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. > > 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. A propeller on a boat or aircraft moves exactly perpendicular to the direction of travel yet fairly efficiently provides all the forward motion. you can do the same thing with a paddle in a sculling type stroke, providing forward motion without any movement of the paddle in the direction of travel. You could also have a shape on the blade the provides very little forward motion even though you are pulling parallel to the hull. [and do not argue that propellers are different, both paddles and propellers are fluid machinery and operate on the same principle, one is just optimized for a different type of movement]. Paddle wheel boats move parallel to the line of travel, but why do you think they are not used commercially? They are very wasteful and inefficient. 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. 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. Do not forget that there are a lot of other demands we put on a paddle besides forward motion. And the propeller blade vs. the ice-cream scoop will have to be used very differently to meet these different demands, some better than others, and some requiring more skill and practice. But overall it is my observation that the native paddles and techniques are superior. JUST GO TRY IT! (but learn to use it properly first!). Perhaps the ice-cream scoop is more easily learned, and proper technique is more obvious to the beginning paddler or in rental fleets. But that is no reason for all who hope to become experienced and skilled paddlers to use it. It would be like never graduating from a tricycle or training wheels to a two wheeler. You never experience the full advantage and benefit of the sport with such a severe handicap because you are forced to use inefficient techniques and poorly designed equipment. > > <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. So by your analogy, you should ride a bike in high gear all the time regardless of the road conditions, speed or slope, to be most efficient and expend less energy. This is clearly not true, you end up wasting a lot of effort and energy doing this. Fortunately water is level, but you still have to deal with wind and surface conditions (as you do with a bicycle). > > 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. If you think of the forces on the paddle surfaces as high and low pressure areas (rather than moving fluid, which is actually what causes the high and low pressures, but in very complex ways) to create the forward movement you want, it become easier to understand. with a propeller shaped blade (i.e. native paddle blade) you make your stroke a downward slicing arc movement, kind of like a quarter turn of a propeller (but also pulling back at the same time with your body), you get a very efficient stoke that is also easy on your body. You can not do this with a "Euro" paddle. You also learn real quickly that you get little resistance against the paddle for rolls or braces unless you have some lateral movement of the blade through the water. And it is much less effort to create, and the amount of power you can generate is much larger on the high aspect ratio blades than with the "ice-cream" scoop Euro blades. This is why you must learn proper technique to get it to work, and it has to become automatic. 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! 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. 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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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I don't like appeals to authority but I do have one question that kind of appeals to authority. If Greenland style paddles are so efficient why is it that no Olympic Racers that I have ever heard of (even pre-wing) have ever used them or even a lightweight high tech high aspect-ratio version of them. Did they just completely miss the boat on this because of the wrong assumption that bigger and wider was more powerful? I probably haven't given Greenland paddles enough of a chance to have learned how to use them the most efficiently. I guess maybe I just don't like having wet hands from no drip rings all the time and switched to feathered (by cutting my paddle in two and twisting it 90 degrees before duct taping it back together over a sleeve) like a weenie as soon as the wind blew a little in my face. However, my observations from using them and also sprinting against a paddler equally as strong as myself (at least when he was using the same model paddle as me) who was also very into native paddles and their correct use, was that they were slow on acceleration and couldn't keep up the same top speed. For other uses they seemed just fine (although some like the "Quill" zigzagged around so much in the water under a load they were hard to control. The falling leaf effects flutter rate is higher on a narrower blade. The wing type stroke pretty much relieves this flutter problem though which is one of the reasons I use that stroke even though I don't like wing paddles for cruising for many reasons other than efficiency. Matt Broze http://www.marinerkayaks.com *************************************************************************** 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/ ***************************************************************************
Not an authority, but an ex-engineer... We haven't defined efficiency. In any case, more energy converted to forward momentum per unit energy expended translates to faster speeds. Faster speed does not necessarily mean higher efficiency. If I were a racer, I wouldn't care about how much energy I saved after the race. I want to finish 2% faster, even if I expend 20% more energy. If I were on a multiple all day open ocean crossings, I sure would care about about conserving 20% of my energy and could care less about going 2% faster. I believe Greenland paddles achieve this, primarily through the difference in Reynolds numbers of Air and water. live long and paddle, albert > I don't like appeals to authority but I do have one question that kind of > appeals to authority. If Greenland style paddles are so efficient why is it > that no Olympic Racers that I have ever heard of (even pre-wing) have ever > used them or even a lightweight high tech high aspect-ratio version of them. > Did they just completely miss the boat on this because of the wrong > assumption that bigger and wider was more powerful? I probably haven't given > Greenland paddles enough of a chance to have learned how to use them the > most efficiently. I guess maybe I just don't like having wet hands from no > drip rings all the time and switched to feathered (by cutting my paddle in > two and twisting it 90 degrees before duct taping it back together over a > sleeve) like a weenie as soon as the wind blew a little in my face. However, > my observations from using them and also sprinting against a paddler equally > as strong as myself (at least when he was using the same model paddle as me) > who was also very into native paddles and their correct use, was that they > were slow on acceleration and couldn't keep up the same top speed. For other > uses they seemed just fine (although some like the "Quill" zigzagged around > so much in the water under a load they were hard to control. The falling > leaf effects flutter rate is higher on a narrower blade. The wing type > stroke pretty much relieves this flutter problem though which is one of the > reasons I use that stroke even though I don't like wing paddles for cruising > for many reasons other than efficiency. > > Matt Broze > http://www.marinerkayaks.com > > > *************************************************************************** > 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/ > *************************************************************************** *************************************************************************** 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/ ***************************************************************************
Since both equal racers will be willing to expend all the energy at their disposal to win, the one who through technique or equipment most efficiently transfers that energy to the water in a manner that propels the kayak in the desired direction with the least added drag will be the winner. why can't the Greenland paddle do that as well as you claim it works at slower speeds. I agree with James Tibensky, who said the most efficient paddle is the canoe paddle for covering long distances. Verlen Kruger and Steve Landick will back me up on this one too. Steve told me he found it far more efficient at using the minimum effort to move his very kayak like craft (ultimately 28,000 miles--but less than 1/2 that when I paddled with them and asked the question). While Steve carried a kayak paddle as a spare and to use in rough water he made miles with his light bent shafted canoe paddle and the canoe racers quick choppy little torso rotating stroke. I suspect much of the efficiency gain was in not having to lift the opposite paddle blade up with each stroke and the high stroke rate that maintains a more even speed since the craft doesn't slow as much between strokes and therefore have to be accelerated as much to get it back up to speed. I think Nick is right about this when he says: "-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." I think this is especially true if you take the human out of the system and run it mechanically to avoid human limitations. I would define "efficiency as wastes the least energy". Matt Broze http://www.marinerkayaks.com > -----Original Message----- > From: Albert Wang [mailto:albertwang1_at_home.com] > Sent: Thursday, May 17, 2001 1:55 AM > To: Matt Broze; Paddlewise > Subject: Re: [Paddlewise] paddle sizing and Technology guides design > > > > Not an authority, but an ex-engineer... > > We haven't defined efficiency. > > In any case, more energy converted to forward momentum per unit energy > expended translates to faster speeds. > > Faster speed does not necessarily mean higher efficiency. > > If I were a racer, I wouldn't care about how much energy I saved after the > race. I want to finish 2% faster, even if I expend 20% more energy. > > If I were on a multiple all day open ocean crossings, I sure would care > about about conserving 20% of my energy and could care less about going 2% > faster. > > I believe Greenland paddles achieve this, primarily through the difference > in Reynolds numbers of Air and water. > > live long and paddle, > > albert > > > *************************************************************************** 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/ ***************************************************************************
Hi all, I am using Greenland paddles for about 12 years now but I am only an occasional paddler. I have got the impression, small-blade-ultralight-carbon-spoon-paddles made me faster (yes, I tried them and found them impressive), but here is why I stick to the 'fence-plank': 1. Looks much cooler, nobody would ever think I am paddling twice a year 2. For stabilizing the kayak during a rest, I put the paddle under the deck-straps, using it as an outrigger. This is very efficient with proper deck-layout, my kayaks are about 48 cm beam at the waterline and it's not very cool capsizing while putting your jacket on or off. 3. Easy and fun to build them in my workshop 4. Better control while capsized and preparing for a roll 5. Less power on your wrists per stroke. 6. I like the high stroke cadence for stabilizing while paddling (you also could have used a less tippier boat :-) ) Disadvantages: Labour intensive while surfing, bracing requires a lot of paddle movement Cheers Gerald *************************************************************************** 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/ ***************************************************************************
Nick Schade wrote: > > 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. > Both lift and drag is a function of a square of the relative fluid velocity over the surface. So the faster you "slip" the paddle through the water, the more force you get out of it, you will not get any thrust without "slip". The slower the stroke the more "slip" you will get, the faster the less. But calling it "slip" implies it is an undesirable motion, which is the wrong idea. The thrust is intrinsic to the movement itself and a result of it, not related to efficiency at all. Because the perceived resistance is a function of the square of the relative fluid velocity, the same paddle pulled back rapidly through the water would have more resistance (less perceived "slip"), and pulled slowly would have less resistance (more perceived "slip"). So it is non-sensical to say the less slip you have in the water the more efficient the paddle design, they are not related. The only practical comparison of efficiency is comparing the total power required to push the same kayak, at the same speed, in the same conditions. The perceived resistance against a solid object is a direct function of the speed you push against it (not a square of the speed as in a fluid), and the slippage against the solid object would indicate a loss of perceived resistance (remember sliding friction is always lower than static friction). This is why the idea of slippage in a fluid, which comes from this model of pushing against a solid object, is invalid. Thrust as a result of fluid motion is not comparable to slippage. Unlike an airplane wing however, both components of lift and drag can be useful in a paddle stroke, and both can also cause wasted effort. the optimum shape for a paddle (and the optimum stroke style), that takes advantage of this would be anybody's guess, and likely only determined with lots of trial and error. Get the idea of "slippage" out of your vocabulary when considering fluid generated thrust. Power is a work rate, to define efficiency with anything other than "power in", or reduce it to something not related to power, is clearly invalid. You can not compare pushing against concrete to pushing against a fluid. Push very slowly against concrete, you get thrust, push fast, you get slippage. Push very slow against a fluid, you get nothing, push fast you get thrust exponential to the speed you push at. Resistance against a fluid is not related to efficiency. "Slippage" in a fluid is a nonsensical notion, and not a measure of efficiency. > > > > >> 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? My statement is correct, you have not thought this through. Just because you pull a paddle strait back does not mean your effort "will go directly to propelling the boat". You will push water in every direction (including backwards), but you also get turbulence. Turbulence heats the water and pushes it in directions not useful for forward movement, using up power and therefore it is wasted effort, i.e. poor efficiency. You want to accelerate the mass of the water exactly aft so you get forward thrust, accelerating the mass of the water in any other direction (as in turbulence) results in wasted effort. The cleanest way to accelerate the mass of water mostly aft is with the least amount of turbulence, this is done with a high aspect ratio surface with a foil shaped cross section. This is a FACT of fluid mechanics, if you do not understand this, nor simply can not accept it as a fact, than there is nothing else I can do for you. The fact that a propeller moves perpendicular to the line of travel to make forward thrust demonstrates your statement is false. If a general statement is false in one circumstance, than it is a false statement. the way a propeller gets thrust with motion at right angles to the direction of travel is because it pushes the water aft with the least amount of lost power, therefore it is more efficient than a paddle wheel, which is why paddle wheels are not used in commercial ships anymore. > > 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. Well is not efficiency what we are talking about? You can paddle a kayak by pulling a tennis racket strait back, you'll will make lots of turbulence, i.e. wasted effort, and it would not be efficient. Do not confuse the effort in pulling back the paddle with the motion of the water over the blade. since the kayak is moving forward, you have to pull back on the paddle to get any thrust out of it, the question is HOW you are getting that reaction at the handle by pushing on a fluid, and how to get that with the least amount of wasted effort. If you can increase the amount > of water you move without increasing the velocity at which you move > it, you will be more efficient. > False, it is unrelated. If this were true why not use giant paddle blades? You would increase the amount of water you push back at the same velocity, but YOU WILL NOT INCREASE EFFECENTCY. Efficiency is a measure of power consumption compared to useful work done. Power is a work RATE, i.e. it is time related, units are foot-pounds per minute, velocity is measured as feet per minute. They are not related, and for a kayak the only thing that is useful is to compare the amount of power it takes to move the same kayak, at the same speed, in the same conditions. Paddling fast or slow is not by itself a measure of power consumed. > 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. > If you do not realize how irrational this statement sounds to someone who works in fluid mechanics is, I can not clarify it for you. Mass and velocity, by themselves, ARE NOT RELATED to efficiency. Power input is, this is a work RATE. > 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. THIS IS LUDICRUS!!! Any fluid that is not moving aft, is wasted effort, F=Ma. If it is does not accelerate backwards, it is not useful for moving you forward. All of the power it takes to move the water in any direction beside strait back is wasted, and it comes only from your efforts, wasted effort. The only momentum that is going into your boat, is equal to the amount of momentum of the water going back! Vortexes, turbulence, lateral water movement is LOST POWER. > 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. Wrong, wrong, wrong, wrong. If you were a student in a senior level engineering class, I would send you back to freshman physics if you made a statement like this. I am not trying to belittle you, I just can not address something so totally out of step with the laws of physics without teaching you from scratch. And I am not about to do that here. > 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? Wrong, wrong, wrong!!!!! Your logic is faulty. I did a little calculation for you. But to make the comparison valid you have to use the same size wing in the glider as the area of the parachute, and both have to weigh the same. With these conditions, a well designed glider will sink at a rate of 45 feet per minute, an equivalent round parachute will sink at 1500 feet per minute!!!. You do not need to throw the glider, just drop it at the right angle of attack with the tail trimmed properly, it will convert the initial vertical velocity in to horizontal velocity. Do not question these calculations because I am not going to explain them, they are way too complicated to quickly make sense of them if you do not know how to do it. Go take a class and learn something about it and do the calculations for yourself and you will see these numbers are accrete. I used very typical specifications for a sail plane, and for a typical round parachute, that is what you get; the parachute smashes to the ground 33 times faster than the glider would touch down. you need a parachute 33 time bigger to get the same sink rate. The glider is way more efficient no matter how you measure it, either by sink rate, or by maximum distance traveled: in the same hundred feet drop the glider would have traveled 2300 horizontal feet, the best you could get from a round parachute is about 300 feet (of course the "para sail" type would be better, that is why round ones are not used anymore). You are not making valid comparisons, and your measure of efficiency is irrational. The speed the parachute sinks is not related to efficiency, it has nothing to do with a work RATE. > 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. > I thought we were talking about efficiency here? If you agree that the high aspect ratio paddle is more efficient, than that was what I was saying since the first post! Increasing the blade area is not related to efficiency. <snip> > You are confusing human efficiency with paddle efficiency. WHAT?!! Efficiency is related to the amount of power it takes to push the same kayak, the same speed. The only source of power is the human, NOT THE PADDLE. The paddle has no source of power other than the human. You are the one confused. When I say the high aspect ratio paddle is more effic ient, I am talking about the amount of human power it takes to move the kayak the same speed (using proper technique) is less than when using a low aspect ration paddle. Anything else is meaningless. Human efficiency is related to how much food a human eats compared to how much useful work the human does. What are YOU talking about? > 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). You can not make this assumption, most low aspect ration Euro blades have the totally wrong foil shape to generate good thrust. The typical shape on the low pressure side of a Euro blade spoils the flow over it and stalls the blade, the high aspect ratio blade is way more sensitive to stalling, virtually all native style paddles have foil shapes that are smooth on both surfaces, this improves flow and thrust, and reduces turbulence. You also must optimize the foil shape for each aspect ratio to take advantage of it, you can not keep the foil shape the same and have a valid comparison. But most Euro blades do not have a foil shape at all, the shape kills all the useful thrust that you could get off the low pressure side (and some shapes kill the thrust off the high pressure side too!). Realize that the idea of the "thrust" face of the paddle is also inaccurate, on a well shaped blade 75 percent (or more) of the thrust comes from the low pressure side, the face opposite the "thrust" face. This is a fact of fluid mechanics, do not argue with it. This is also why most (but not all) recreational Euro paddles are also inefficient, they have VERY poor low pressure surface shapes. This is another one of those areas that "common knowledge" and intuitive thinking about fluid mechanics leads to very wrong ideas. > However: > - Everything else being equal the paddle with the largest blade area > will be the most efficient. WRONG! size is not related to efficiency. > - Everything else being equal the lightest paddle will be the most efficient. True, but we are not comparing weight, we are comparing aspect ratio. > - Everything else being equal the fastest cadence will be the most efficient. This may be true, but has nothing to do with aspect ratio of the blade. > - Everything else being equal the boat with the strongest paddler > will be the fastest. But it does not mean he is more effect, just faster. > - Everything else being equal the paddler with the best technique > will be the fastest. And each size and shape of blade may take a different technique to get the best performance out of it, and fastest is not necessary more efficient. The one with the best technique, using the same paddle, will be more efficient (use less engird to go the same speed and distance). Be again I was comparing aspect ratio. <snip irrelevant statements> > > 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. This is not necessarily true. The optimum thickness of the foil is related to the Reynolds's number, a ratio of viscosity, size of the foil, and speed of the fluid. Thicker can be better under some conditions. > 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. Another advantage, which has nothing to do with efficiency, is because they are not feathered, and the blade is symmetrical on both sides, and there is no "front" and "back" or "up" and "down", you are less likely to mess up an emergency brace, or a roll, because you have the paddle held the wrong way. > > 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. I am not dogmatic about native paddles. I actually think there are areas that it can be improved, though you may risk diminishing the paddle's ability to do other functions beside moving the boat forward. Also I do not think I have seen anyone make a high aspect "native" style paddle with light weight composites, with a foam core. Traditionalists would probably cry foul, but it would be interesting to see what could be done with composites. I am not against innovations, and I have seen modern paddles that look excellent. It is just that most of the recreational sea kayak paddles I have seen commonly available have very poorly shaped blades. When I can make a better paddle in a few hours in my garage with a 2x4, I can not spending $200-$300 for something that performs so poorly. That is way more than I ever want to write about that. Forget about fluid mechanics and theory, just make or borrow a native style paddle, learn how to use it, and find out for your self. Peter Chopelas *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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At 3:29 AM -0700 5/18/01, Peter A. Chopelas wrote: > > > >> 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? > > >My statement is correct, you have not thought this through. Just because >you pull a paddle strait back does not mean your effort "will go directly >to propelling the boat". You will push water in every direction (including >backwards), but you also get turbulence. Turbulence heats the water and >pushes it in directions not useful for forward movement, using up power and >therefore it is wasted effort, i.e. poor efficiency. As Michael Edelman pointed out, my statement at the top amounts to a tautology. As he paraphrased it: "force that produces thrust, produces thrust." If you choose to argue "X" does not equal "X", I can only conclude that you are more interested in insulting me than in having a reasonable discussion. I'm sorry, I will not participate. I learn from your disagreement, but your insults are worthless to me. 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/ ***************************************************************************
Well, this is going to get very technical, although it only really requires high-school physics, so those of you who don't like that should delete this now. "Peter A. Chopelas" wrote: } Subject: RE: [Paddlewise] paddle sizing and Technology guides design > > Because the perceived resistance is a function of the square of the > relative fluid velocity, the same paddle pulled back rapidly through the > water would have more resistance (less perceived "slip"), and pulled slowly > would have less resistance (more perceived "slip"). So it is non-sensical > to say the less slip you have in the water the more efficient the paddle > design, they are not related. The only practical comparison of efficiency > is comparing the total power required to push the same kayak, at the same > speed, in the same conditions. Slippage and efficiency are related, and what is more, it can be mathematically related to power required. > The perceived resistance against a solid object is a direct function of the > speed you push against it (not a square of the speed as in a fluid), and > the slippage against the solid object would indicate a loss of perceived > resistance (remember sliding friction is always lower than static > friction). This is why the idea of slippage in a fluid, which comes from > this model of pushing against a solid object, is invalid. Thrust as a > result of fluid motion is not comparable to slippage. Wrong. > Get the idea of "slippage" out of your vocabulary when considering fluid > generated thrust. Power is a work rate, to define efficiency with anything > other than "power in", or reduce it to something not related to power, is > clearly invalid. Power = force*velocity, remember. So if you pull the paddle blade backwards faster than the kayak moves forward (slippage), you're using more power than is going into propelling the kayak. (The forces must be equal by Newton's third law.) That's a direct measure of efficiency. Yes, it's true that there is no way to have zero slippage - that's why it is impossible to have 100% paddle efficiency. It's still desirable to minimize the slippage. Where is the extra power going? Kinetic energy of the water. The power required to propel a kayak must counteract the drag, a force. To do that, we push/pull the water backwards, resulting in a momentum transfer from the water to the kayak, producing thrust to counteract the drag. The mathematical relation is force = dp/dt, momentum transfer rate. So for a given kayak velocity, we need to have a given momentum transfer rate. Now, let's look at the water. Momentum is mass*velocity, so for a given momentum transfer, we can move either a large mass of water slowly, or a small mass of water quickly. Which is better? Well, let's look at kinetic energy. Kinetic energy is 1/2 mv^2, proportional to the square of the velocity. So if we move a smaller mass of water more quickly, it will have more kinetic energy than if we moved a larger mass of water more slowly (but using the same momentum transfer). If we want maximum *energy* to go into propelling the kayak, and not into pushing the water backwards, we must move as large a mass of water as possible, as slowly as possible. And if we do this with the same amount of momentum transfer, we will have exactly the same thrust. BTW, this same problem comes up in aircraft propulsion - it's much more efficient to move larger quantities of air more slowly than small amounts of air very quickly. That is why modern fanjet engines are so large in diameter - most of the thrust is "bypass" thrust generated by the very large fans. > You want to accelerate the mass of the water exactly aft so you get forward > thrust, accelerating the mass of the water in any other direction (as in > turbulence) results in wasted effort. The cleanest way to accelerate the > mass of water mostly aft is with the least amount of turbulence, this is > done with a high aspect ratio surface with a foil shaped cross section. > This is a FACT of fluid mechanics, if you do not understand this, nor > simply can not accept it as a fact, than there is nothing else I can do for > you. This "FACT" is simply not true. And you need to give some support for your assertion beyond just saying it is a "FACT". > > 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? > > The fact that a propeller moves perpendicular to the line of travel to make > forward thrust demonstrates your statement is false. A propeller moves perpendicular to the line of travel, but applies a force parallel to the direction of travel. Nick's statement is true - he said force applied parallel, not motion parallel. > If you can increase the amount > > of water you move without increasing the velocity at which you move > > it, you will be more efficient. > > False, it is unrelated. If this were true why not use giant paddle blades? > You would increase the amount of water you push back at the same velocity, > but YOU WILL NOT INCREASE EFFECENTCY. Efficiency is a measure of power > consumption compared to useful work done. Power is a work RATE, i.e. it is > time related, units are foot-pounds per minute, velocity is measured as > feet per minute. They are not related, and for a kayak the only thing that > is useful is to compare the amount of power it takes to move the same > kayak, at the same speed, in the same conditions. Paddling fast or slow is > not by itself a measure of power consumed. Again, see above. It is entirely related; and giant paddle blades would be very efficient if you could use them practically. > > >> 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? > > My statement is correct, you have not thought this through. Just because > you pull a paddle strait back does not mean your effort "will go directly > to propelling the boat". You will push water in every direction (including > backwards), but you also get turbulence. Turbulence heats the water and > pushes it in directions not useful for forward movement, using up power and > therefore it is wasted effort, i.e. poor efficiency. He didn't say his "effort" will go into propelling the boat; he said the force applied. And this is true; Newton's Third Law is not repealed for fluid mechanics. But as discussed above, the *power* applied will not all go into propelling the boat; some of it will go into propelling the water. Again, be careful not to confuse momentum and energy here - you must have an equal amount of momentum propelling the water and the kayak by the Third Law, but you want maximum *power* (energy/time) going into boat propulsion, not water propulsion. Turbulence, etc. is all part of the kinetic energy of the water. All that factors into the amount of slippage. > You want to accelerate the mass of the water exactly aft so you get forward > thrust, accelerating the mass of the water in any other direction (as in > turbulence) results in wasted effort. The cleanest way to accelerate the > mass of water mostly aft is with the least amount of turbulence, this is > done with a high aspect ratio surface with a foil shaped cross section. > This is a FACT of fluid mechanics, if you do not understand this, nor > simply can not accept it as a fact, than there is nothing else I can do for > you. You're confusing airplane & glider wings (and propellers) with paddles. The FACT of fluid mechanics is that a high aspect ratio wing on an airplane gives you is a maximum lift/drag ratio. This is important for airplanes because the lift counteracts gravity to allow it to fly, while the drag must be counteracted with engine thrust. And propellers give maximum thrust for minimum rotational drag with a high aspect ratio. But it's very unclear to me that a high lift/drag ratio is important in a paddle - please demonstrate why. > > 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. > > THIS IS LUDICRUS!!! Any fluid that is not moving aft, is wasted effort, > F=Ma. If it is does not accelerate backwards, it is not useful for moving > you forward. All of the power it takes to move the water in any direction > beside strait back is wasted, and it comes only from your efforts, wasted > effort. The only momentum that is going into your boat, is equal to the > amount of momentum of the water going back! Vortexes, turbulence, lateral > water movement is LOST POWER. You're confusing momentum and energy. Nick is right; how the momentum dissipates itself is unimportant. What is important is how much power (energy rate) goes into moving the water vs. moving the boat. You need a given momentum transfer rate to counteract drag, and what you need to do for maximum efficiency is move the water as little as possible to create that momentum - which means moving as large a mass of water as possible. > Realize that the idea of the "thrust" face of the paddle is also > inaccurate, on a well shaped blade 75 percent (or more) of the thrust comes > from the low pressure side, the face opposite the "thrust" face. This is a > fact of fluid mechanics, do not argue with it. References for this "fact" of fluid mechanics? Where is there a technical discussion of *paddle* thrust that we can find this demonstrated for typical paddle usage? I think you're confusing paddles with propellers & wings again. I really love all these assertions followed by "do not argue". > > However: > > - Everything else being equal the paddle with the largest blade area > > will be the most efficient. > > WRONG! size is not related to efficiency. Yes it is, everything else being equal, because a larger paddle will move a larger amount of water, more slowly. The same momentum transfer will result in a higher proportion of energy being applied to the kayak (counteracting drag) and a lower proportion to the water. Again, this is because momentum is proportional to velocity, and kinetic energy to velocity squared, so for the mimimum water kinetic energy, you need mimimum velocity. Efficiency is all about converting the power applied into thrust, not kinetic energy of the water. Larger blades are more efficient. -------------------- That doesn't make them easier to use, however. Personally the paddle I most enjoy using is a Betsy Bay greenland-style paddle. I just like the feel of it, and I find it more fun to roll with. *************************************************************************** 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/ ***************************************************************************
Bob Myers wrote: > Slippage and efficiency are related, and what is more, it can be > mathematically related to power required. I do not know on what basis you say this, but with regards to my last posting I suppose this could be argued but it is not nearly enough information by itself to determine efficiency, and all of the other complicated relationships that would have to be included to the equations. By itself it is meaningless, see my last posting. > So if you pull the paddle blade > backwards faster than the kayak moves forward (slippage), you're using > more power than is going into propelling the kayak. (The forces must > be equal by Newton's third law.) That's a direct measure of > efficiency. I am sorry, this is not a measure of efficiency as I would define in my last post. Slippage, whether related or not to efficiency, would be included in the total efficacy if you just directly measured power in at the same speed. Beside, what makes you think a high aspect ratio paddle will have high slippage? If you make two paddles with exactly the same blade areas, one high aspect ratio, and low aspect ratio, the high aspect ratio paddle will consume less power moving you the same speed in the same kayak in the same conditions. There is no reason to assume a high aspect ratio paddle will slip more than a low aspect ratio paddle. It will not in fact. > we can move either a large mass of water > slowly, or a small mass of water quickly. Which is better? > Well, let's look at kinetic energy. Kinetic energy is 1/2 mv^2, > proportional to the square of the velocity. So if we move a smaller > mass of water more quickly, it will have more kinetic energy than > if we moved a larger mass of water more slowly (but using the same > momentum transfer). If we want maximum *energy* to go into propelling > the kayak, and not into pushing the water backwards, we must move > as large a mass of water as possible, as slowly as possible. And > if we do this with the same amount of momentum transfer, we will have > exactly the same thrust. Okay, so what? Again what makes you think a high aspect ration paddle (vs. a low aspect ratio paddle of the same area), will not move a larger mass of water slower? There is nothing in anything I posted that would lead you to this assumption. Your arguments are academic, if you simply compare power consumed going the same hull speed the high aspect ratio paddle will be lower. And your arguments are not true anyway, the most efficient aircraft wing (with the least amount of drag) is the SMALLEST one that generates enough lift to stay in the air. And given wings of the same size, the lowest drag will occur with the highest aspect ratio. There is a complex interaction between tip vortex, skin friction, form drag, induced drag, and a bunch of other stuff that affects both paddles and wings (and propellers too). > > BTW, this same problem comes up in aircraft propulsion - it's much > more efficient to move larger quantities of air more slowly than > small amounts of air very quickly. That is why modern fanjet engines > are so large in diameter - most of the thrust is "bypass" thrust > generated by the very large fans. Ahem, larger diameter fans have higher aspect ratio blades. They have to run slower to keep the tips subsonic, I know I have also done turbine design once in my career (they too have VERY complicated relationships with shape, speed, etc.). If there was a way to get the tip speed up without going sonic, we would do that, it would keep the weight down and improve the efficiency of the engine. Fortunately, paddles move at speeds way below sonic and cavitation speeds in water and this is not an issue. > And you need to give some > support for your assertion beyond just saying it is a "FACT". Well I am not going to teach you what you need to know here so you can know it is a fact, but the information is out there for you to find. I can not prove it to you unless you are willing learn what it take so you can know it too, and I do not have to time to teach you even if I wanted to. If you do not know, then the onus is on you to go and learn it. I want to tell you it was not just my education that taught me this, but also many mega hours of paid experience doing research, wind tunnel testing, and doing computational fluid mechanics (CFD). So have at if you want, but my assertion are not made by speculative suppositions. I also have hundreds of miles in canoes, much less in kayaks, but both with Euro paddles and only recently with native style blades. The high aspect ratio blade is more efficient. > A propeller moves perpendicular to the line of travel, but applies a force > parallel to the direction of travel. Nick's statement is true - he > said force applied parallel, not motion parallel. True enough. But the force applied, by itself, tells you nothing about efficiency. And much of the ENERGY you apply to the water does not go to propelling the boat forward. > > Again, see above. It is entirely related; and giant paddle blades would be > very efficient if you could use them practically. > Again I want to point out I am saying the high aspect ratio blade is more efficient, size is not part of my argument. But you forget something, you increase wetted area with bigger paddles, there is a point were you will lose efficiency, you can not look at only one feature of the design in isolation. Besides I would argue that the high aspect ratio blade will accelerate more water, with the least amount of lost power, than a low aspect ratio blade even if it is larger. Lager also gets heavier, and must be stiffer. > > And propellers give maximum thrust for minimum rotational drag with a > high aspect ratio. But it's very unclear to me that a high lift/drag > ratio is important in a paddle - please demonstrate why. For both airplane wings and propeller (and paddles), the component of drag that goes down with increasing AR is called induced drag. this is the drag it "costs" you to generate the thrust, the more thrust you generate off the foil surface (whether it be up to counter gravity as in a wing, or to get forward movement on a propeller or a paddle), the higher the induced drag. This drag on the paddle is not useful to help pull you through the water (the reason is very complicated). The fact is it just takes power to create the thrust off the moving fluid. You have to accelerate the fluid to get thrust off of it, that cost power, and it is a well known phenomenon that high aspect ratio surfaces require less power to generate the same amount of thrust. . You > need a given momentum transfer rate to counteract drag, and what you > need to do for maximum efficiency is move the water as little as > possible to create that momentum - which means moving as large a mass > of water as possible. And given the same amount of blade area, you can move more water, with less turbulence with less power, with a high AR paddle than with a low AR blade. > > > Realize that the idea of the "thrust" face of the paddle is also > > inaccurate, on a well shaped blade 75 percent (or more) of the thrust comes > > from the low pressure side, the face opposite the "thrust" face. This is a > > fact of fluid mechanics, do not argue with it. > > References for this "fact" of fluid mechanics? Where is there a > technical discussion of *paddle* thrust that we can find this > demonstrated for typical paddle usage? > Lots of them, look in any standard senior level fluid mechanics text books. If you do not know this I can not prove it to you, but you may beable to prove it to your self. Take a paddle with smooth surface on both sides and paddle a timed distance with your normal energy output rate for touring (if you could measure oxygen uptake you could verify your power output is the same, heart rate would also work as long as you are in a steady state out put mode). Then cover the low pressure side with something that will spoil the flow over it, say duct tape with a length thick rope under it running along the length of the blade near the edges. Do the run at the same energy out put. Repeat it with the spoiler on the "thrust" face. Compare each with the base line. You must use a paddle with a smooth low pressure face. Most commercial paddles have very poor low pressure faces, they attach the handle on the "back" (side opposite from the "thrust" face) and make no attempt to smooth the attachment. These already have spoiled flow over the low pressure side and the test would not be valid. Also you may want to experiment with the stoke mechanics a bit to get a stoke that feels good before you do the test "run". Also do not attempt to "race", under extreme loading the flow on the surfaces behaves differently, you want to test this at normal "touring" conditions. Do this and you will know for yourself. You could just try it without the timing, you can feel the difference. If the object was just to move water backward why not use a tennis racket, all that turbulence would absorb a lot of energy, but not a lot of it would go into forward motion of the kayak. > I think you're confusing paddles with propellers & wings again. > Nope, not at all. ANY surface, that produces thrust in ANY fluid works the same way: wings, pumps, propellers, turbines, insect wings, bird wings, paddles, swim fins, fans, etc. etc. You are the one that do not understand that I am not confusing anything, because you do not understand the principle. It is not intuitive at all, and from my experience when I started my career, not that easy to grasp either. > I really love all these assertions followed by "do not argue". > If you have the same experience that I do, you would not be arguing. And until you do you are in no position to argue against it. I can not give you that experience, but I commend you go to figure out what I am writing rather than argue from inexperience and ignorance. That is why I say do not argue, but you argue any way. Go do the test I gave you and prove it for your self. One of my engineering professors told me that one simple test is worth 1000 expert opinions. But instead you want to argue. In every post I suggested everyone just go out and try it, (and not to argue). But instead you do not try it, you just argue. Do not take my word for it, go prove it for your self. > Larger blades are more efficient. > A totally unqualified statement, and certainly not one based on taking measurements. > Personally the paddle > I most enjoy using is a Betsy Bay Greenland-style paddle. I just like > the feel of it, and I find it more fun to roll with. Did you ever stop and consider why if "feels" better? Why it is easier to roll with? Perhaps it responds better to your energy input, has better control because it creates less turbulence and generally coverts your power more efficiently in to thrust for both forward movement, and steering and control inputs (and rolls). Just maybe? Peter *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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From: "Peter A. Chopelas" <pac_at_premier1.net> > There is no reason to assume a high aspect ratio paddle will slip more than > a low aspect ratio paddle. It will not in fact. > In "The Shape of the Canoe", John Winters writes: "... my tests show that the lower aspect ratio paddles are somewhat more efficient (Fig 50 - he shows a graph with thrust decrease vs aspect ratio). This appears to fly in the face of aeronautical research [...] A possible explanation is that wave making resistance is higher for wide shallow paddles. " He goes on to say that the paddle is used at the interface of two fluids of different properties and that there is an impulse effect and not just a steady-state flow, both of which can affect the results relative to the aerodynamic theory. Experiment beats theory any day, especially if the experiment doesn't leave out what the theory does. > I also have hundreds of miles in canoes, much less in kayaks, but both with > Euro paddles and only recently with native style blades. The high aspect > ratio blade is more efficient. Your experimental background should make you less inclined to go with a subjective conclusion. Have you actually _measured_ this efficiency or have you just decided the paddle makes you feel better? > Larger also gets heavier, and must be stiffer. And longer doesn't? Don't forget you are comparing a thick wood paddle to a thin composite paddle. Most woods have stiffness-to-weight ratios that can't be beat by other materials without going to extremes. Unless you go to foam-cored graphite/boron/whatever (to get the volume up), wood almost always wins. > For both airplane wings and propeller (and paddles), the component of drag > that goes down with increasing AR is called induced drag. Given that the chord length of a paddle is next to zero, wouldn't that imply that induced drag is negligible? Assuming here a composite blade. Or to put it another way, the drag on the blade as a flat plate swamps the induced drag. Besides, why would you want _less_ drag? Drag is what makes the paddle work! > You must use a paddle with a smooth low pressure face. Most commercial > paddles have very poor low pressure faces, they attach the handle on the > "back" (side opposite from the "thrust" face) and make no attempt to smooth > the attachment. These already have spoiled flow over the low pressure side > and the test would not be valid. > My expectation is separation of the flow at the edge of the paddle with eddies coming off both sides, possibly with Karman vortex trails causing flutter. How does a wide, flat(ish) blade result in a flow on the back face? Mike *************************************************************************** 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: RE: [Paddlewise] paddle sizing and Technology guides design > Bob Myers wrote: > > Slippage and efficiency are related, and what is more, it can be > > mathematically related to power required. > > I do not know on what basis you say this, but with regards to my last > posting I suppose this could be argued but it is not nearly enough > information by itself to determine efficiency, and all of the other > complicated relationships that would have to be included to the equations. > By itself it is meaningless, see my last posting. See *my* last posting. I understand efficiency the same way you do - power output / power input. Your somewhat condescending previous posting tried to imply that we do not understand you or the concept of efficiency, but that is not so. > There is no reason to assume a high aspect ratio paddle will slip more than > a low aspect ratio paddle. It will not in fact. I've actually made no assertion about whether a high aspect ratio paddle is more or less efficient. Others have, including John Winters; I would suggest you bring that up with him. I believe that John has claimed to have done some controlled experiments concerning this, something I don't believe you haved claimed as yet. What I've been primarily pointing out is that slippage is directly related to efficiency, which is something you have been denying. > And your arguments are not true anyway, the most efficient aircraft wing > (with the least amount of drag) is the SMALLEST one that generates enough > lift to stay in the air. And given wings of the same size, the lowest drag > will occur with the highest aspect ratio. There is a complex interaction > between tip vortex, skin friction, form drag, induced drag, and a bunch of > other stuff that affects both paddles and wings (and propellers too). Again, what exactly does an efficient aircraft wing have to do with a paddle? You have not shown any direct relationship between the efficiencies of an aircraft wing and a paddle. Just saying that it's all fluid mechanics doesn't cut it. Paddle drag that is parallel to the direction of motion is actually useful for thrust - airplane wing drag (and propeller drag) is not. > True enough. But the force applied, by itself, tells you nothing about > efficiency. And much of the ENERGY you apply to the water does not go to > propelling the boat forward. Right, that's what slippage tells you - how much of that energy is not propelling the boat - the efficiency of your power usage. > If the object was just to move water backward why not use a tennis racket, > all that turbulence would absorb a lot of energy, but not a lot of it would > go into forward motion of the kayak. Because it would have horrible slippage rates, as I've discussed. You could move the tennis racket backwards very quickly, but all you'd be doing is moving very small amounts of water very quickly - that is very inefficient because too much of your power goes into moving water instead of counteracting boat drag - yes, moving it turbulently, but primary point is moving at high velocity. The object, as I've said all along, is to move as large a mass of water, as slowly as possible, as directly aft as possible. Your tennis racket comment seems to show that you have not been paying any attention to my argument. > > I think you're confusing paddles with propellers & wings again. > > > Nope, not at all. ANY surface, that produces thrust in ANY fluid works the > same way: wings, pumps, propellers, turbines, insect wings, bird wings, > paddles, swim fins, fans, etc. etc. Assuming similar angles of attack, yes. Most of those surfaces operate at fairly low angles of attack, less than 15 degrees or so. But what is the angle of attack of a kayak paddle? Pretty high, especially if you use a low blade angle as is usually recommended for Greenland-style paddling. How much separation and turbulence are you going to get on the back side, no matter what its shape? As you go to very high angles of attack, is it not true that the upper surface of a wing loses effectiveness faster than the lower surface? *************************************************************************** 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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