For any hull type, theoretical hull speed is only theoretical, not a law. The shape of the hull, especially the length to beam ratio has everything to do with how much theoretical hull speed applies. Or said another way, hull shape and length to beam ratio determine how steep the power/speed curve is at theoretical hull speed.
Tugboats really are displacement vessels, with a very steep rise in power needed when they approach hull speed. So steep, that they will push up huge bow waves instead of climbing onto a plane.
Multihull sailboats, like trimarans or catamarans, on the other hand, have very narrow hulls (at the waterline) for their length, and have only a nominal rise in power needed when they approach hull speed. Often so nominal that there is no noticeable difference in how the hull interacts with the water as hull speed is approached and then exceeded. There is even an argument that above hull speed, these hulls are not really planing, but so what? They go fast with not much energy required.
My understand is that semi-planing hulls trade some hull lift for a softer, more comfortable ride and better handling in rough conditions, but are still based on a lower length to beam ratio.
I noticed the Wye Island challenge entrance categories all mention limits for length to beam ratio.
(Can you tell I like skinny boats?)
Posted by: cpcanoesailor@yahoo.ca
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