> From: "Evan Dallas" > Subject: [Paddlewise] Kayak speed vs length > > I've often heard (and intuitively accept) that all other factors being equal, a > longer kayak will be faster than a shorter one. I've got a friend who disagrees > with this, but I've had a hard time explaining why this would be true. > A longer kayak isn't faster for a given energy input, but it has a higher "hull speed"- that is, a speed that cannot be exceeded without more adding energy than is available. There's a nice description at http://www.dt.navy.mil/ip/mfp/paper11.html, the guts of which is this: As a boat travels through the water it generates waves. This is because the boat displaces a volume of water and that water has to go somewhere. At low speeds the boat spans over multiple waves. As the boat speeds up, the length of the waves increases and the boat eventually finds itself in a trough with a length equal to the boat's waterline. This happens at a speed equal to (in knots) around 1.34x the waterline length (LWL) in feet. At this speed the drag on the boat from these waves is minimal. As the boat tries to go faster than this "hull speed", the wavelength doesn't increase. It can't because it can't get any longer than the LWL of the boat. Instead, the boat tries to pass the wave, and to do so, it has to climb the crest of the wave in front of it. This takes a lot of energy. (If the boat has enough energy to do so, it goes up on plane, stops making waves and drag drops drastically) So any relatively low powered craft, like a kayak, has a sort of terminal velocity- a speed at which it takes more energy than a paddler has available to exceed- and that speed is mainly a function of LWL. -- mike ------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org http://www.findascope.com *************************************************************************** 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/ ***************************************************************************
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:33:22 PDT