Joined: Feb. 2006
||Posted: Mar. 05 2006,13:01
Actually, I read all the posts in this thread (and in paddle threads 1-4), and I don't disagree with Broze at all. I was trying to explain his conclusions in terms of basic physics, rather than focus on the subjective items he discusses. Clearly, there is enough complexity in paddling (in fact, in any human/machine interaction) that simple physics may not give the correct answer, but in this case it gives THE SAME answer as Broze reaches. I was trying to get the discussion to focus on work (force and distance) and away from the fuzzy ideas of paddle speed through the water, etc. My conclusion, restated, is that for any paddle craft there is an optimum blade size which minimizes the total energy loss, from blade slip, wind load on the top blade, and swing effort. My personal conclusion is that for actual paddle craft, that minimum loss occurs with a fairly small blade, and anything larger is wasted.
But recognize that Broze's discussion is biased toward racing kayaks: he wants to minimize energy loss and maximize boat speed in a situation where the boat is a) very low resistance, and b) already up to speed. (The start of an ocean race takes a few seconds out of a total time that mey he measured in hours.) Look at a very different situation, a white-water paddler, where the paddler takes relatively few strokes, and relies on each one to put the boat where he needs it to be. In that case, the paddler applies high effort to each stroke, and wants to minimize slip. Thus he optimally uses a much bigger blade than the tourist or the ocean racer. This type of experience is probably what prompts many kayakers to buy huge blades: the huge blade gives great "grip" even starting from rest. The decision that a smaller blade works better seems to take time and experience to reach, hence the value of Broze's article.
Somewhere in this discussion I seem to recall a brief mention of the effort that is required to turn the blade in the water; that is, the blade goes in more or less vertically, and is lifted out with a backwards tilt, so turning the blade in the water is wasted effort. I don't mean twist around the paddle shaft axis; I mean rotation around a transverse axis across the hull waterline. That energy loss is larger for a long, slender blade than for a short, wide blade of the same area. I've never paddled a wing blade, but suspect from watching them in action that they capture some of this otherwise lost energy.
Another factor not addressed by this simple physics analysis is that a larger blade also increases side forces on the top blade that can upset the paddler in crosswinds, thus pushing the sea kayaker to prefer the smaller blade even if it meant some loss of efficiency.