Nick wrote; > I question whether the paddlers body adds much damping which is significant > to how easily the boat rolls. (SNIP) If the water flows across the body the body has an effect on damping. How much effect? If you use a drag factor of 1.0 (probably reasonable for the body but I would gladly accept something else if you have data) then you need only calculate the rotational speed to determine how much resistance the body offers. Assume an area of 2 square feet and given 1 second to rotate 90 degrees it looks like 1.57' p/sec. Using Joessel's formula that gives roughly 4.33 pounds of resistance, about the same resistance of most boats traveling ahead at four knots. Now I would not state this as gospel but it seems more than insignificant even allowing for some error. > 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 suppose the importance depends upon the center of rotation. In any case we have to look at the sum of all damping effects not just one. maybe the rudder, body, bow, section shape all add up to a significant whole. > 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. I may have misread you on that. I got the impression you asked about the effect of boat shape on rolling not the just the effect on rolling when rolling got difficult alone. > 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. Why? > 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. I am not sure I understand your point. 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_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Tue Jul 04 2000 - 12:40:58 PDT
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