Re: [Paddlewise] Rudders/ frequency

John Winters wrote:

> ... 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. ...

I'm not sure what that "+/- 5%" refers to, but if it is the error
associated with a single test, and if the error is random, then I would
think that averaging the results from repeated tests would improve the
accuracy substantially. In any event, it is relatively easy to test for
repeatability. There were some results of on-the-water tests posted to
rec.boats.paddle a while back in which a paddler tested various kayaks
in flat water along a measured course of one nautical mile. He tested
the boats at "maximum effort" and at "90% effort" (which he describes in
some detail). He claims that for his base boat (a Mariner II) at maximum
effort, his times from different runs are separated by about .02 knots
(!), which is less than one percent.  At 90% effort he claims that
repeated runs are within .05 knots (which is about one percent). These
results are NOT based on averaging, but are the absolute differences
between individual runs. (Maybe he should apply to the Navy for a
grant.) I am quite confident that I would do less well in terms of
repeatability between individual runs (especially in windy conditions),
but I would expect that averaging the resulting rudder/nonrudder ratio
from numerous repetitions would significantly improve the reliability of
the results.

John continues:
      
> 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. ...

This is a very important point. Trying to hold a boat on a rigid course
is inefficient. This introduces another variable into the test. A
paddler who uses the rudder efficiently may get better results than
someone who is trying to hold an overly rigid course, and so the results
obtained for one paddler might not be generalizable to others. The same
is true, of course, for the tests obtained without the rudder. Some use
a more efficient technique than others when paddling without a rudder.
The use of a rudder might increase total effort for some, while reducing
it for others. So even if this can be answered for a given paddler
(which is far from certain), others may question with justification
whether the results apply to them. The bottom line is that such tests
are probably not worth the effort.   

Dan Hagen
Bellingham, Washington
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