[Paddlewise] Stability

OK I don't have enough to do!!!

I ran the stability check again at 1,2,3,and 4 degrees.

These are the righting arms I got. The box shape is like the one on Nick's 
web site. The "V" bottom has the chine just slightly above the waterline 
(.0011') . I chose these shapes in order to better reveal possible 
differences. Clearly similar shapes will have less variability. For example, 
a chine boat versus and similar round bilge boat with a similar section 
co-efficient.

For the "V" bottom the righting arms are:

1 degree 0.0163
2 degrees 0.0301
3.degrees 0.0417
4 degrees 0.0515

For the Box shape;

1 degree 0.0185
2 degrees 0.0379
3.degrees 0.0569
4 degrees 0.0759

Now, you can see the difference and even draw the slopes yourself. However, 
there is another way to look at it. Suppose I set the CG relative to the 
bottom of the boat instead of relative to the waterline. In that case you 
get a different set of numbers which are for the box shape:

1 degree 0.0163
2 degrees 0.0326
3.degrees 0.0489
4 degrees 0.0654

You can see that for that set of parameters Nick is dead on. However, the 
beams do not always force a higher CG and I used the same height for both 
relative to the waterline because that allowed suitable seat width.

As Nick points out at 1 degree and a CG relative to the bottom they don't 
differ at all but beyond that shape has an increasing effect. This is why I 
believe one should look at the shape of the curve and not points on the 
curve. If you have ever designed racing boats you will recognize the 
unreliability in measurement points in assessing performance.

Now, I can't comment on how well paddlers will notice the differences. I 
don't feel paddlers are as sensitive as some claim but I seem to be a 
minority on that. I suspect that those of you who an sense small differences 
in performance should have no trouble withs sensing  differences in righting 
arm over five percent.

I think it would be fun to run Nick's shapes etc. since I have always 
wondered about the variability in programs. I think Nick uses Macsurf. I use 
Nautilus.

Cheers

John Winters
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