Re: [Paddlewise] Hull speed

"Blaauw, Niels" <nblaauw_at_foxboro.com> wrote:

<SNIP>>>>>>>I am planning to put the efficiency of my boat to the test, in a
scientific
way. My idea is to gather a handful of different kayaks and test them one by
one, by putting a weight in the seat, towing them behind a motorboat at
different speeds, and measuring the force needed to tow the kayak at each
speed. I can use a GPS to control the speed. A device to measure force is
cheap enough to buy just for the occasion.
My questions are:
- - Did anybody ever perform such a test and if so, what were the results. I
am specifically interested in performance of the Seayak, but also in general
differences in hull design, boat length and hull material;<<<<<<SNIP>

In the mid to late seventies I started testing the top speed of kayaks over
a short course (next to a floating bridge out of the wind). Pushing as fast
as I could go for about a minute my times for the same kayak was very
consistent. This is a good way to test kayaks you want to use for racing,
but it won't tell you much about the kayak's efficiency at cruising speed
(the important parameter for a sea kayak).
The first method I thought might work for testing drag was to get a bunch of
different kayak owners to meet at a river bridge and then have one paddler
(to keep the weight of "cargo" the same) hold a low speed (tube type) speed
meter over the side of the kayak (to test that the current had remained
constant). He would remove the knotmeter from the water and others on the
bridge would read a surveyor's scale fixed to a point on the bridge with a
line or wire to the kayak while he sat in the kayak and held still. The
water speed in the same place on the river was expected to stay fairly
constant and we would have the knotmeter to check if it changed over time.
I kept a lookout for suitable bridges but we never did do this so I don't
know how well it would work in reality. Of course, even if worked well it
might be difficult to get results at different kayaking speeds.
Back in the mid 80's when John Dowd the editor of Sea Kayaker magazine
wanted to do kayak testing in a very scientific way we tried to come up with
ways to test the drag of kayaks in a simple inexpensive way. Because I had
already been thinking about simple and cheap ways to do this since my
brother and I first started sea kayaking I already had a few ideas how it
might be done and tried to help out.
Other ways we thought of back then were towing by a boat, but I wondered if
the boat speed could be held constant enough. One way to compare kayaks
directly would be to set up a balance beam to tow both kayaks at once and
see which one drags back. Then switch sides to confirm the results. A set of
"standard" kayaks (or a shape that could be altered in a consistent way)
could be developed and tested against the new kayak to find its place in the
hierarchy. The advantage would be that the knotmeter would not have to be
really accurate or even consistent. The disadvantage would be the number of
test runs required (lots of powerboat time).
At that time I started to work on a way to run a knotmeter, clock, and a
scale (or strain gauge) through an analog/digital converter and into a small
computer (these functions are all integrated today and the devices can be
quite inexpensive --just a few hundred dollars). Before I really got going
on this Sea Kayaker got a special research rate on ship model testing time
at the University of B.C. test tank and I dropped my efforts.
Now what I would like to do is install strain gauges on a paddle shaft and
run that data along with knotmeter data into analog/digital
converter/computer device. I think something like this would be the best way
to test and compare kayaks (using the same paddler--or rotational sensors as
well) because, as opposed to a tow, yawing effects (due to the offside
paddle strokes) that probably differ with kayaks would also be accounted
for. If somebody wants to do this, contact me and I can save you some effort
by telling you what I have already found out about how this might be done.
The Prijon Seayak is one of the kayaks Sea Kayaker reviewed and I have run
through the mathematical programs that we (John Winters and I) devised to
estimate drag. Here are the results from John's estimating method for the
kayaks reviewed that you may have access to. The numbers range from drag in
pounds at 1.5 knots to 6 knots in 1/2 knot increments. I hope they stay nice
and neat in columns (like they were when I send them off into cyberspace).
You can download this spreadsheet off our website in the "downloads"
section. Keep us informed if you do any testing.

Speed in Knots    	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6

Seayak
Rtp (total for plastic)	0.58	0.99	1.51	2.09	3.01	4.36	6.01	8.83	11.96	14.09

Orca by Pyranha
Rt (total resistance)	0.54	0.92	1.37	1.92	2.76	3.96	6.04	8.65	11.62	14.53

Yukon Eski (Composite)
Rt (total resistance)	0.53	0.91	1.36	1.88	2.61	3.69	5.14	7.65	10.33	12.31

Artisan Millennium (Kayak Sport)
Rt (total resistance)	0.54	0.92	1.38	1.92	2.59	3.54	5.11	7.76	10.60	13.81

Avalon Viviane
Rt (total resistance)	0.56	0.96	1.44	2.01	2.68	3.53	4.80	7.19	10.26	13.38

Prijon Kodiak
Rtp (total for plastic)	0.57	0.97	1.50	2.08	2.82	3.85	5.44	8.11	10.96	14.03

Matt Broze
http://www.marinerkayaks.com


***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************