RE: [Paddlewise] chine and stability

Dear Matt, John and all,

It might be that Navel Architecture does not consider and define "secondary 
stability", as John points out, because it is not relevant to the vast 
majority of vessels.  Only in kayaks and perhaps smaller canoes can one 
even perceive such a phenomena since you more or less wear the kayak and 
control it by twists and shifts of your body.  In an ocean liner or 
freighter no one can feel secondary stability, it is a meaningless concept 
to the designer and the crew.  The same is true of sail boats, catamarans, 
fishing boats, etc.

Why would an industry attempt to define an undetectable, meaningless 
phenomena with no commercial application?  It is only kayakers that 
perceive it, and they are unique.  And since it appears to be largely a 
perceived phenomenon not apparently detectable on the stability curves, 
hence the difficulty in measuring it.

It had not even occurred to me until Matt mentioned that it does not show 
up on the stability curves.  One would think that in a kayak with good 
secondary stability, the curves would get steeper toward the top, and ones 
with low secondary stability would have more rounded, flatter stability 
curves.  But this is not the case so it must largely be based on perception 
of the kayaker.  Following the thread I was thinking back of all of the 
other types of water craft and vessels I have been in (or piloted), from my 
limited experience, this notion and terminology does not even exist.  Even 
on something as sensitive to body movement and weight shifting as a surf 
board, there is no concept of secondary stability. Curious.  Must be 
because it is irrelevant to most water craft.

It looks like if there is some measurable difference in secondary stability 
in hull designs it is up to the kayaking community (designers, 
manufactures, etc.) to figure out how to define and measure it.  Apparently 
no one else is interested or even cares.  You may even have to measure the 
kayaker's skill and coordination, and factor that into the physical 
parameters of the hull.

Peter


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