[Paddlewise] Secondary stability... another way to think about it

First off, I don't like Nick's suggestion that the position of the 
inflection point is a good metric for comparing the relative stability 
between different kayaks. I think a kayak with the most secondary stability 
has a peak that occurs with the most amount of kayak tilt. In other words, 
the further to the "right" is the peak, the more stable is the kayak. But 
the force vs. tilt angle curves are somewhat misleading anyway because they 
ignore the essential physics of a boat-paddler combination. This has 
undoubtedly led to some of the challenge in discussing  the issue... (I'll 
keep my theories secret on the origin of the rest... hehee :)

Let's get back to the basic physics of staying upright. It's simple, right? 
If the center of gravity of the paddler is directly above the center of 
bouyancy of the boat, the boat-paddler system remains upright and dry. If 
the paddler tilts the kayak, which shifts his CG to the side, then the CB 
of the boat must also shift by the same amount, or else a capsize occurs.

What happens when a paddler-kayak system is tilted:

CG: For low angles of edge, the CG will essentially remain stationary 
because the paddler compensates by bending his spine ("J-lean")
For higher angles of edge, the CG will start to move laterally towards to 
edge of the kayak due to physiological limitations of the spine.

CB: For low angles of edge, I would expect that the CB would move towards 
the side that is being edged in all cases. As larger angles of edge are 
applied, the CB may continue to move sideways, but eventualy it will stop 
moving or even move back towards the center of the boat. It  is at the 
point where the CG stops moving outward that the boat will no longer be 
stable for increasing amounts of edge. Essentially, this is the limit of 
secondary stability.

Now here's my question... the location of the CB with varying degrees of 
tilt should be just as easy to calculate as the bouyant resistive force, if 
not even easier. Why doesn't someone modify a program to measure this? I 
think it would be a lot easier to quantitatively understand the secondary 
stability of kayaks by this metric.

I guess I'm never one to skip an opportunity to add fuel to the fire... Cheers,
Kevin

ps. I'm going paddling tomorrow in my brand spanking new Riot Prankster. 
That's a rodeo boat for big boys (like me)... it's much too cold to paddle 
anything but rivers these days.


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