Re: [Paddlewise] chine and stability

So far so good

Matt wrote:

>Here you are confusing width below the waterline with chine. Chine is the
>turn of the bilge and a harder chine has the transition from bottom to side
>around a smaller radius. soft is more rounded. Both underwater shapes below
>are the same width.
\                        /      |                          |
  \                    /        |                          |
    \________/          |_____________|
>Both are hard chined when compared to a hull more like the second one but
>with rounded corners. The rounded cornered hull with vertical sides will be
>between the first and second hulls in initial stability. This contradicts
>Jed's assertion that hard chines are more initially stable.

Dead on. The same stability and stability curve can result from a chined or
round bilge boat. One should not generalize from limited experience. Chines
do reduce rolling periods if everything else reminas equal.


>Secondary
>stability consists of many things and I also don't have any exact
definition
>of it, and don't believe any exact meaning of the term has been agreed upon
> as yet.

Perhaps Jed had in mind the classic naval architecure definition of initial
stability which refers to the stability range in which the metacentric
height can reliably predict stability and is represented by the slope of the
righting curve. "Secondary stability" for sea kayakers and canoeists seems
to correspond to what naval architects sometimes call "Overall stability".
I had never heard the term secondary stability until I started paddling in
Canada.



>>>>>Softer chined hulls tend to lack this strong initial stability but
instead offer a smoother transition as you move from an even keel to tilting
the boat.<<<<<

>How would one show or detect a smoother transition? What should I look for
>on a static stability graph? All the graphs I've looked at seem to be
>relatively smooth.

True enough. Some hard chined boats have very high section coefficients (i.e
more boxy). They have a lot of initial stability and then the stability
drops like a rock at a certain point of heel. I would sayt this kind of boat
has  a small "range of stability".

>>>>Past 10°'s or so of lean takes us into the realm of secondary
stability.<<<<

>Has this been agreed upon somewhere and I've missed it all these years?
>Please let me know your source or sources for this.

See above on this. Some good sources for this "angle" would come from most
naval architecture books (some listed in my web site).

>>>>Try every boat that strikes your fancy. Let your senses and the artiste
in you make the decision. Paddling is an experience for the soul, not an
exercise in logical thinking. For ever point I've made someone will take
issue with the science, but no-one will tell you that one and only one
design
is best for all people! <<<<


Ahh, but one sp*ns*n fits all. :-)

In any case, how a boat feels or performs does not depend upon one
characteristic.

Cheers,

John Winters
Web site address http://home.ican.net/~735769




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