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/ ***************************************************************************
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 > >*************************************************************************** >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/ >*************************************************************************** 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!"<<<< *************************************************************************** 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/ ***************************************************************************
>> Observe the freaks who can roll with their hands behind their head. I have never seen this. How is it done? Does the paddler hip-snap back and forth while upside down to set the boat in a sidewise rocking motion, and then come up on one last powerful snap? I would appreciate a detailed description of how this is done. I've also heard that some people can roll up with their hands crossed on their chest. I'd appreciate a description of this also. *************************************************************************** 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/ ***************************************************************************
On Tue, 4 Jul 2000, Jack Fu wrote: > >> Observe the freaks who can roll with their hands behind their head. > > I have never seen this. How is it done? Does the paddler hip-snap > back and forth while upside down to set the boat in a sidewise > rocking motion, and then come up on one last powerful snap? I No, the ones I've seen do it just like a regular C-to-C. > > I've also heard that some people can roll up with their hands > crossed on their chest. I'd appreciate a description of this also. Same thing. If you really want to be impressed, look up some of Nolan Whitesell's videos. He does the arms crossed roll, but in an open canoe. Steve Cramer *************************************************************************** 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/ ***************************************************************************
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/ ***************************************************************************
Looking at the roll period from 90 degrees to 270 degrees ( Zero being upright) with the paddler hanging stiff does not strike me very relevant to how easy the boat is to roll. The interesting part of rolling is going from 180 to 360 degrees. It is this portion of the rotation that is important, and the hardest part of the roll is typically from 270 to 360 degrees so determining the damping of the inverted boat (90 to 270) does not even address the section of the roll where most people (who know how to roll) fail. I was attempting to teach a friend to roll yesterday, he could always get his body to the surface of the water and the boat rotated to 90/270 degrees. He just couldn't rotate it beyond towards vertical. If the paddler is hanging stiff he would provide resistance. But as Bruce said, typically the paddler moves his body counter to the rotation of the boat, so instead of providing resistance to the roll, his body provides assistance, or at least very little resistance. The body drag is more of a factor during the setup, but this is not a factor of boat design. While inverted drag may contribute to how easily a boat rolls, it seems to me that the hardest part of the roll does not include the inverted section. Why evaluate the whole chain when you can just look at the weakest link. I think the most useful evaluation of rollability should concentrate on the part of the roll which is hard. If this is the case, the rotational drag that would seem to matter the most would be from 270 to 360 (or 90 to 0). This would be a good thing because trying to estimate the drag of the paddler is messy where modeling the drag of things such as rudders, skegs and hard chines should be a little more straight forward. > > >> 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/ >*************************************************************************** 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!"<<<< *************************************************************************** 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/ ***************************************************************************
Nick wrote: >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. John commented negatively on this. I'm arguing from my own experience, which is primarily (as far as rolling is concerned) in whitewater boats. I think my body movement in the roll is small, relative to the water: I tend, if I remember correctly, to lie out near the surface before the roll motion starts. I'm not as negative on rolling as John is, but I tend to try to avoid them, and I haven't done any since a few practices last year, so I'm afraid my memory is a bit vague. My memory is that my body motion is intended to minimize its motion through the water, so the drag of the body is minimized. > >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. I suspect it depends on how well the roller "listens" to the situation. If you try to do an instant whitewater roll in a heavily laden sea kayak, the difference in roll periods will hurt you. If you recognize that you need to do things more slowly, no big deal. >{snip} >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 disagree here, Nick. Things that stick out, like keels, rudders, chines,... can make it nearly impossible to roll a boat quickly while the static stability characteristics, whatever ones are relevant (which was your original question, and I don't know the answer either), can make it very easy to roll slowly. So the question is as usual more difficult than one might at first hope. Bruce Winterbon bwinterb_at_magma.ca http://magma.ca:80/~bwinterb The only sustainable growth rate is zero. *************************************************************************** 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/ ***************************************************************************
Nick wrote; > Looking at the roll period from 90 degrees to 270 degrees ( Zero being > upright) with the paddler hanging stiff does not strike me very relevant to > how easy the boat is to roll. I agree and hope no one got the idea thta I looked at it that way. >The interesting part of rolling is going from > 180 to 360 degrees. It is this portion of the rotation that is important, > and the hardest part of the roll is typically from 270 to 360 degrees so > determining the damping of the inverted boat (90 to 270) does not even > address the section of the roll where most people (who know how to roll) > fail. I can't comment on this since I do not know where most people fail. (SNIP) > > If the paddler is hanging stiff he would provide resistance. But as Bruce > said, typically the paddler moves his body counter to the rotation of the > boat, so instead of providing resistance to the roll, his body provides > assistance, or at least very little resistance. The body drag is more of a > factor during the setup, but this is not a factor of boat design. Good point that I had not considered so maybe we can delete the body effect on damping. On the other hand, maybe the fact that people don't use their body that way contributes to their failure rate so maybe it does have a negative impact on those who don't roll well. > While inverted drag may contribute to how easily a boat rolls, it seems to > me that the hardest part of the roll does not include the inverted section. Is the boat rotating at that point? If so it would seem that its shape influences rotational drag. > Why evaluate the whole chain when you can just look at the weakest link. I misunderstood your original question. I thought you asked about rolling as a dynamic phenomenon in its entirety and not rolling just when it got difficult. Since I misunderstood I will respectfully bow out of the discussion. 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/ ***************************************************************************
>Nick wrote; <snip> >> Why evaluate the whole chain when you can just look at the weakest link. > >I misunderstood your original question. I thought you asked about rolling as >a dynamic phenomenon in its entirety and not rolling just when it got >difficult. Since I misunderstood I will respectfully bow out of the >discussion. You probably didn't misunderstand my original question. I posed a hypothesis for rollability that looks at the greatest force required, you countered with one that looks at total energy required. I am not convinced one way or the other. That is why I threw the idea out for comment. A similar question could be asked about stability: which boat is more stable, the one with the highest maximum righting moment, steepest initial stability, or greatest area under the stability curve, or none of the above. I think you could probably make rational arguements for each. Nick 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!"<<<< *************************************************************************** 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/ ***************************************************************************
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