[Paddlewise] Stability

Nick wrote originally;

>>  Primary stability has almost nothing to do with the cross sectional
>> shape of a boat. Chines, no chines, makes no difference. It is the
>> shape of the water plane and the height of the center of gravity that
>> will determine initial stability.

This sounded pretty strong to me so I ran some tests of my own and got 
different results. Nick sent me his data and it revealed that Nick had 
varied the CG in each test hull. This seemed like a no-no to me. When one 
wants to determine the effect of one variable the usual practice is to hold 
all other variables constant especially major variables like CG. Suppose, 
for example,  some one said that increasing waterline beam had no effect on 
initial stability. Most would laugh because experience tells us something 
much different. Suppose, however, that this person showed us data revealing 
no change in initial stability - results he got by changing the CG with each 
change in beam. I suspect we would quickly point out the error of his ways. 
Whether one thinks it matters a lot or not is another issue.

I suspect that the hard chine and round bilge proponents think it does.

There is another issue. On Nick's "V" bottom boat he put the chine below the 
waterline. At small angles of heel the in and out wedges of volume are the 
same as the box shaped boat which helps explain why he got little or no 
difference. In my test I set the chine just above the waterline giving a 
different righting arm by 5.2%. Most boats will fit some where in between 
these extremes.

More recently Nick wrote;

> And as a practical matter most kayaks have fairly similar water plane 
> shapes, what changes most
>significantly is the waterline width.

I wondered about that too so I picked out four boats (not completely at 
random) and found that they had waterplane coefficients that varied from 
0.674 to 0.609. Not sure what "fairly similar" means so maybe this much 
variation doesn't matter. "Fairly" similar sounds a bit "mushy" to me 
though. Of course beam  does have more impact but does that mean you ignore 
the waterplane?

Does any of this matter to paddlers? I don't know because I don't know how 
accurately paddlers can detect differences in stability. From a design 
standpoint a boat is composed of many small things as well as a few large 
things melded together to create a distinct boat. I recall Matt telling me 
once how he tweaked and tweaked his designs to reach what he considered the 
right boat. I bet some people would say he was just nit-picking but if you 
talk to the people who own his boats you will get a much different response. 
I suspect the same of Nick's boats and their owners.

The real question is "Does all this matter here at Paddlewise, in the 
Nit-picking capital of paddle sport?    :-)

Cheers

John Winters
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