At 12:36 PM -0700 5/15/01, Peter A. Chopelas wrote: > Nick Schade wrote: >> More apparent slippage is inefficient...."Slippage" is an indication that >you are >> accelerating water and thus wasting energy. > >Your first statement is meaningless, how can you say more slippage is >inefficient? Did you ever measure it? How? You are making unwarranted >assumptions. What is slippage anyway? (not the 'feel' but something >measurable). So it depends on how you measure "slippage"...either it is >all slippage, or none of it is. > >The word "slippage" is meaningless unless you define it, and depending how >you define it it could mean almost anything. It is best to avoid such vague words. > We have a working definition of the paddle moving backwards through the water. I don't see this a being particularly vague. For the paddle to move backwards, water must also move. There are other ways of making the water move such as vortices. But however you make your boat move, you do it by moving water. The more water you move the better. The slower it moves, the better. We can drop the term "slippage" if it makes you more comfortable. > > >> As long as you move the paddle parallel to the direction of motion >> desired all the force applied will go directly to propelling the >> boat. > >This is totally false and again based on uninformed intuitive ideas. Is it really? Please re read it. Any force you apply parallel to the motion of the boat will be useful for moving the boat in that direction. Are you suggesting that forces don't create reactions in the direction they are applied? I know you are suggesting that I don't know that you can make forces parallel to the direction of boat motion while moving the paddle perpendicularly. I am aware that you can, but in a paddle stroke most of the force comes from the fore-aft motion of the paddle, with the perpendicular motion serving only to increase the efficiency somewhat. The increase in efficiency is not insignificant, but it does not materially change my point. If you can increase the amount of water you move without increasing the velocity at which you move it, you will be more efficient. By slicing the blade through the water perpendicular to the water you will always be pushing against stationary water so you will be not be accelerating any given mass of water to as high a speed. As a result you move a larger mass of water more slowly. This is more efficient and is often worth the energy required to move the paddle sideways. Even native paddles get most of their power from fore-aft motion, but a slicing motion to the side helps as it does euro paddles. > > It does not matter how the force is created: drag, friction, >> turbulence, lift, whatever. The only time there is wasted force is > > when there is a component of motion perpendicular to the direction of > > propulsion, then all the same things - drag, friction, turbulence, > > lift, whatever - are bad things. The only useful force is one >> propelling you in the direction you want to go and it doesn't matter >> how you create it. > >this is true, but remember the vortex? you get lots of fluid movement but >most of it cancel itself, that is why they are so wasteful of your efforts. > The theoretically most efficient thrust you can generate will have no >vortexes (which is impossible in the real world), and convert all your >effort into forward thrust (also impossible), how you move the paddle is >not even important since it will vary with the type of paddle you are >using. Once the fluid is set in motion it makes absolutely no difference what it does. The momentum has been applied and has been conserved by the resulting reaction of the boat. How that momentum dissipates itself in the water is irrelevant. It would be cool if you could recapture the momentum, but as a practical matter you can't. The bottom line is it doesn't matter what the vortices do once you made them, the fact that you made them is what is creating the power. The vortices and other water motion are the source of your momentum. If you can make the vortices bigger and slower, you will be more efficient than if you make them small and fast moving. If the vortices cancel perfectly, then no momentum was applied to the water and the boat received no momentum. The goal remains the same, move as large a mass as slowly as possible for the greatest efficiency. > >Take the extremes: An ice cream scoop type paddle would probably be best >pulling strait back, linearly accelerating the fluid. But the other >extreme, a paddle that looked like an airplane propeller, would be best >used by sweeping it through the water in an arc, and WAY more efficient >than the ice-cream scoop paddle--hence the native style paddle. Imagine a parachute and a glider. Hold each 100 feet off the ground and let go. The glider will hit first. While it is capable of creating a lot more lift you must first apply a lot of kinetic energy before it will fly. It will take longer to drop only if you get it going real fast. So which is more efficient? The glider may stay up longer if you give it more height to build up speed, but it will be a close call. The glider can seek out thermals so it has an advantage over a parachute, but a parachute is very efficient and the bigger it is, the more efficient it will be. By giving the parachute a little bit of forward motion so it acts like a wing it can become even more efficient. Having a paddle work like a wing will indeed increase its efficiency but any paddle can work like a wing. Increasing it's aspect ratio helps when it is used as a wing, and so will increasing the blade area. > >> >> <snip> >> efficient. It will require fewer strokes to maintain the same speed. > >There is your inaccurate assumptions showing themselves again; this is >false. I have measured this before on a human dynamometer. The number of >strokes it takes to maintain the same speed is not related to how much >energy out put you are producing. The 10-speed bike analogy makes this >clear, peddling slow and hard in high gear, or fast and easy in low gear, >could mean you are expending exactly the same amount of energy. However, >with the human "machine" there is an optimum speed for the same output of >energy to minimize input (this is actually true with most machinery). > Generally the low gear (higher speed, less force) IS MORE EFFICENT with the human body. You are confusing human efficiency with paddle efficiency. I agree completely that the human body works best apply small amount of force quickly. But given that, when applying the force it is better to move a large mass slowly. One form of efficiency is physiological one is physical. These two forms of efficiency are not incompatible. For example a short, quick stroke does not end up moving the water very fast, but it moves a lot of water because you can get in more strokes in a given amount of time. This kind of stroke is efficient for the body to output power and efficient for the paddle transferring the power to the boat. > >> >> It does not take any knowledge of fluid dynamics to understand this, >> and no amount of fluid analysis will change it. >> > >This may be true, but it is clear from your arguments you still have a lot >to learn. Why don't you just go out and learn the native paddle technique >and try it,? You do not need to know anything about fluid mechanics to >know which works best, but you are at a clear disadvantage if you put forth >technical arguments about things you do not understand, and without the >knowledge of actually trying it out. I contend IF you use PROPER >technique, you will know how much better native paddles are. I'm sorry that you think the only way for me to learn fluid dynamics is to learn how paddle. I find it unfortunate that advocates of native techniques must always resort to "if you don't like it, it must be because you are doing it wrong". Even I could come up with much better arguments in favor of native paddles than that. In fact all of my arguments work just as well for native paddles as Euro style paddles. The paddles are really not all that different, they can and do interact with water via the same physical mechanism. >So if you want to scoop ice-cream, or shovel manure (as it appears many on >this list are in the habit of doing), use your Euro blades, for efficient >paddling you need a high aspect ratio paddle. There is no way around it. > Do not argue, it is a FACT of any fluid machinery. You can go look this >up for your self in any fluid mechanics textbook if you are so enchained >(check out aspect ratio, propeller design, etc.), but do not put forth such >statements until you have done so. Short of that you will either have to >take the word of people who do know, or just go out and try it! Let us assume that the only difference between a euro paddle and a native paddle is aspect ratio (blade area, and foil shape are the same). One of my books on aerodynamics says: "From a pure drag standpoint, the larger the span can be, the better the airplane designs will be. However, a large span means larger bending moments in the wing structure because the lift loads are acting farther from the root of the wing. Furthermore, a large span with a fixed area means shorter wing chords all along the span and, therefore thinner wings. The wing acts as a beam, and a shallow beam requires heavier material on the top and bottom of the structure to with stand a given bending moment. Thus a high-aspect-ratio wing has a heavier structure..." (Fundamentals of Flight, 2nd addition, Richard Shevell, (c) 1989, Page 188) So higher aspect ratio is better if the paddle is used like a wing, but there are trade offs for a high aspect ratio wing. It needs to be heavier to be as strong as a low aspect ratio wing. If the area is the same, it needs to be thinner. But if it is thinner, it needs to be even heavier to be as strong. If it is not thinner it will have more drag. But everything else being equal a high-aspect-ratio paddle will be more efficient when used as a wing. However: - Everything else being equal the paddle with the largest blade area will be the most efficient. - Everything else being equal the lightest paddle will be the most efficient. - Everything else being equal the fastest cadence will be the most efficient. - Everything else being equal the boat with the strongest paddler will be the fastest. - Everything else being equal the paddler with the best technique will be the fastest. Wouldn't it be nice if you could keep everything else equal. Unfortunately, if you change one thing, something else is bound to change. In reality foil shape (or the cross-sectional shape of the blade) is not the same between euro and native paddles. And the effective blade area is typically different as well. So comparing only aspect ratio is not valid. You must also look at blade area, width, length, thickness, shape, weight, strength and other aspects of how the paddle is used in the water. A favorable aspect ratio is not enough to assure efficiency. Generally native paddles are made relatively thick and this lets them be light weight and still strong. Native paddles are too thick to be compared with euro paddles by aspect ratio alone. Their thickness cuts back on their achievable efficiency when used like a wing. However, being thick and light weight are two of the best qualities of a native paddles. Why lightweight is good is obvious. Being thick makes them much less dependant on good alignment and position when rolling and sculling because they are less likely to stall. It also makes them less touchy about the angle when using them like a wing in a forward stoke. A thinner blade will be more likely to lose efficiency if it is held at too steep an angle. So you can gain some efficiency with a native paddle because it is less reliant on good technique. There are good reasons to use a native style paddle. They do not need to be the optimum paddle for forward paddling efficiency to be good. I find it kind of silly that any comment even vaguely hinting that native paddles are not the absolute best at everything always draws some kind of impassioned defense that typically devolves into questions of the "critic's" competence. I personally think they can be darned good paddles even if they are not necessarily the most efficient at one aspect of paddling. Why must they be the best at everything to be worth using? -- 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. 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