Looking for input. I have been having some discussions about kayak "rollability". The common idea is a kayak will be hard to roll if it is stable upside-down. This makes sense initially, but then again most people can get most of the way up in a roll. The hard part is getting all the way. If inverted stability was the most important thing, getting from upside-down to the point where you can breath would be the hardest part. I thought that maybe the slope of the stability curve at 90 and 270 degrees would be a better indication of how easy a boat is to roll. A lower slope indicating and easier boat to roll, i.e. the effort required to change the angle fo the boat would be less. Any comments? 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_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Hi Nick, I have found my CLC Chesapeake 17 to be a bear to roll. It is fairly wide-beamed (24.5" at sheer, about 23.5" at waterline) and the hard chines seem to drag a lot of water when you're rolling up. It is VERY difficult to get near 90* (either from 0* to 90* or from 180* to 90*). I would say that its stability curve is great from 0* to 50* and from 140* to 180* but it doesn't want to stay near 90* for long. Of course, these numbers are all subjective, and I've never seen the actual curves for this boat, but I would quantify it as a not-so-easy-to-roll boat. Of course, Greenland kayaks have hard chines, so my hard-chined opinion is probably worthless. As for getting most of the way up--are you postulating that people get their bodies most of the way up (but not the boats) and fail as a result; or that people get the boat most of the way up, but fail on the way to getting their bodies and heads into an oxygen-rich environment? A very low aft deck and aft coaming also contribute to rollability, as it allows for a much lower center of gravity, and a smaller righting arm in the kayak/kayaker system. There are boats out there with narrower beams and rounder hull sections that feel a lot easier to roll--the CD Extreme, Prijon Topolino and Topo Duo, and your Guillemot come to mind. Yeah, I'll buy that a relatively flat stability curve from one angle to the next would make for a more easily-rolled boat. I would also think that a lower curve on a stability graph would make a more easily rolled boat than a curve of the same slope with higher points. -- Shawn W. Baker 0 46°53'N © 2000 ____©/______ 114°06'W ~^~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ baker_at_montana.com 0 http://www.geocities.com/shawnkayak/ *************************************************************************** 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/ ***************************************************************************
At 11:01 AM 06/29/2000 -0600, Shawn W. Baker wrote: >I have found my CLC Chesapeake 17 to be a bear to roll. It is fairly >wide-beamed (24.5" at sheer, about 23.5" at waterline) and the hard >chines seem to drag a lot of water when you're rolling up. It is VERY >difficult to get near 90* (either from 0* to 90* or from 180* to 90*). >I would say that its stability curve is great from 0* to 50* and from >140* to 180* but it doesn't want to stay near 90* for long. Shawn, Your subjective numbers match my own experience pretty well. My CLC 17 is equally difficult to roll. I'm curious if other CLC owners will defend their craft and its ease of rolling. My rolling instructor kept wanting to get me out of my own boat and into his surfing kayak -- but of course if/when I ever really need a roll it will be in my boat, not his. Part of the problem with the CLC is that there is too much butt room and plentiful knee room and I have not tightened it up with pads. (We won't get into the operator's deficiencies.) The CLC does not have a lot of peaked bow (like a Guillemot or a Necky Looksha IV). My unscientific and inexperienced eye tells me the peaked bow should make a boat unstable upside down (that's a good thing). The CLC does not have the high volume "West Greenland" bow like the Pygmy Queen Charlotte, which I suspect would make that boat help you up to 90 degrees. Gotta try one out. My CLC has a rudder. While the rudder was tied down during rolling sessions, it still adds a lot of resistance to the first portion of the roll and adds deck weight once it clears the water. I've tried a fair number of different sea kayaks and my own opinion is that the CLC (without rudder) has less directional stability & tracking than other 17' boats, so the d**ned rudder is a necessary evil. Well, I've finished the process of repairing my keel, where the fibreglass was worn through in several spots. I dyed the epoxy blood red all along the keel so you will see me from a thousand miles whenever I try to roll the boat again. The important thing is now I can get the boat on the water again and all will be forgiven. jerry. *************************************************************************** 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/ ***************************************************************************
Having been away from the list for a week and not having had time to read all of the 169 e-mails which arrived during that time, this may not contribute much to the discussion, but FWIW: The CLC Cape Charles 17 (17' X 23") I built for my wife a few years ago is the most difficult boats I've rolled. A CLC Patuxent 17.5 (17.5' X 21") I built a year later is moderately easier to roll, but still not easy. Both boats are hard-chined with lots of flare to the sides. The Cape Charles has a great deal of initial stability and excellent secondary stability. The Patuxent has relatively little of either sort of stability. A hard-chine Seguin (17' 10" X 22") I built has moderate initial and secondary stability, is much easier to roll, but still a lot more difficult than the boats in the next paragraph. I'd class all of these boats as having relatively deep keel-to-coaming dimensions. None of these is as easy to roll as a Romany (either length), a VCP Skerray, which are both round-chine, or a VCP Anas Acuta (hard chine)or Pintail (round chine). Romanys have very good stability, but are also very easy to roll. A hard-chine S&G boat I've just completed, 17' 6" X 22", with keel-to-coaming depth of 8.5", is almost as easy to roll as the Romanys are. My very non-scientific impressions: I think cross-sectional profile, shape(rounded vs hard-chine), width, and depth of the boat contribute a lot to ease or difficulty orf rolling. Logs are easy to roll. Wide flat planks, especially big ones, roll with difficulty. Low-volume boats roll a bit more easily. For those of us who enjoy doing layback rolls, shallow depth helps. Bill Hansen Ithaca NY *************************************************************************** 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/ ***************************************************************************
My subjective numbers were with an outfitted CLC 17. It's much easier to control with a good seat, hip pads, and knee pads, but it's still not a highly maneuverable boat (in any axis). I'm really surprised you can roll it at all, especially without the knee pads--when I first tried rolling mine sans pads, my knees kept sliding around. Shawn Jerry Hawkins wrote: >Part of the problem with the CLC is that there is too much butt room and plentiful >knee room and I have not tightened it up with pads. (We won't get into the >operator's deficiencies.) -- Shawn W. Baker 0 46°53'N © 2000 ____©/______ 114°06'W ~^~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ baker_at_montana.com 0 http://www.geocities.com/shawnkayak/ *************************************************************************** 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 wrote; > I have been having some discussions about kayak "rollability". The common > idea is a kayak will be hard to roll if it is stable upside-down. This > makes sense initially, but then again most people can get most of the way > up in a roll. The hard part is getting all the way. If inverted stability > was the most important thing, getting from upside-down to the point where > you can breath would be the hardest part. > > I thought that maybe the slope of the stability curve at 90 and 270 degrees > would be a better indication of how easy a boat is to roll. A lower slope > indicating and easier boat to roll, i.e. the effort required to change the > angle fo the boat would be less. > A few thoughts: Lower stability when upside should make rolling easier particularly when you factor in the righting moment of the life jacket/paddler. I would suspect that the deck shape along the sheer impacts as well since the boat rolls rather rapidly. A rounded sheer such as Nick uses on some of his boats should roll more easily than a more angular sheer (such as I use on some of my boats). The narrower the boat the easier it seems to roll in both directions - up and down. One could calculate the rolling resistance of the shape and merge that with the upside down stability. Seems like a lot of work when taking a boat out and rolling it tells whether you find it easy or difficult to roll. Of course, none of this applies to owners of wide kayaks who consider rolling something "other" people do and people like myself who has done it and can't imagine why anyone would want to do it more than once. :-) 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 wrote; > >> I have been having some discussions about kayak "rollability". The common >> idea is a kayak will be hard to roll if it is stable upside-down. This >> makes sense initially, but then again most people can get most of the way >> up in a roll. The hard part is getting all the way. If inverted stability >> was the most important thing, getting from upside-down to the point where >> you can breath would be the hardest part. >> >> I thought that maybe the slope of the stability curve at 90 and 270 >degrees >> would be a better indication of how easy a boat is to roll. A lower slope >> indicating and easier boat to roll, i.e. the effort required to change the >> angle fo the boat would be less. >> >John W wrote: > >A few thoughts: > >Lower stability when upside should make rolling easier particularly when you >factor in the righting moment of the life jacket/paddler. I would suspect >that the deck shape along the sheer impacts as well since the boat rolls >rather rapidly. A rounded sheer such as Nick uses on some of his boats >should roll more easily than a more angular sheer (such as I use on some of >my boats). The narrower the boat the easier it seems to roll in both >directions - up and down. > >One could calculate the rolling resistance of the shape and merge that with >the upside down stability. Seems like a lot of work when taking a boat out >and rolling it tells whether you find it easy or difficult to roll. Of >course, none of this applies to owners of wide kayaks who consider rolling >something "other" people do and people like myself who has done it and can't >imagine why anyone would want to do it more than once. :-) Well that seems to leave an awful lot up to unreliable human judgement. Next you'll be saying people should just paddle a boat to determine how efficient it is. :) I won't try to convince you of the entertainment value of being able to roll. I agree with you to a large degree, but there is some value to being able to get an idea about rolling performance from looking at the stability curve. For one it is less open to different interpretations than descriptive characterizations of sheer shape. I agree that the shape of the sheer is effecting the easy of rolling, but how do you describe a sheer shape such that it will consistently characterize what is pertinent to ease of rolling. My hypothesis is that the slope of the stability curve supplies the information required in one easy-to-interpret format. The rise of the bow may also effect rollability, but some bows have a lot of volume while others don't. Again, you have the trouble of interpreting the data accurately. Wide flat boats with high inverted stability will be hard to roll. The slope of the curve will reflect this because the slope will increase to account for the large change from inverted to upright. But two boats with roughly equivalent inverted stability could have quite different rolling characteristics (due to different sheershapes or other factors) and I suspect the slope of the curve would reflect the differences. 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_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Nick wrote; > Well that seems to leave an awful lot up to unreliable human judgement. > Next you'll be saying people should just paddle a boat to determine how > efficient it is. :) Well, here I go trying to be conciliatory and I get rapped on the knuckles. No pleasing you guys :-) >I won't try to convince you of the entertainment value > of being able to roll. It must entertain people. No need to convince me. I have watched them roll after roll after roll and always seeming to have fun. Hey, some people like S&M too. Who can judge what constitutes fun? Not me but maybe someone else can. I hope no one thinks that I don't have fun paddling just because I don't roll at every opportunity. (Maybe I should ask Prof Inverbon how he feels about it. > some value to being able to get an idea about rolling performance from > looking at the stability curve. For one it is less open to different > interpretations than descriptive characterizations of sheer shape. No question about it, I agree that quantitative beats subjective hands down. But, I did not suggest descriptive interpretations of sheer shape. If one wants to apply quantitative measures to stability why not go all the way and calculate the roll damping characteristics of the upside down boat? Why just partial science? > I agree that the shape of the sheer is effecting the easy of rolling, but > how do you describe a sheer shape such that it will consistently > characterize what is pertinent to ease of rolling. My hypothesis is that > the slope of the stability curve supplies the information required in one > easy-to-interpret format. Does it provide the dynamic information. Keep in mind that the stability curve provide "static" stability. Rolling has a large dynamic component. Consider this, suppose a boat had stabilizing fins. They would not show up as a significant aspect on the static stability curve but would show up as a significant roll damping device. I will dig into my bag of books and see if I can find information on roll damping. > The rise of the bow may also effect rollability, but some bows have a lot > of volume while others don't. Again, you have the trouble of interpreting > the data accurately. Maybe not if you look at rolling phenomenon as the combination of righting moment and roll dampening. The bow could provide reduced static stability but increased roll damping. Neat Ehhh? > Wide flat boats with high inverted stability will be hard to roll. The > slope of the curve will reflect this because the slope will increase to > account for the large change from inverted to upright. But two boats with > roughly equivalent inverted stability could have quite different rolling > characteristics (due to different sheer shapes or other factors) and I > suspect the slope of the curve would reflect the differences. No question the stability curve reflects the static condition but how does it reflect the roll damping aspect? Can you establish the degree to which each contributes? Suppose we looked at the upright condition and then related that to the upside down condition. What similarities exist? 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/ ***************************************************************************
The best discussion I have seen related to kayak rollability is located in the "Official Handbook of the British Canoe Union", in the chapter on Design and Selection of Equipment by Frank Goodman, pages 29 to 32. It includes several pages of excellent graphics and describes and illustrates the key relationship between the center of gravity and the center of buoyancy. It also illustrates the volume impact of higher or lower gunwales (or sheer) on roll stability. Bill McKenzie wamckenz_at_gte.net *************************************************************************** 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/ ***************************************************************************
Interesting discussion. I meant to post a note on this thread last week but got tied up with work. John Winter's posts have just reminded me what I was thinking. I'm not sure how much the inverted stability (or lack of it) is important to rollability. Someone pointed out that most non-rollers fail at the last hurdle - getting their body out of the water and over their boat. I don't think that the stability curve is necessarily an important factor in this, but rather the fact that weak rollers rely on momentum to help them up at the end .... and as Winters pointed out we need to consider roll damping. My observation rolling a variety of boats is that given roughly the same input they each have a speed which they roll at. white water boats / pool trainers come round really quickly and a roll like a c-c works effectively. I've seen people with what look like effective rolls in such boats surprised by sea kayaks though, which in general roll much more slowly (I presume after reading Winter's posts because of the roll damping effect of the boats shape). With the same input, by the time a rotobat would be up a sea kayak may be only one quarter the way around, and if the roller has run out of momentum, or been surprised at not being up and stalls the paddle, the roll fails. The rolling input therefore needs to be timed to the boat, and a quick explosive input can be less effective than prolonged support from a slow screw roll or sculling rolls. On a similar note my observation of rolling fully loaded boats is that the laden boat with its increased inertia is further slowed down when rolling. Ditto deck gear, spare paddles and deck bags etc. If you rely on just setting up then going through the motions to roll without being aware of what the boat is doing then different levels of roll damping will feel like they make a roll harder - but the boat may be just as 'easy' to roll, you just need to match your input to the boats speed of rotation. My point is I guess that like much about boat handling its hard to isolate familiarity with a boats characteristics to the performance effect of the boats shape. The new generation of extreme play boats like 'Mr Clean' introduce another dimension ... with such little volume in the ends of very short boats the fore/aft pitch stability, or lack of it, adds another level of complexity. Apply paddle support for a roll at anything other than 90 degrees to the boat and it either spins or stands on its tail .... Cheers Colin Calder 57º19'N 2º10'W *************************************************************************** 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/ ***************************************************************************
>> My very non-scientific impressions: I think cross-sectional profile, shape(rounded vs hard-chine), width, and depth of the boat contribute a lot to ease or difficulty orf rolling. Logs are easy to roll. Wide flat planks, especially big ones, roll with difficulty. Low-volume boats roll a bit more easily. For those of us who enjoy doing layback rolls, shallow depth helps. Bill Hansen Ithaca NY >> Like Bill, I've been away for a while, so I'm very late to this thread. There is no doubt to me that some kayaks are easier to roll than others. One thing I've noticed that seems to make difference that no one else has mentioned is flare. It seems to me that kayaks with a lot of flare in the midsection, such as Sea Lions, tend to flip quickly once the gunwale dips below the surface; these kayaks are harder to hold on edge, and take more effort to get the gunwale above water. An easy-rolling kayak like the Romany, in contrast, has nearly slab sides and is also easy to hold on its side by sculling. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced/forwarded 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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