I have a Gloucester Light Dory gives brings anyone stepping into it an immediate and graphic definition of "initial" and "secondary" stability. At low angles of heel, this boat is "tender", very tippy, and anyone standing in this boat and incautious enough to lean or step to one side gets a heck of a shock as the boat suddenly heels. Then, the secondary stability kicks in, and the boat stops heeling, suddenly. In order to put the gunwhale under, I have to sit on the edge of the boat. It can't really capsize, as as soon as the gunwhale goes under, it wants to come back up again. Even completely swamped, it will return to an upright position, like a Popeye punching bag. A breaking wave could rotate it completely, but this is the only way I could see actually turning the boat over. Of course, fully swamped, it is impossible to bail dry, but that is another problem. The real problem is that as it comes up against the secondary stability, it stops, and anyone standing is quite likely to get pitched over the side (banging their shins painfully on the way). Then, the immense secondary or ultimate stability (and high freeboard) would make it difficult or impossible to get back aboard. (Fortunately, I have discovered this boat's stability characteristics by deliberate test in neck-deep water, not "under fire" in breakers. In most conditions, just stay seated, and the boat will take great care of you. Stand up, and it will try to chuck you out.) This boat has a narrow, flat bottom, hard chines, and immense flare. I offer it as an example of a boat with some of the characteristics that Matt and John have been trying to describe with curves. Is there any way you gentlemen could post pictures of the stability curves you are describing? It might be instructive to "design" hypothetical vessels, same length, same displacement, no rocker, no taper, just a midship section 15 feet long or so, to let everyone get a feel for the factors which affect stability. I realize, rocker, taper etc. do affect stability, but it would be good to try and isolate some of the factors, then see what they do to the stability curves. Rob. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Another boat with similar response is the Adirondack Guideboat, which has a relatively narrow waterline and a lot of flare. I created an example kayak to show this kind of stability curve which you can see at: http://www.guillemot-kayaks.com/Example.gif This boat is designed specifically to illustrate some of the concepts. I suspect that if anyone ever built this example it would fall well into the category John calls "notchy" and probably be quite annoying to paddle. But this shape permits a narrow, easily driven shape, while maintaining overall stability. Features which are valuable in working boats such as the Gloucester light dory or the Adirondack guideboat. Some sit-on-tops use this concept to permit a stable boat with a high center of gravity yet still be easily paddled. 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 - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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