Okay, I can't express this in formal technical terms, but I think Ralph may be right (upright?) in feeling that a sponsoned folding boat could be more stable and self-righting than a hardshell of equal chine and beam. (I mostly use hard shells so I'm not biased in favour of folding boats.) The displacement of a hardshell is essentially static, changing only as the entire boat moves. The sponsons of a folder, in contrast, are squeezed at the bottom as they are pushed deeper into the water, and therefore expand into greater width and stability in the higher parts. When scuba diving in a drysuit, I experienced this dynamic stability in an undesirable way; the air tends to be squeezed up to your ankles and away from your body if you swim head down, and you become very stable upside down! (Practise let me deal with this without having to fight the suit, but some divers never get the knack, and so wear ankle weights to prevent inversion.) Comments on and corrections of this theory invited, especially from the boat designers and boffins on the list. N49°16' W123°08' ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
At 11:44 AM 09-04-99 -0700, Philip Torrens wrote: > >Okay, I can't express this in formal technical terms, but I think Ralph may be right (upright?) in feeling that a sponsoned folding boat could be more stable and self-righting than a hardshell of equal chine and beam. (I mostly use hard shells so I'm not biased in favour of folding boats.) >The displacement of a hardshell is essentially static, changing only as the entire boat moves. The sponsons of a folder, in contrast, are squeezed at the bottom as they are pushed deeper into the water, and therefore expand into greater width and stability in the higher parts. ...snipped... I long ago read an article on this very subject, complete with formulas, but it basically said what you so eloquently and succinctly described. Though the reference is long since lost, perhaps the design experts on the list, such as John or Nick, know of it. Regards, Leander overfall_at_ix.netcom.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Leander wrote: > > At 11:44 AM 09-04-99 -0700, Philip Torrens wrote: > > > >Okay, I can't express this in formal technical terms, but I think Ralph > may be > right (upright?) in feeling that a sponsoned folding boat could be more stable > and self-righting than a hardshell of equal chine and beam. (I mostly use hard > shells so I'm not biased in favour of folding boats.) > >The displacement of a hardshell is essentially static, changing only as the > entire boat moves. The sponsons of a folder, in contrast, are squeezed at the > bottom as they are pushed deeper into the water, and therefore expand into > greater width and stability in the higher parts. ...snipped... > > I long ago read an article on this very subject, complete with formulas, > but it > basically said what you so eloquently and succinctly described. Though the > reference is long since lost, perhaps the design experts on the list, such as > John or Nick, know of it. Philip's and Leander's comments remind me of something interesting about the way a sponsoned folding kayak behaves when it has taken on a lot of water. If you turn that folding kayak on its side, it will rise on the sponson on that side and spill a lot of the water out, up to about the inside level of the sponson. (It is a neat way to begin partial emptying of a folding kayak that most people don't know about. The phenomenon is even more pronounced if you also have flotation bags fore and aft as you alway should in any folding kayak or non-bulheaded kayak.) If there were no different in the displacement effect between a hardshell and a folding kayak with sponsons, then this float-up phenomenon would also happen with a hardshell laid on its side. To my knowledge, the hardshell would not at all rise that way to spill out the water, only the sponsoned kayak would. That column of compressed air in the sponson is fighting its way to the surface. In a corollary way, it also resists being submerged. Philip's idea of a dynamic as opposed to static displacement certainly has a ring to it that shows itself in real life. There are so many ways of skinning a cat in the kayaking world. Some corners of this realm offer some unique advantages that some people don't seem to want to hear about or want to put outside the kingdom's gate as not worthy. For example, the earlier sit-on-top kayak discussion that I engendered that drew some flak. But let's face it, there ain't nothing easier to empty than an SOT nor much easier to get back into without pumps, paddle floats, re-enter and roll and all that. Also the middle range of SOTs are every bit as fast as the middle range of beamier hardshells made of polyethylene and are considerably stable. Performance kayaks require performance paddlers and a lot of people getting into kayaking are simply not going to work at getting and keeping the skills. Wouldn't these paddlers be better off with kayaks that are less skill reliant? ralph diaz -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
rdiaz_at_ix.netcom.com wrote: > Performance kayaks require performance paddlers and a lot of people > getting into kayaking are simply not going to work at getting and > keeping the skills. Wouldn't these paddlers be better off with kayaks > that are less skill reliant? > There's been many well and reasoned arguments, but I don't like this point. The sea is not our native environment. It's dangerous out there! Sure self-rescue is easier on a SOT. But I'd wager that overconfidence has killed many more people than those who may have been saved by SOTs. I'm concerned about the message being put out that having a SOT is a substitute for having skills. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Berkeley Choate wrote: > > rdiaz_at_ix.netcom.com wrote: > > > Performance kayaks require performance paddlers and a lot of people > > getting into kayaking are simply not going to work at getting and > > keeping the skills. Wouldn't these paddlers be better off with kayaks > > that are less skill reliant? > > > > There's been many well and reasoned arguments, but I don't like this point. The sea > is not our native environment. It's dangerous out there! Sure self-rescue is easier > on a SOT. But I'd wager that overconfidence has killed many more people than those > who may have been saved by SOTs. I'm concerned about the message being put out that > having a SOT is a substitute for having skills. I don't believe that I said anything about _substituting_ for having skills; I said _less_ skill reliant. And the skills that would play less, if no role at all, are in a part of my statement you snipped out which I quote back in here below. Without these antecedent sentences in the very same paragraph, you are making me out as advocating going out willy-nilly into the briny, which I am not. Give me a break, Berk.: >> "Some corners of this realm offer some unique advantages that some people don't seem to want to hear about or want to put outside the kingdom's gate as not worthy. For example, the earlier sit-on-top kayak discussion that I engendered that drew some flak. But let's face it, there ain't nothing easier to empty than an SOT nor much easier to get back into without pumps, paddle floats, re-enter and roll and all that. Also the middle range of SOTs are every bit as fast as the middle range of beamier hardshells made of polyethylene and are considerably stable. Performance kayaks require performance paddlers and a lot of people getting into kayaking are simply not going to work at getting and keeping the skills. Wouldn't these paddlers be better off with kayaks that are less skill reliant?" << A paddler in an SOT functions perfectly well without a pump or paddle float. He/she does not need to know a self-rescue cum float nor how to roll or to do a reentry and roll. Nor even learn a wet exit since there is nothing to be entrapped in via a sprayskirt. Moderate bracing skills suffice for most SOTs since they are quite stable. The SOT substitutes for THOSE SPECIFIC SKILLS (paddle float reentry, working a pump while sculling, etc.) that have been meat and potatoes discussions on this listserver for these long months of the northern hemisphere winter. They are unnecessary in an SOT. My specific point is that the seakayaking community should not look down its collective nose at a kayak that obviates skills that take time and which many people won't do. So you wind up with a lot of paddlers who are out there in kayaks that they have not wet exited out of and could be entrapped if wearing the de rigueur neoprene tight fitting skirt. Or they are carrying a paddle float which they have never used but did see pictures about in some book and feel they can do a self rescue with the float when the time comes. Lots of the paddlers I see out there are exactly in that predicament and would be better off in kayaks that don't require that they can do such things. An SOT may not have the panache of a sleek, small cockpited kayak with upturned bow for landing on ice floes but the SOT is more practical, easier to work with, more forgiving vessel for doing the kind of paddling most people do in the waters most people venture on to. Of course a paddler in an SOT needs skills, just not _those_ I premised my statement on. First of all, the SOT paddler should know weather, wind and currents patterns in the area as well as waterborne traffic situations on the route of travel. He or she should be dressed for the water temperature and for definitely getting constantly wet, even more so than a SINK (Sit INside Kayak), since he/she is more exposed and not slightly cocooned inside under a sprayskirt. He/she should learn good paddling technique to be efficient in paddle strokes and control the SOT in beam and quartering wind and weather conditions and following seas. Should have emergency gear with them at all times (extra clothes, energy bars, space blanket) plus signaling devices (flares, mirror, and know how to use them) and night illumination (flashlight, strobe, etc) and, of course, wear a PFD. Etc. Now, I know many paddlers do want to develop the other skills and have kayaks they can perform these skills in. But there are other forms of kayaks, such as the SOT or folding kayak, which can venture on to the same waters without some specific skills that are really a must in certain esteemed kayak forms. ralph diaz -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
rdiaz_at_ix.netcom.com wrote: > > Leander wrote: [?] > > > > At 11:44 AM 09-04-99 -0700, Philip Torrens wrote: > > > > > >Okay, I can't express this in formal technical terms, but I think Ralph may be > > right (upright?) in feeling that a sponsoned folding boat could be more stable > > and self-righting than a hardshell of equal chine and beam. (I mostly use hard > > shells so I'm not biased in favour of folding boats.) > > >The displacement of a hardshell is essentially static, changing only as the > > entire boat moves. The sponsons of a folder, in contrast, are squeezed at the > > bottom as they are pushed deeper into the water, and therefore expand into > > greater width and stability in the higher parts. ...snipped...[snip] > > Philip's and Leander's comments remind me of something interesting about > the way a sponsoned folding kayak behaves when it has taken on a lot of > water. If you turn that folding kayak on its side, it will rise on the > sponson on that side and spill a lot of the water out, up to about the > inside level of the sponson. (It is a neat way to begin partial > emptying of a folding kayak that most people don't know about. The > phenomenon is even more pronounced if you also have flotation bags fore > and aft as you alway should in any folding kayak or non-bulheaded > kayak.) > > If there were no different in the displacement effect between a > hardshell and a folding kayak with sponsons, then this float-up > phenomenon would also happen with a hardshell laid on its side. To my > knowledge, the hardshell would not at all rise that way to spill out the > water, only the sponsoned kayak would. That column of compressed air in > the sponson is fighting its way to the surface. Ralph, this is completely accurate to this point. The [emphasized] part of your next sentence (see below) describes an effect which is not physically possible until the inflated tube is **completely** submerged, thereby displacing a volume of water equal to the sponson's volume, giving a buoyant effect equal to the weight of the water displaced. Any restoring force, as Philip points out, which acts to right the kayak, *before* the sponson is *completely* surrounded with water (both inside and outside the yak), is due to the *form* of the outside of the yak, and can not be affected by what is inside the yak. OTOH, I think Philip may have correctly identified the source of the "feeling" you and he describe -- it is due to local deformation of the *outside* of the yak's surface, owing to the flexible character of the hull. > In a corollary way, **it also resists being submerged.** [emphasis added] > Philip's idea of a dynamic as opposed to > static displacement certainly has a ring to it that shows itself in real life. Yes. The *dynamic effect* could be genuine. The "resists being submerged" can not. I love my folding boat, but it can not violate principles of physics or buoyancy. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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