My last email missed an important point. Although I haven't seen a Klepper expedition sponson deform when held under water, it probably would deform when hit with a solid wave and the impulse response might be considerably damped. Thus could the energy absorbtion of waves pounding into a deformable skin and sponson (like bullets into wadding) render the kayak more stable? PeterO *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
In a message dated 4/9/99 12:17:56 PM Pacific Daylight Time, skerries_at_hotmail.com writes: << 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. >> Thanks Philip. Your explanation of what could cause the effect others have felt provides the reasonable explanation my prior posts were requesting. Many claims are made for skin boats and folders, without proof or even a believable hypothesis to back them. Your hypothesis provides something concrete to discuss, conjecture over, and even test. Now, to get the Khatsalano out and see if I can feel the effect you describe. . . . Harold *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
(SNIP) >> > >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] One can always build a rigid boat with the same shape as the folding boat in its distorted condition. Granted the distortion can vary with inflation so perhaps some variable flotation and consequently stability can occur but I have seen nothing but subjective commentary on this. A wise person would like to see stability tests on this before endorsing it as a good idea rather than folding kayak zealots trying to find unnecessary justification for their investments. Folders have enough going for them without trying to bestow divinity upon them. >> >> 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.) In this case the integral buoyancy tanks. (The word "sponsons" lacks precision. If you mention sponsons to a naval architect he pictures external appendages projecting away from the hull surface. I despair of paddlers ever learning appropriate nomenclature.) act in a similar way to the pods and sea socks of some of the more thoughtfully built rigid kayaks. These boats empty in exactly the same way. Many paddlers achieve this result by packing their boats with waterproof bags along the interior sides of their rigid boats. The sponsons do not cause the boat to "rise on its side". It simply floats high according to its volume, shape, and any sealed internal chambers. >> 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. Unfortunately (or fortunately if you design ships and boats) Archimedes disagrees. The righting moment does not vary with how the volume is obtained but with the shape of the immersed portion and the amount and distribution of flotation. Air, being somewhat stupid, cannot tell up from down nor does it behave differently when in a bag, a rigid tank, cells of closed cell foam, empty (but sealed) water bottles, empty (but recorked) bottles of Pinot Noir etc. >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. I agree that soft folders do "feel" different. I suppose some, like me, might not like the feel. I likened it to paddling a bowl of jello. I prefer my folders set up as rigidly as possible. But then, ...... > >> 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. Since displacement remains constant except in dynamic conditions (waves etc) when it varies regardless of the hull construction, I think the terminology inappropriate. I think the term "variable form" more appropriate. How this variable form affects the stability etc. can have a positive or negative effect depending upon ones objectives and circumstances. I know this sounds like nit picking but the careless use of terms leads to confusion. Berkley Choate wrote; >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. Overconfidence does not appear to apply only to SOT's. No one could accuse the Tsunami Rangers of lacking skills although their confidence certainly exceeds that of most paddlers. SOT's have virtues and to reject those virtues because of their very value seems a bit fatuous. One could just as easily say that kayaks inspire overconfidence and that everyone should paddle canoes because they are open and inspire more fear in the paddler. HMMM better yet, life jackets inspire overconfidence so.......... :-) :-) :-) Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
John Winters wrote: MAJOR SNIPS > exceeds that of most paddlers. SOT's have virtues and to reject those > virtues because of their very value seems a bit fatuous. One could just as > easily say that kayaks inspire overconfidence and that everyone should > paddle canoes because they are open and inspire more fear in the paddler. > HMMM better yet, life jackets inspire overconfidence so.......... > > :-) :-) :-) > > Cheers, > John Winters Why do I get a feeling that this presentation was just a John Winters setup to breathe new life into the lifeless argument about life vests and push the cause of canoes? :-) I do concur on the point made about SOTs, their virtues and the myopia some people display in rejecting them. 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/ ***************************************************************************
-Ralph wrote; > > >Why do I get a feeling that this presentation was just a John Winters >setup to breathe new life into the lifeless argument about life vests >and push the cause of canoes? :-) > No way. I refuse to discuss it further. Just brought it up to show how a little inconsistency goes a long way. :-) Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** 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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