Numbers

– Last Updated: Aug-28-11 11:37 AM EST –

Length /width ratio do not tell us much about potential hull speed, but is useful in evaluating tracking or directional stability.

The best number to evaluate tracking, course keeping ability, is block co-efficient, Cb. The "block" is WATERLINE length, width and depth. The less of that three dimensional block the hull fills, the better it can be predicted to track.

Since most tandems are loaded 4-5" deep and most solos 3=4" deep, we can simplify tracking estimation by using waterline length/width, or more properly length/beam, ratio. Finer hulls track better than fat ones. Wow! who'da thunk? But, the length/ width number doesn't tell us much if anything about speed. See below

Waterline length is the best indicator of forward speed. Speed is predicted by using the waterline length. The formula is the square root of the length, in feet, multiplied by the speed/length ratio, which runs around 1.55 for mph using feet as units. Longer hulls are faster.

Withing given waterline lengths, more precise speed estimates can be made using prismatic co-efficient, Cp, the prism being the maximum waterline beam and depth as the prism and extending it to waterline length. The cubic area of hull filling that prism yields the

PC.

Winters, in 'the Shape of the Canoe', claims recreational hulls should have PCs in the .51-.55 range, performance boats .60 to .62 Lazauskas in various articles published by University of Adelaide, one with Winters, and in Boat design Forums, suggests optimal speed results have somewhat higher Cps. Of note, John Winters Olympic Sprint Kayak had a Cp of .665

Again, L/W doesn't address speed; it is a predictor of tracking. The second most important indicator of tracking is stern rocker. Less of it counters poor forward stroke technique, carrying the blade aft of the body and diagonal rather than vertical paddleshafts, which cause yaw, turning the canoe/kayak off course.