John Winters wrote ( in another thread): > >Scott provides for us a good example of one attitude towards paddling which >involves expanding skills and constantly pushing ones limits. Another >attitude would embrace a different approach - that of treating paddling as >a means to explore the world. Exploration need not involve pushing one to >the limit. Within the context of my paddling, avoiding a capsize >constitutes the objective of seamanship. To that end I would prefer a boat >that resisted capsize. > >What I wondered, however, was whether an easy to capsize boat could be >defined as a better boat simply because it might be easy to capsize. Is a >Nordkapp a better boat than, for example, a Current Designs Solstice by >virtue of its being less stable? > It seems to me that there are 3 kinds of stability that are more or less independent of each other. Roll stability determines how comfortable you are sitting still in choppy conditions. Down wave directional stability is how well your stern resists skittering back and forth in confused following seas. Wind directional stability determines how easy it is to hold direction in cross wind. I share your preference for a boat that provides some resistance to capsize. Not having wind directional stability, ie. strong weathercocking, is something I dislike greatly. However, it leads to extra work rather than to upset. Roll instability can lead to capsize, especially if accompanied by lack of attention or carelessness. But down wave directional instability can be scary. I have been in some boats that felt truly fine in windy choppy conditions, until I turned down wind. I have been told that a "double ender", with fine entry and exit hull shape, is a term for a sailboat that handles down weather easily. Does the same apply to kayaks? Jerry *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Gerald Foodman wrote: > > [snip] But down wave directional instability > can be scary. I have been in some boats that felt truly fine in windy > choppy conditions, until I turned down wind. > > I have been told that a "double ender", with fine entry and exit hull shape, > is a term for a sailboat that handles down weather easily. Does the same > apply to kayaks? Could be, but any hull will have some directional instability down wave, *until it begins to surf on the wave.* Then the stability normally increases, though most sea kayak hulls (I think) will not be stable straight down the wave. Rather, they will be stable to the left (or right), as you force a chine to carve on the wave. The directional instability comes (in part) from the differences in speed of the water in the wave. Check out Bascom's "Waves and Beaches" for a description of water motion within a wave. -- 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/ ***************************************************************************
Jerry wrote; >I share your preference for a boat that provides some resistance to >capsize. Not having wind directional stability, ie. strong weathercocking, >is something I dislike greatly. However, it leads to extra work rather than >to upset. Roll instability can lead to capsize, especially if accompanied >by lack of attention or carelessness. But down wave directional instability >can be scary. I have been in some boats that felt truly fine in windy >choppy conditions, until I turned down wind. > >I have been told that a "double ender", with fine entry and exit hull shape, >is a term for a sailboat that handles down weather easily. Does the same >apply to kayaks? I believe this to be valid in comparison with wide sterned power and sail boats. The wider sterns are more affected by the following seas and tend to increase the chances of broaching. However, this "rule" commonly applied to power and sail boats may not be strictly applicable to light boats like kayaks that lack draft and can be accelerated so easily. Kayaks and canoes use a superior steering system unhampered by being at the stern and having the slow response of larger heavier boats. Of course, the term "fine" can present problems. The Chinook that has very fine ends (relative to many boats) seems to broach easily (my experience and that of some others). The balance between fine and full presents a huge challenge. When the designer gets it right he probably deserves sainthood. On the negative side, kayaks operate in "heavy" seas most of the time (relative to ships) and that means constant attention. When the wave length equals (aprox.) the boat length and the midsection is in the trough the narrower ends must support the boat and provide stability. Despite the apparent gravity increase in the trough there can still be a loss of righting arm and, consequently, righting moment. The "on site" problem for paddlers is whether to slow down or to speed up to avoid broaching. Marchaj discusses this in his book "Seaworthiness: The Forgotten Factor and I suspect his thoughts might apply to kayaks more than sailboats due to the relatively heavy seas we paddle in. Dave Kruger correctly mentioned the directional instability down wave as being due to the water particle motions in the wave. The trick from a design standpoint will be to minimise the relative effects. For instance. One can increase buoyancy and reduce draft forward to reduce the effect of plunging the bow into the back of the wave. As Dave points out, you can also use the shape of the boat to control its direction while surfing. When travelling slower than the wave in serious conditions a sea anchor can be used to keep the boat normal to the waves. For non traumatic conditions the usual braces etc. work fine. 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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