Dear Nick, I most sincerely and humbly apologize to you for the way my last posting came across. It was not my intent to insult you, it was late and I had been at it too long. I was pretty frustrated with my inability to be understood, and I was attempting to point out the error in your statements by showing strong emotion in my statements. I should have been more careful with my words, I have a lot of respect for you and every one else on this list. I never called you any names, or attacked you personally, and it was not my intent to insult you. Please accept my apology in all sincerity. After considering where the communication was not being understood I realized it was one of terminology. In my career as an engineer very precisely defined words are used to ensure proper understanding and it has become so automatic that I simply made statements, and defended them, as if everyone else understood these words the same way. Efficiency is one of these words. It is a word commonly used in casual speech in ways that are improper in engineering. For example I could say "my wife spends our family income with great efficiency", this could be taken two ways: either I was being sarcastic as how fast she spends money, or I was complimenting her on how much value she gets by careful shopping. You would need tone, facial express, body language, etc. (i.e. more information) to know more of what I had in mind, both of which we are deprived of with email. However, neither of these are accurate usage with regards to the engineer's understanding of efficiency. I would never make a statement like that (especially if I want to stay married!) because that is not what efficiency is, and it is very imprecise statement since the meaning could be misunderstood. Another common usage is when talking about fuel economy in automobiles: to say "the Corolla is more efficient than the Mercedes Benz" could be untrue in an engineering sense. The efficiency with which the Mercedes engine converts fuel into mechanical energy could be higher than the Corolla, but because the Mercedes is bigger and heavier it still take more fuel to drive it over a given distance as the Corolla. It would be correct to say that the Corolla has better fuel economy, but it is not necessarily more efficient if you define it as it is in engineering usage. Efficiency as defined the way I used it, as used in engineering, is a ratio of the power output divided by the power input. To know what this means you have to know what "power" is, another one of those words being thrown around and commonly used in everyday speech, but has a very precise technical definition. The popular snack bar called a "Power Bar" for example is a nonsensical label from an engineering point of view (but I would hope that most engineers realize that marketing knows no such limitations). Common units for power are horse power, or watts, or foot-pounds per minute. Power is defined as the work rate. That is the amount of work done over a given amount of time. Work now must also be defined: it is a unit of force applied over a distance, common units are Foot-pounds for example. Force is defined as a mass with an acceleration applied to it, hence Force = mass x acceleration, or F=ma, units of force are pounds or newtons. Note that pounds and kilograms are not equivalent units since pounds is a unit of force and kilograms is a unit of mass. The old English unit of mass is a slug, which would be the English equivalent unit of mass to the metric kilogram. It is just understood generally that a kilogram equals 2.2 pounds of force when the acceleration of 9.8 meter per second (or one standard gravity unit) is applied to it. So I have never argued, as you stated, that X does not equal X. I argued that force, does not equal work, and it does not equal power, and it can not be equated to efficiency in any way. This background is necessary to demonstrate that in order to measure efficiency, the way I was using it, you must have three different measurements: a unit of force, a unit of time, AND a unit of length. To say the paddle that moves slower with the same force (a unit of time and a unit of force only) is more efficient is not possible, you do not have enough information. This is like I ask you how fast you were driving, and you say "12 minutes", and I ask over what distance? And you say that does not matter, all that matters is 12 minutes, all other things being equal. What???? Without more information, 12 minutes is meaningless. Your glider vs. parachute comparison was equally nonsensical without equal basis of comparison. When you make statements like that you indicate to me you are viewing these comparisons in a very confused and imprecise non-technical way. The whole idea of "slippage" when applying a force against a fluid is as equally meaningless, especially when talking about efficiency the way I meant it. If you define slippage as the amount of distance the paddle move backward from a fixed point relative to the water surface during a stroke, you end up with a lineal distance measurement only. Not enough information to determine efficiency at all. I suppose you could redefine it as "slippage efficiency" and use that as a criteria. But it would not be related to power consumption at all. By this definition than the largest paddle you can get would have the least slippage, and be the most "slippage" efficient. But clearly this is not true with regards to power consumption. Slippage is a nonsensical way to even think of the way a paddle works anyway. You can not apply a force against a fluid without "slippage", it would not be a fluid by definition. Even just comparing the paddle movement in water to pushing against a solid object like concrete is too alien for someone who understands fluid mechanics to think about, fluids do not act that way. This is like saying a 624 LB boat will displace 10 cubic feet of fresh water (62.4 LB/cu. ft.), 9.75 cubic feet of sea water (64 LB/cu.ft.), and ZERO cubic in cured concrete. It is not comparable, that is a nonsensical statement. [In case you were wondering, it would be about 4 cubic feet in liquid concrete]. And when I consider a touring paddle for sea kayaking I would primarily want to consider total power consumption over a given distance. That is what matters most for sea kayak touring. For white water or surf kayaking the requirements, and the paddle design, would be totally different. As different as the hull requirements I would imagine. Though I am almost totally ignorant of what is necessary for WW kayak paddles, all I know about it is what I have seen on TV. I would think a native style paddle for surfing or WW use would be a big mistake, but I could not tell you since I have never experienced it. So speed or cadence of your paddle stroke is not relevant to power consumption nor efficiency in sea kayaking. Neither is "slippage", neither is the size of the blade, nor the length of the shaft. For true efficiency, the way I meant it, the "power-in" is the work rate (say in Foot-pounds per minute) done by the paddler necessary to maintain a given hull speed, the "power-out" is the force required to overcome the drag on the hull (in pounds) at a given speed (feet per minute). Hence the total units for both would be foot pounds per minute, and you get a dimensionless quality when you divide power-out by power-in, and efficiency is always going to be a number less than one, or in a percentage. That is what I meant when I said the high aspect ratio paddle is more efficient for sea kayaking than the low aspect ratio "Euro" paddles. The high aspect ratio paddle will use less power (fewer calories) traveling the same distance at the same speed. And that is a fact of fluid mechanics, not a theory or an opinion. If you optimize the foil shape for a high aspect ratio paddle blade, and developed the optimum stoke mechanics to take advantage of it, and you do the same with a low aspect ratio plan form, the high aspect ratio paddle will consume less power going the same speed. There is no way around it, it is a fact of physics, not my opinion, nor just a theory. A hard fact you can not change. There are complex but very well known scientific reasons for this. I will not bore anyone with the details, but they are available for anyone to look up for themselves. Also note that the same paddle design that is most efficient for touring would not be the best for racing. Racing is not concerned with minimum power consumption at touring speeds, but rather in getting maximum speed out of the power available. For that you need a different blade and very different stoke mechanics. So never compare racing technique or racing paddles with touring, they are attempting to optimize different qualities. All of my statements were directed at explaining this, and my words were very precisely used, as were all my descriptions of your postings. None were ever meant to be taken as insults (though they were expressions of my frustration). Note that even calling your posting nonsensical or ignorant were not meant in a pejorative way, I used the term ignorant about myself above when describing things I know little about. Accurately defined "ignorant" is not the same as stupid. I do not use it that way and I did not intend you to take it that way. This just demonstrates how important it is that everyone use words the same way, otherwise you can not communicate. It is especially unfortunate that recent trends have been to use fancy words improperly because it makes speech or prose appear more sophisticated. It is one of my pet peeves, and really demonstrates lack of language skills, not sophistication. But it also leads to many unknowingly using words like "efficiency", "power", and "force" in inaccurate ways, and not to understand what these words really mean. All the best. Peter Chopelas *************************************************************************** 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/ ***************************************************************************
"Peter A. Chopelas" wrote: } Subject: [Paddlewise] Apology for post about paddle efficiency > > This background is necessary to demonstrate that in order to measure > efficiency, the way I was using it, you must have three different > measurements: a unit of force, a unit of time, AND a unit of length. To > say the paddle that moves slower with the same force (a unit of time and a > unit of force only) is more efficient is not possible, you do not have > enough information. "slower" to me means velocity, not time. A unit of velocity is a combined unit of length and time. So "slower with the same force" is a unit of *velocity*, and a unit of force, which is a unit of power. Try dimensional analysis for a moment. > The whole idea of "slippage" when applying a force against a fluid is as > equally meaningless, especially when talking about efficiency the way I > meant it. If you define slippage as the amount of distance the paddle move > backward from a fixed point relative to the water surface during a stroke, > you end up with a lineal distance measurement only. No, it's a velocity. How *fast* the paddle slips backward. And that mkes it power. > Not enough information > to determine efficiency at all. I suppose you could redefine it as > "slippage efficiency" and use that as a criteria. But it would not be > related to power consumption at all. By this definition than the largest > paddle you can get would have the least slippage, and be the most > "slippage" efficient. But clearly this is not true with regards to power > consumption. This IS true. Don't just say "clearly this is not true". Since you're clearly not interested in hearing this from me, try reviewing this web page: http://www-atm.atm.ox.ac.uk/rowing/basics.html#section3 > Slippage is a nonsensical way to even think of the way a paddle works > anyway. You can not apply a force against a fluid without "slippage", it > would not be a fluid by definition. Of course you always have slippage, but that does not mean you can't minimize it. > way, otherwise you can not communicate. It is especially unfortunate that > recent trends have been to use fancy words improperly because it makes > speech or prose appear more sophisticated. It is one of my pet peeves, and > really demonstrates lack of language skills, not sophistication. But it > also leads to many unknowingly using words like "efficiency", "power", and > "force" in inaccurate ways, and not to understand what these words really > mean. A remarkable statement from someone who claims that "slower" implies a unit of time, with no length component. *************************************************************************** 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/ ***************************************************************************
At 1:54 AM -0700 5/20/01, Peter A. Chopelas wrote: >Dear Nick, > >I most sincerely and humbly apologize to you for the way my last posting >came across. <snip> Apology accepted. ><Snip> > >Another common usage is when talking about fuel economy in automobiles: to >say "the Corolla is more efficient than the Mercedes Benz" could be untrue >in an engineering sense. The efficiency with which the Mercedes engine >converts fuel into mechanical energy could be higher than the Corolla, but >because the Mercedes is bigger and heavier it still take more fuel to drive >it over a given distance as the Corolla. It would be correct to say that >the Corolla has better fuel economy, but it is not necessarily more >efficient if you define it as it is in engineering usage. I am trying to look at just the "efficiency" of the paddle itself, as one would look at the efficiency of a car tire. Some tires are more efficient at transferring propulsion between the road and the car. Any tire can be used in a more or less efficient manner due to the engine's power output or driver's skill, but it is still possible to isolate the tire. I have tried to isolate my comments to just the paddle. The efficiency of the whole kayak "system" is much easier for me to analyze if I look at each part separately. The efficiency of engine (human physiology) and the driver's (paddler's) skill are important. But trying to address them all at once is just too complicated for me. By knowing as much about how each works, I can try to make them work together in the most efficient manner. If I choose to. My comments have been made in the light of this effort - looking at the paddle alone. And with that in mind I that my comments apply to all paddles regardless of the generic shape. Nick -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** 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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