Re: [Paddlewise] Rudders/ frequency

Bob wrote;

>For relevance, what percentage of a "good paddler's" energy goes into
>maintaining direction?  It would seem to be over 10% for most paddlers
>under most conditions.

Wish I knew. This is a huge variable. There are no studies that I know of
but it would be relatively easy to calcuate the loss in energy between a
sweep and straight ahead stroke.  What is more difficult are the
biomechanical losses. The tank data showed what the drag was under ideal
conditions i.e. no stall no surge, no heave, no sway, no yaw. It also only
showed what happene with the rudder tested. There is a huge amount of data
on the drag characteristics of airfouls that is directly applicable to
boats. In fact it is regularly used to design boats, particularly keels and
rudders for sail boats. The difference between foils is easily calculated
as is the stall angle. Our good friends in the aircraft business have done
all the hard work. No question that an properly shaped airfoil ruder would
be an improvement over the common flat plate.

Dan wrote;

>This is an excellent question. In my experience, however, it seems as
>though it is more like 3 to 5 percent--certainly far less than 10
>percent. But this is based on a subjective judgement, and it is very
>much dependent on the boat being paddled. I will be able to do somewhat
>more objective measurements once I get my Differential GPS system
>operational. (Is that John I hear groaning?) DGPS allows very precise
>measurements of speed. I can try to maintain constant effort with and
>without a rudder deployed in windy conditions, and measure the
>difference in speed. I would hypothesize that I will make better speed
>without the rudder. Of course the results could always be challenged on
>the grounds that I receive a psychological boost by paddling without the
>rudder. It is exceedingly difficult to run a test of this type with
>"airtight" controls.

This should be an interesting test. My experience is that I cannot maintain
a uniform power output. Certainly not uniform enough to say that I can
personally sense or measure small differences in resistance. Anyone who can
has a great future career as a test device. Test tanks using the most
sensitive measurement devices available (the Navy spares nothing in its
quest for speed) don't claim better than +/- 5% so a person who can do
better is going to be able to name his own price.

Nevertheless, such a test would be useful. For instance, if you ran a base
series of tests in calm, wind free conditions to establish a norm and then
ran tests in windy conditions at different angles to the wind you will be
able to get a good idea of leeway and drag effects. It would not be
necessary to have precise speed effects but only velocity made good in the
desired direction. This is something I don't think has been examined. Not
sure how you would control heading with accuracy.

I think the problem with trying to isolate rudder drag in these conditions
is that one may have trouble quantifying the true effect. For instance,
when paddling I rarely try to hold tightly to course. My boat wanders from
side to side with waves and the wind. I focus on the distant objective and
am only concerned with the end product. In other words, my feedback loop
has a lot of slop an delay. The tendency with a rudder may be to decrease
the delay and might actually make the rudder look worse than it is. If one
is constantly wiggling the rudder to keep precisely on course the drag will
naturally increase. I suspect that beginners are the worst for this and
think it is sign of seamanship to steer a perfectly straight line.

Marathon racing canoes use the sit-and-switch paddling technique which,
although the boat wanders about the mean course the end result is more
efficient than trying to adhere rigidly to the course with steering
strokes.

 Another interesting test would be to have skilled and unskilled paddlers
do the same series. It may reveal the relative importance of skill
development in efficient paddling. Maybe tests with  beginners and then
repeated tests as they improved.

Jerry wrote;

>Nevertheless, if I am just travelling, not playing, in these conditions,
it
>is much more relaxing and less tiring to deploy the rudder.  Any added
drag
>is more than compensated by the non-necessity for any course corrections
>which would be necessitated more by the chop than the wind.  In flat
>protected water, the added drag is noticeable and I generally raise the
>rudder, even in strong wind.

This is something that Dan's tests might shed some light on. It may appear
that one is working less but one doesn't really know what the net result.
Subjective evaluations are a mixed bag. Sometimes they are pretty good and
sometimes they are terrible. The problem is that you never know which until
some one does a quantitative evaluation.

>
>How well do you think the tank tests represent boat behaviour in wind and
>chop, with uneven paddle strokes?

Tank data is one part of the equation. The resistance will not get better
because of rough water, etc.. and will probably get worse. The net effort
(effective horsepower consumed) may get better or it may get worse. One
just doesn't know for certain.

For example. A while back Sea Kayaker published an article about a couple
who got into trouble. The male half said that at one point the boat
wouldn't turn even though the rudder was hard over. Why not? The answer is
rather simple.  They were making very little speed and the rudder was
stalled. the result was the rudder lost its turning effectiveness and,
because it was now stalled it was slowing the boat even more and they were
making more leeway and thus getting more weathercocking. The closed loop
just kept getting worse. Sailors known that, when the rudder stalls you
straighten it out to reattach the flow. Novice paddlers don't know this and
just keep making the problem worse.

Some of us may have experienced situations in heavy cross winds when the
boat was weathercocking and the harder we paddle on the windward side the
more the boat wanted to turn into the wind. It seems like a paradox until
one understands that it is leeway combined with velocity that causes the
turning moment and that  the corrective turning  moment is only working for
us while the paddle is in the water. During recovery the combined velocity
and leeway cause the boat to turn back to weather. Very frustrating and it
is times like that when a rudder, retractable skeg or a different boat is
much desired.

Michael wrote;

>The goal of racing is to win the race.
>Kayak camping/cruising is almost by definition, steping out of the 'race'
>alltogether

This is quite true but human nature being what it is one is always trying
to go faster or improve efficiency. There is, however, a practical reason
for more efficient boats and that is safety. If you are trying to avoid
being blown onto a rocky lee shore you will want a boat that can do it. A
water pig may be just fine when conditions are benign but could be
dangerous when the going gets tough.

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






***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.gasp-seakayak.net/paddlewise/
***************************************************************************