Did I read Peter Chopelas correctly that the ratio of thrust to paddle area was unimportant or, at least the wrong issue? If so I wonder about some things. Suppose we had two paddles one 120 sq. inches and one 80 square inches. both produce the same thrust at the same velocity and the same power input. Does this mean that both paddles are equally efficient or that the difference is unimportant? Can anyone think of any reasons why a smaller paddle that produces as much thrust as a larger paddle might prove advantageous? Also what is one to make of C.A. Marchaj's use of the Driving Force Coefficient ( Equivalent to the Thrust Coefficient or thrust per unit area)? I get the impression from his book 'Sailing Theory and Practice" (See pages 148 to 154) that this has a significant importance where one wants to optimize output from a given input. Cheers John Winters *************************************************************************** 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/ ***************************************************************************
John, First, how about we settle on a physical definition of the term "thrust"? Is it in foot-pounds (e.g., newton-meters), pounds (newtons), or what? I suspect Peter may be using thrust to mean something different from what I understand it to be: a force, which would have to be in pounds or newtons. Secondly, if there were two paddles of differing area, producing the same thrust (force), then the pressure on the surface of the smaller one would have to be greater. That would imply less slippage of water off the surface as the paddle moves though the water (if the paddle is fully stalled). If the paddle is not fully stalled (or nearly so), then it must be producing a force through the infamous "lift," using some variant of Bernoulli's principle. As for Marchaj's use of thrust per unit area, if thrust is truly a force, and the area is sail area (don't have the reference at hand), then basically that means the craft is making more (or better) use of the wind than another craft of similar sail area. In other words, one sail could be a highly refined one and the other could be one that is not. The parallel to a paddle would be a one that provides more rearward thrust for the same "effort" (e.g., force put in) by the paddler. And, this could be achieved by the infamous "lift." -- Dave Kruger Astoria, OR ----- Original Message ----- From: "John Winters" <jdwinters_at_eastlink.ca> > Did I read Peter Chopelas correctly that the ratio of thrust to paddle area > was unimportant or, at least the wrong issue? > > If so I wonder about some things. > > Suppose we had two paddles one 120 sq. inches and one 80 square inches. both > produce the same thrust at the same velocity and the same power input. Does > this mean that both paddles are equally efficient or that the difference is > unimportant? > > Can anyone think of any reasons why a smaller paddle that produces as much > thrust as a larger paddle might prove advantageous? > > Also what is one to make of C.A. Marchaj's use of the Driving Force > Coefficient ( Equivalent to the Thrust Coefficient or thrust per unit area)? > I get the impression from his book 'Sailing Theory and Practice" (See pages > 148 to 154) that this has a significant importance where one wants to > optimize output from a given input. *************************************************************************** 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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