat again to see what it was.
Cheers
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://www.onlink.net/~jwinters