Re: [Paddlewise] A Secondary Definition!

Nick Schade wrote:

[snip]
> Secondary is a little harder to pin down. I think what people call
> "secondary" is the feel that it is taking progressively more effort
> to effect a change in the lean. Some boats, you lean a little bit,
> the boat responds, you lean a little be more, it responds about the
> same, more lean, similar response. Some boats, you lean, it responds
> a bit, lean a little more and it responds more than before, more lean
> and an accelerated response. Other boats, you start leaning and the
> boat responds, you lean more, and the boat doesn't respond quite as
> much, more lean, even less response. These last boats tend to be
> characterized as having good secondary stability. The boat "stiffens"
> as it is leaned.
> 
> This tendency can be seen in the stability curve by analyzing the
> slope of the curve. The rate of change of the stability indicates
> whether it is going to take progressively more effort to create a
> given change or progressively less. Mathematical types will look at
> the derivative of the stability curve.
> 
> Some curves start out steep and bend continuously downward. Others
> start out relatively flat, then curve upwards before straightening
> out and starting to bend down. These are the boats which "stiffen".
> The inflection point, where the curve changes from upwards tending to
> downwards tending will probably tell us something about "secondary"
> stability. (for those mathematicians still following, the inflection
> point is the maximum of the derivative, or the zero crossing of the
> second derivative)
> 
> The possible characteristics to look at for this form of "secondary"
> stability are: the slope of the curve at the inflection, the height
> of the curve at the inflection, the angle of lean at the inflection
> or the area of under the curve until the inflection point.
> 
> After a little thought, I am going to say a boat with "good"
> secondary stability will be one where the angle of the inflection
> point is the highest. This will be the boat where you can lean the
> boat the most before the ability to recover starts to fall apart.
> Beyond the inflection point, less and less effort will be required to
> create the same effect on the boat until you reach the top of the
> stability curve where the slightest increase in effort will cause a
> capsize.
> 
> I am certain, that a lot of people won't agree with this definition,
> but I think it does address some of the concerns.

Comment from the peanut gallery:  keep it up, you three (four?).  I'm learning
stuff here.

My (very small) two cents:  Nick's definition is an easy to measure and
quantify one, and seems to have a basis in physics.  However, perhaps a shot of
empiricism might be in order:

1. gather up half a dozen competent paddlers and half a dozen (varied) boats. 
(The paddlers have to be folks who regularly test the secondary stability of
their boats, not placid paddlers like me.)

2. put them into each of the boats and ask them to "test" each one for its
secondary stability.

3. have them tell an observer at which angle they begin to "feel" the secondary
stability, and have them rank each boat for its "secondary stability."

Then compare their results with Nick's criteria to see if experience (with all
the limitations Winters has delineated) jives with Nick's stab at a definition.

I think we need data to test Nick's suggestion, though the debate has been
interesting.  We might also find that the data show us nature has whacked us
upside our heads with the "real" answer while we were trying to test the one we
thought was correct.

-- 
Dave Kruger
Astoria, OR

***************************************************************************
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/
***************************************************************************