[Paddlewise] Rollability

I checked and came up with the following;

For zero speed one possible formula. B N = 19.25 *[ Abk * bbk^.5 +
0.0024LBd^.5]*(d^2*dN/(Cb*L*B^3*T)) (Hope I got the parentheses right. Took
some liberties with the symbols)

where B = damping ratio, N  = roll amplitude in radians, Abk = area of bilge
keesls (in this case probably the paddler), L = Length, B = Beam, d =
distance from centerline at load waterline to turn of bilge (sheer in this
case), T = draft, bbk = width of bilge keels.

Probably just good for approximation since the formula derives from
regression analysis of ships. Not quite the same for a kayak.

One practical possibility.

Capsize the boat with  a load equal to that carried and with the CG located
appropriately. Periodically roll the boat by depressing one side and time
the roll period. The longer the roll period the easier the boat will roll.
This measures the boat only and does not factor in the paddler. This test
measures the effect of both righting arm and shape.

To establish the impact of shape one could start with a boat with  no
upswept ends and a rounded sheer. Do the test  and then tape on ends, do the
test, and then tape on a sheer cum bilge keel and do the test. In this way
you can determine how much effect these components have.

Happy testing.


Cheers,

John Winters
Redwing Designs
Web site address http://home.ican.net/~735769

***************************************************************************
PaddleWise Paddling Mailing List - All postings copyright the author and not
to be reproduced outside PaddleWise without author's permission
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.paddlewise.net/
***************************************************************************