I recall seeing a comment awhile back about a spherical boat having the minimum wetted surface. Something about that statement bothered me, its been bouncing around in the back of my head. A sphere has the minimum surface for a given volume, that is true, However if you add the constraint not of fixed volume, but fixed length at waterline, a sphere no longer is the ideal minimum wetted surface shape. Think of soap films on various wire shapes, they tend toward minimum surface as stretched between shapes. So for a defined length, keel line and top line, you'll get a single film stretch between this outline. Not very practical as a boat, no volume, no displacement... Ok, so you start adding other wire shapes to separate the single film into two films so you get some volume into the kayak. So you start getting two films that flare out to meet the new wires added to achieve the desired beam at various points along the length of the kayak. a skin on frame shape. Hmm So, figure the length you want, and enough volume to fit a human and cargo in, haven't I just defined a skin on frame kayak shape? The shape of the outer elements, ribs, keel, stringers is defined by the builder, and if done properly, the skin is tensioned to provide the minimal wetted surface as constrained by the framework.... dave -- Dave Uebele (daveu_at_sptddog.com) Spotted Dog Systems http://sptddog.com/daveu.html *************************************************************************** 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/ ***************************************************************************
On 5/17/01 10:42 AM, "Dave Uebele" <daveu_at_sptddog.com> wrote: > The shape of the > outer > elements, ribs, keel, stringers is defined by the builder There is the rub. What is the shape of the ribs going to be for minimum wetted surface? The soap film going from rib to rib is easy. It will be essentially a "straight" line. The more complicated question is what is the rib shape going to be. In the absence of other constraints the rib shape will be a hemisphere but generally there are other constraints. ---------- For those that are interested, there is a program for designing kayaks on the marinerkayaks web page that will mathematically create the minimum wetted surface kayak within imposed restraints. The documentation for that program discusses these issues. *************************************************************************** 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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