Re:Canoe and Kayak Stability Factor

[Marven]

Hi Brian,

What you’re describing here (the distance between the transverse center of buoyancy and the center of gravity located at the keel) is already available in the extensions and is called KN Sin(phi)where K is the VCG at the keel and N is the N is the intersection of the center line and a vertical line through the center of buoyancy. In order to obtain the righting lever you have to extract VCG*Sin(phi). This is an exact measure of stability, but after that they fiddled with the numbers. Why is not very clear to me, because dividing a measurement by a constant value makes no sense when comparing two canoes of the same type if the KN*Sin(phi) of the second canoe is divided by the same constant. The ratios remain exactly the same, only the numbers will be smaller.

Comparing the righting levers is a good indication but not enough I’d say. Since the KN*Sin(phi) is mainly determined by the shape of the canoe you’re only comparing the shapes. Two canoes of exactly the same shape but different weights (lets say an ultra light canoe and a very heavy one) give the same KN*sin(phi) and therefore the same “stability number”. Better would be to include the weight of the canoe, which results not in a righting lever but a righting moment if you multiple the righting lever by the displacement. The resulting number are still easy to compare but by including the weight in the equation two similar shaped canoes of different weights would yield different stability numbers.

Of course you could also multiply the stability number calculated according to the method of Steve Killing with the weight of the canoe.