Re: [Paddlewise] Rollability

I question whether the paddlers body adds much damping which is significant
to how easily the boat rolls. Even people with terrible technique can
usually get their body to the surface of the water without much effort. In
a roll like the c2c the body is used to push against the water so the drag
of the body in the water is actually a good thing. Observe the freaks who
can roll with their hands behind their head.

I agree that damping will play a part, however again since the hardest part
of the roll seems to be the last 100 degrees or so, I don't think that
upspwept ends will play a large part. A rudder would tend to be more of a
hinderance than an upswept bow.

I don't see that the rolling period of the inverted boat would be that
pertinant as it would mainly provide information for a orientation which
most people don't have any problem getting beyond.

Timing how long it takes the boat to go from it's capsize point to fully
inverted may provide more complete information. But even this would put too
much emphasis on the inverted characteristics.

It seems to me that a boat that is easy to roll will be easy to roll showly
or quickly. Damping would be related to how fast the boat rotates. This
would suggest that the dynamic part of the equation would be less important
to whether a boat is easy to roll.

Nick



At 6:30 AM -0400 7/1/00, John Winters wrote:
>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
>
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Nick Schade
Guillemot Kayaks
824 Thompson St, Suite I
Glastonbury, CT 06033
(860) 659-8847

Schade_at_guillemot-kayaks.com
http://www.guillemot-kayaks.com/

>>>>"It's not just Art, It's a Craft!"<<<<


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