I'm not sure but, I think the comparison of "rockets" and "paddles" may be apples to oranges, as they say. A rocket engine does not push against anything except the rocket body and that is why it can operate with, or without an atmosphere, or, even in water. A paddle must have something to push against (more like a jet engine than a rocket), to be effective. I know this is a small point but it's raining here in MN today and I can't go paddling. Ron *************************************************************************** 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/ ***************************************************************************
There seems to be some misunderstanding here about the physics of how things move. Hopefully I can explain some of this without boring or insulting anyone. Rockets and jets and cars and people's feet all push (exert force) on _something_. In the case of rockets and jets the something is the gases that are ejected to the rear. Extremely high pressures are created inside the rocke/jet engine and gases can only escape from the rear so there is resulting force towards the front that drives the vehicle. A kids balloon is a rocket vehicle. Air inside is under pressure, when the neck is closed the pressure/force in all directions is the same and the balloon sits there. When it's untied, air can escape and there is a net force in the direction opposite that of the escaping gases. Same in Jets. In jets and rockets tremendous pressures are generated by heating gases. In jets some of the gas is sucked in the front. In rockets all of the gases are the result of burning something. If the exit is blocked and pressure gets higher than the strength of the walls of the combustion chamber, they explode. When operating properly, the resultant force is proportional to both the velocity imparted to the material exhausted and mass of the material exhausted. The water in a jet ski exhaust doesn't have to move as fast to create an identical force as the gases in the exhause of a rocket motor have to move, because the water is denser than the gas. Propeller planes work because the propeller accelerates air towards the rear of the plane, boat propellers the same, acellerating water. Tires and feet accelerate the world and result in drive of the vehicle/ person in the other direction. In the last two cases if the friction is low (ice?) the force exerted on the world is low and the forward drive is low. The mass of the world is so large that the effect of the forces of tires and feet is generally negligible. The fact that tires and feet are generally exerting forces in different random directions tends to cancel out these relatively negligible forces, also. With kayaks, forward force is equal to the product of the acceration of the water times the mass of the water moved. If there is a lot of slippage (small area paddle blade = small mass of water) the paddle has to move backwards faster to get the same forward force, as you get with a large area blade (large mass of water) and slower movement of the water/ blade. If you move the same paddle slowly, you get less resultant force than if you move the paddle faster, as the force generated is proportional to speed achieved (acceleration). If you move a teeny paddle blade and a huge paddle blade at the same speed in the water you get more force to move the kayak from the huge blade. The force comes, originally from your body, so moving the small blade, at a given speed, requires less energy from you than large blade, moved at the same speed. Another example of the same principles of physics is a person throwing a baseball and a shot put. The strength of the person is constant, the baseball goes faster than the shotput because it is lighter (less mass). If identical energy is expended to throw them, they will each contain the same energy and injure you the same, if they hit you. A Honda del Sol going 75 mph and weighing 1 Ton (75 ton/mph), will do the same damage as a loaded 18 wheeler going 5 mph and weighing 15 Tons (75 ton/mph). Hope I helped somebody, and didn't confuse too many, Fairwinds and happy bytes, -- ------------------------------------------------------------------------- Dave Flory, San Jose, CA. daflory_at_pacbell.net Go Sea Kayaking!! ------------------------------------------------------------------------- Speak softly and study Aikido, then you won't need a big stick. ------------------------------------------------------------------------- *************************************************************************** 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/ ***************************************************************************
Ron Dunnington writes: "A rocket engine does not push against anything except the rocket body and that is why it can operate with, or without an atmosphere, or, even in water. A paddle must have something to push against (more like a jet engine than a rocket), to be effective. " That's sort of my point. Rocket engines work on Newtonian principles -- very light particles of rocket exhaust accelerated to extreme speeds generates Newtonian thrust without anything to push "against." Paddles work more like wheels -- the paddle pushes against the friction of the water to move the kayak forward, relying much less on Newtonian reactive forces. Of course, all this intergalactic thinking has made me realize the error of my earlier post. The entire universe is Newtonian. When I accelerate my car, I must be imparting a certain (very small) acceleration to the spin of the earth as an equal and opposite reaction to the force of acceleration for my car. Of course, it doesnt matter much to me whether I get where I am going by moving my car to my destination, or spinning my destination closer to my car! I guess this proves Nick's point that moving a large mass a little bit is more efficient (in Newtonian terms) than moving a small mass very fast. But when paddling, moving water backwards is wasted energy. It is inevitable, but the less energy absorbed by the movement of water, the more energy is put to moving the kayak forward. So slippage, while inevitable, cant be a good thing . . . --Karl Coplan *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
At 01:35 p.m. 25/07/02 -0400, Coplan, Karl wrote: >Ron Dunnington writes: > >"A rocket engine does not push against anything >except the rocket body and that is why it can operate with, or without an >atmosphere, or, even in water. A paddle must have something to push against >(more like a jet engine than a rocket), to be effective. " > >That's sort of my point. Rocket engines work on Newtonian principles -- >very light particles of rocket exhaust accelerated to extreme speeds >generates Newtonian thrust without anything to push "against." I agree. Let me phrase it in more Newtonian Terms. The rocket does not need any atmosphere to push against. The Newtonian momentum conservation principle states that if there are no external forces, then the rocket should maintain its momentum. Internal combustion is not an external force. So if particles move back very quickly due to combustion, the rocket must move forward a bit so that the center of mass of the system particles-rocket maintains its momentum. If large amounts of combustion particles come out fast, the rocket gains speed in the opposite direction but the center of mass stays as it was. On the other hand paddling is like sticking a pole in the mud and pulling ourselves from it. There is an external force, or reference that the system uses to pull itself from. For an ideally perfect paddle , it would enter the water and stay right there. Then all the power would be transferred to move the kayak forward, against that fixed pole. Paddles are not ideal and if they were would be too difficult to use when starting to accelerate. Since paddles leak some water and suffer some displacement from the entrance point, some energy is lost, but also may help the paddler if he doesnīt want to put all his strength or if he wants to save some energy in long tours. Stronger paddlers will want better grip in the water. Weaker fast stroking paddlers will want some leaking to allow them to give more strokes with less force, even at the expense of some energy loss. Best Regards, Rafael el cayuco chief *************************************************************************** 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/ ***************************************************************************
Karl wrote: <SNIP>>>>>But when paddling, moving water backwards is wasted energy. It is inevitable, but the less energy absorbed by the movement of water, the more energy is put to moving the kayak forward.<<<<<SNIP> Moving water backwards results in your moving forward on its surface (in an equal and opposite way). Moving water to the side or in any other direction with the paddle (turbulence for one) expends energy that is being wasted, or is even working against you, to a greater or lesser degree (depending on its degree of backward component). Some loss is always inevitable to a greater or lesser degree-the percent of efficiency of any propulsion system will always be less than 1. However, the loss isn't in the water that is being moved straight backward, as you stated. <SNIP>>>>>>>The entire universe is Newtonian. <<<<SNIP> Actually, the universe is Brozinian (as will be widely recognized once I unify gravity with the other--already unified--forces). In the Brozinian universe the space-time continuum may be collapsing at an accelerating rate (the negative or "anti-" gravity). In this milieu of a collapsing ether, mass all appears to be accelerating outward away from itself . This apparent expansion (relative to the collapsing ether) creates the sensations of gravity to an observer inside the system. To a human observer it also appears as if all mass is racing away from each other as the result of a big bang that appears to have been centered at the point where the Brozinian universe is collapsing into. However, until some perception like the above becomes the general perception among physicists, the entire universe will still be considered to be Einsteinian rather than Newtonian. Granted, Newton came up with some very workable approximations for use at kayak speeds but you are nearly a century out of date. >From the center of MY universe, 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/ ***************************************************************************
From: "Matt Broze" <mkayaks_at_oz.net> > Actually, the universe is Brozinian (as will be widely recognized once I > unify gravity with the other--already unified--forces). In the Brozinian > universe the space-time continuum may be collapsing at an accelerating rate > (the negative or "anti-" gravity). In this milieu of a collapsing ether, > mass all appears to be accelerating outward away from itself . This apparent > expansion (relative to the collapsing ether) creates the sensations of > gravity to an observer inside the system. To a human observer it also > appears as if all mass is racing away from each other as the result of a big > bang that appears to have been centered at the point where the Brozinian > universe is collapsing into. You'll have to square this with Star Trek's concept of sub-space before I'll buy in. (physics - when will it all end????) 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/ ***************************************************************************
Ron Dunnington writes: > >"A rocket engine does not push against anything >except the rocket body and that is why it can operate with, or without an >atmosphere, or, even in water. A paddle must have something to push against >(more like a jet engine than a rocket), to be effective. " No, a jet is propelled in the same Newtonian manner as a rocket and does not need air to push against to work (rather it needs the air to supply the oxygen for combustion-a rocket carries its oxygen with it to do the same thing-i.e. push against the front of the inside of the combustion chamber where there is no equal push against the opposite side to nullify it (as is the case with the explosive expansion due to combustion pushing in all other directions inside the combustion chamber) because the combustion chamber is open on the back end where the expanding combustion gasses are free to escape. Raphael wrote: <SNIP>>>>>>If large amounts of combustion particles come out fast, the rocket gains speed in the opposite direction but the center of mass stays as it was.<<<<<<<<< No Way! The fuel in the rocket is a huge store of potential energy that when released will propel the rocket far beyond it keeping the same center of mass for it and its exhaust particles. This potential energy constitutes an outside force. The laws of motion you are talking about concern collisions between moving objects when no force beyond their existing masses and momentums is present or introduced. >>>>>> On the other hand paddling is like sticking a pole in the mud and pulling ourselves from it. There is an external force, or reference that the system uses to pull itself from.<<<<<<SNIP> Equal and opposite, just the same as with a rocket. You pull the mass of the world just a little bit towards you and just to keep things equal the much smaller mass of you and the kayak moves in the opposite direction, but a whole lot further than the earth did (to conserve energy and mass). >>>>>>> Paddles are not ideal and if they were would be too difficult to use when starting to accelerate. Since paddles leak some water and suffer some displacement from the entrance point, some energy is lost, but also may help the paddler if he doesn't want to put all his strength or if he wants to save some energy in long tours. Stronger paddlers will want better grip in the water. Weaker fast stroking paddlers will want some leaking to allow them to give more strokes with less force, even at the expense of some energy loss.<<<<<<<<<< I disagree. When starting to accelerate with the (impossible) "ideal" 100% efficient paddle you would just not pull as hard at first (or use a shorter length shaft). Energy is always lost (for doing useful work) to randomization (entropy) not necessarily by the blades displacement from the entry point straight back (although water moving in direction other than straight back (leakage?) will contribute to the displacement of the blade). The "ideal" paddle would still pull something back (even if it was the earth) in order to move the kayak forward. There would just be no loss in the system due to entropy (impossible). The differences between the paddle preferences of stronger and weaker paddlers will have much to do with the amount of muscle and joint strain they are willing to endure and the efficiency of their own bodies at different stroke rates. The length of the paddle (leverage) is most likely the best way to control the strain to muscle and joint (rather than purposefully making the blade less efficient). As pointed out earlier the higher stroke rate will be more efficient because it minimizes the losses due to greater acceleration during and deceleration between strokes with a slower stroke rate. Our coordination also puts limits on how fast we can efficiently stroke. I suspect that not only is Greg Barton especially strong and in excellent physical condition, but he is most likely extraordinarily quick of reflex and inordinately coordinated in order to place his paddle in the water in such a way that he doesn't get ventilation behind his blades during the powerful strokes (where most of us would be digging divots out of the water if generating that kind of power) while at the same time doing his imitation of a hummingbird. 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/ ***************************************************************************
Thanks to all for the bow rudder tips - this has been an elusive one for me to get right (I always feel like I'm about to fall out of the boat) and now have more things to try. And I certainly appreciate the Brozian Universe theories, but I am disturbed with the concept of moving water backwards as desirable. Please be kind to a very non-technical discussion. Having learned to row and swim before encountering a paddle, I learned the concept of 'anchoring' your blade (oar, hand, whatever) and pulling your vessel (boat, body, etc) past it. Of course, it's not a perfect world and your blade does move some backward - and I am assuming here we have minimized all the wasted sideways effort. The goal is to minimize the amount of water you move and maximize the amount of vessel you move. The vessel offers less resistance to the force (vertical brace?) than the water does, so you move forward more than your blade moves back. To optimize this ratio we lengthen the vessel and/or increase the ability of the blade to stay put in the water. I've only used a wing paddle a couple of times, but this is what I think that design does. Placed it in the water correctly, it holds fast and allows you to put serious force into moving the vessel. Of course, there's lots of reasons why we don't all use a wing paddle or hatchet blade all the time that don't have to do with efficiency of forward acceleration. But when I most desperately need to catch someone or some thing, I visualize each blade as immovable in the water for the duration of each stroke. If I've missed the point please let me know - there's still a few 'things' I can't catch! Yahoo! Health - Feel better, live better http://health.yahoo.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/ ***************************************************************************
Jennifer wrote: Of course, there's lots of reasons why we don't all use a wing paddle or hatchet blade all the time that don't have to do with efficiency of forward acceleration. But when I most desperately need to catch someone or some thing, I visualize each blade as immovable in the water for the duration of each stroke. If I've missed the point please let me know - there's still a few 'things' I can't catch! ------------------------------------------- The way I understand it and my personal point of view is that the shape of wing paddles are very effective in not dragging backwards. They donīt displace water sideways as much as other paddles and therefore water holds them tight in place and more power goes to move the boat forward. We have manufactured several types of paddles for our own use only. The first ones were kind of rounded on the back side, and you felt little effort to paddle. We use them for children now. But you also gain little speed. The paddle really displaces backwards and that is a loss of energy. When we want to accelerate fast we just see our paddles passing by us very quickly and little speed gained. We then made some flat section paddles with the same cross section as the previous ones. Now you could feel the force on your arms and torso if you want to give the same speed to your stroke. The blades offer more resistance to travel through the water and therefore give you better grip. It can be easily seen with braces. If you make a high brace with a rounded paddle you have to hip flick faster because you sink quicker. With the flat blade you can hold longer before a hip flick because the paddle does not sink so easily. Now if you place it sideways on the edge it will sink immediately. Our next paddle was flat with a little edge turned into the power side. That little edge was enough to retain more water and it was still harder to paddle because it had better grip still. It held water better, and we could accelerate faster. It had other inconveniences when bracing, sculling and other things. So we ended up with a design that is pretty flat, non symmetrical to avoid fluttering, with a little edge and pretty strong so that we can rest on it to get in and out of the kayak. So our conclusion is that the more means you use to stop water from sliding to the sides, the better grip you have, some ways to do it are larger area, wing shape, computerized shape, spoon shape, edges, etc. That does not mean that it will make one specific paddler more efficient since as many have said in this forum, many other aspects must be brought into consideration, including things like type of blade for type of boat. Best Regards, Rafael Mier-Maza el cayuco chief. *************************************************************************** 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 Matt, At 12:56 a.m. 26/07/02 -0700, Matt Broze wrote: >No Way! The fuel in the rocket is a huge store of potential energy that when >released will propel the rocket far beyond it keeping the same center of >mass for it and its exhaust particles. This potential energy constitutes an >outside force. The laws of motion you are talking about concern collisions >between moving objects when no force beyond their existing masses and >momentums is present or introduced. Sorry to disagree with you. Fortunately enough my disagreement is more in the academic part of basic physics than in the part related to the paddle efficiency. The rocket principle and why it moves when in vacuum is a classical problem of first college gear in the mechanics class. I agree that there is a lot of potential energy inside the rocket. I agree that explosion liberates a lot of energy. But you can not refuse the universal law that in close systems unperturbed by external (by external I mean external) forces must maintain their state of momentum. In outer space vacuum there is no mass (almost), no friction and no drag. But the paradox is that rockets change their state of speed. How can that happen without violating the universal law of momentum conservation? It is only because m1v1 of particles or gasses (mass) going out in one direction equal m2v2 of rocket in the other. To be more precise, the change in momentum in one direction equals the change in momentum in the opposite direction, so that resultant momentum stays the same. Once it moves, the next particle expulsion occurs with a different state of momentum because the rocket has already some speed, and then some more speed is gained and so on. If you want I can make a deeper or more detailed comment off line. On the other hand the system kayak-paddler-paddle move with respect to the media (called water) by interacting with it. Therefore that is an external force. The system must get in touch with the external environment to gain any speed. Everything else in my discussion follows from these statements. Best Regards, Rafael Mier-Maza el cayuco chief *************************************************************************** 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/ ***************************************************************************
(Moderator's Note: Content unaltered. Excessive quoting (i.e. headers/footers/sig lines/comments from previous posts, etc.) have been removed. Please edit quoted material and list footers when replying to posts.) One minor correction, if I may. There is mass of objects in space. I presume you mean "weight", which is determined by relative distance to another object. If not, you should study the fun problems of manipulating large objects in a zero G environment. It's easy to be crushed by a mass with momentum that has no "weight". Ex-NASA-ite, Dave G. Poquoson, Va. *************************************************************************** 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/ ***************************************************************************
(Moderator's Note: Content unaltered. Excessive quoting (i.e. headers/footers/sig lines/comments from previous posts, etc.) have been removed. Please edit quoted material and list footers when replying to posts.) Funny! Check out Bill Nye's video "momentum".....he uses rockets and I think he says much the same thing. I happen to know Rafael has a degree in physic - although Matt is a great science guy too. (I've got to admit I am jumping into catching up on email in reverse chronological order at midnight. I think there are over 1,800 messages in this box. And yes, I think everyone should dress for the water - or for varying conditions. In just leading trips across Port Townsend Bay I've seen too much evidence....) The latest scenario published in Sea Kayaker Magazine is more wonderful evidence of what can go wrong in a few short minutes. Maybe if those people had been dressed for the water they might have made it. Well written too. Andree Kayak Instruction Excellence http://www.onwatersports.com Port Townsend, WA *************************************************************************** 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/ ***************************************************************************
Hmm, this didn't seem to post last night.... On Sun, 28 Jul 2002, A. Hurley wrote: > Funny! > > Check out Bill Nye's video "momentum".....he uses rockets and I think he > says much the same thing. > > I happen to know Rafael has a degree in physics - although Matt is a great > science guy too. > > (I've got to admit I am jumping into catching up on email in reverse > chronological order at midnight. I think there are over 1,800 messages in > this box. And yes, I think everyone should dress for the water - or for > varying conditions. In just leading trips across Port Townsend Bay I've > seen too much evidence....) > > The latest scenario published in Sea Kayaker Magazine is more wonderful > evidence of what can go wrong in a few short minutes. Maybe if those > people had been dressed for the water they might have made it. Well > written too. > > Andree > > Kayak Instruction Excellence > http://www.onwatersports.com > Port Townsend, WA > > On Fri, 26 Jul 2002, > Rafael Mier Maza wrote: > > > Hi Matt, > > > > At 12:56 a.m. 26/07/02 -0700, Matt Broze wrote: > > >No Way! The fuel in the rocket is a huge store of potential energy that when http://www.viewit.com/ http://www.onwatersports.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/ ***************************************************************************
> >Check out Bill Nye's video "momentum".....he uses rockets and I think he >says much the same thing. > >I happen to know Rafael has a degree in physic - although Matt is a great >science guy too. This may sound funny, but I invite you to do the experiment I have done many times, since I am underwater often. I have experienced the rocket effect every time I use my bilge pump in tranquil waters. As I pump water, and water is leaving to the right of my kayak, the whole kayak moves slowly to the left, even though my arms are moving in a vertical direction pumping up and down. Same thing if water leaves left the kayak moves right. Thatīs a clear proof of momentum conservation. Try it. Another useful one has to do with the fact that when you start your roll with your hip flick, with your body far out from the kayak, and you bring the body into the kayak on a C to C roll or laying on the back deck, the rotation speed is increased, in order to conserve momentum. This is the same as an ice skater that is rotating and closes the arms. Momentum conservation increases his speed. If he opens the arms he slows down again. Best Regards, Rafael el cayuco chief *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
At 8:17 PM -0500 7/25/02, Rafael Mier Maza wrote: >At 01:35 p.m. 25/07/02 -0400, Coplan, Karl wrote: >>Ron Dunnington writes: >> >>"A rocket engine does not push against anything >>except the rocket body and that is why it can operate with, or without an >>atmosphere, or, even in water. A paddle must have something to push against >>(more like a jet engine than a rocket), to be effective. " >> >>That's sort of my point. Rocket engines work on Newtonian principles -- >>very light particles of rocket exhaust accelerated to extreme speeds >>generates Newtonian thrust without anything to push "against." > >I agree. Let me phrase it in more Newtonian Terms. The rocket does >not need any atmosphere to push against. The Newtonian momentum >conservation principle states that if there are no external forces, >then the rocket should maintain its momentum. Internal combustion is >not an external force. So if particles move back very quickly due to >combustion, the rocket must move forward a bit so that the center of >mass of the system particles-rocket maintains its momentum. If large >amounts of combustion particles come out fast, the rocket gains >speed in the opposite direction but the center of mass stays as it >was. > The mistake is to think that just because you are on the earth you have something to push against. The earth is floating through space just like the rocket. The rocket pushes a small mass out behind it to make it move. A person on the earth just has a much larger mass to push out behind. The physics is the same. The real difference is in perception. On a rocket the frame of reference is usually the rocket and not the mass you are pushing out behind. This makes it look like the mass of propellant does most of the moving. On the earth the frame of reference is usually the earth so it looks like the person does all moving. For the purposes of analysis you can usually ignore the motion of the earth even though the principles remain the same. However when you are on the water you are not all that strongly bound to the structure of the earth. When you try to push off of it by dipping your paddle in the water, you are dipping into a fluid that can move independently from the earth. As a result you need to treat paddling more like a rocket when you analyze it. -- 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/ ***************************************************************************
On Thursday, July 25, 2002, at 9:09:25 AM PST, Ron Dunnington wrote: > ...but it's raining here in MN today and I can't go paddling. Hello Ron, I've been reading these "paddle" threads with interest, especially since I've recently switched from using a "Euro" paddle to a W. Greenland style paddle. I have many developing thoughts on the different "efficiencies" of the different styles of paddles/techniques, but for the moment, I'll just comment on what you said about rain, quoted above. Why not paddle in the rain? When I go paddling (nearly every day, year 'round), I almost always practice a few rolls and/or I'm in the surf or crashing wind waves, so I'm often a bit wet anyway. A little fresh water from above doesn't bother me at all. In fact, because most people seem to equate rain with "bad" weather (I generally don't use the term "bad" when considering weather, as each kind of weather is lovely in its own way), you're more likely to have your favorite paddling spots all to yourself if you don't mind a little rain. With my dry top or dry suit, and the rain hat I sometimes wear, even if it's pouring rain, only my face and hands feel any water anyway. I like to paddle in just about any weather (hail, while exciting, can be a bit painful if one is not wearing a helmet...and horizontal hail will get your face anyway!), and rain, mist, fog, wind, etc. each invoke their own flavor of paddling bliss. If you can handle varying conditions, I encourage you to go out and enjoy paddling regardless of a little weather! Same thing goes for swimming in the rain...you're as wet as you'll ever get by just swimming, so what's the problem with swimming in the rain? (there must be a song and dance in there somewhere!). I also hope that you take advantage of paddling in snowy conditions. There's nothing quite so lovely as paddling around in that special quiet and beauty that only snow can provide. Just dress for the conditions and enjoy! :-) Melissa -- PGP public keys: mailto:pgp_keys_at_gmx.co.uk?subject=0x46C29887&Body=Please%20send%20keys *************************************************************************** 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/ ***************************************************************************
--- Melissa Reese <melissa_at_bonnyweeboaty.net> wrote: Snip... > Why not paddle in the rain? .... > I like to paddle in just about any weather .... > I also hope that you take advantage of paddling in > snowy conditions. I'm with you, Melissa. The only thing is here in summer 'rain' tends to mean a thunderstorm. Lightning and wind >30 knots are about the only constraints to a good paddle, though! Oh yeah, and frozen water. Yahoo! Health - Feel better, live better http://health.yahoo.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/ ***************************************************************************
At 12:56 a.m. 26/07/02 -0700, Matt Broze wrote: >No Way! The fuel in the rocket is a huge store of potential energy that when >released will propel the rocket far beyond it keeping the same center of >mass for it and its exhaust particles. This potential energy constitutes an >outside force. The laws of motion you are talking about concern collisions >between moving objects when no force beyond their existing masses and >momentums is present or introduced. That dummy Matt sure got this wrong! As hard as it is for me to "get off the rocket" and believe that the center of mass remains the same it looks like Raphael is correct here. I'm sorry I went off half-cocked, but even though I know now it must be true it is still hard for me to imagine that enough gases would be shot far enough out the back of the rocket to keep the center of mass of the whole system the same. When I was thinking about a rocket lifting off the earth against gravity I also neglected to consider that the earth was moved back with as much momentum as the rocket was moved forward. Things seem more clear in empty space. The lightweight exhaust gas particles will be traveling backward much further than the heavier rocket moves forward and the center of mass will stay in the same position. Thanks for making me think about this some more Raphael. I still think Raphael is missing his own well taken point when he wrote: <SNIP>>>>>>On the other hand the system kayak-paddler-paddle move with respect to the media (called water) by interacting with it. Therefore that is an external force. The system must get in touch with the external environment to gain any speed.<<<<<<snip> First off, even with this limited system size "kayak-paddler-paddle" (one that doesn't even include water yet) you would not need to get in touch with an external environment to gain some speed. You could simply throw the paddle to gain some speed in the opposite direction (without having to have the paddle interacting with water). But, why limit the size of the system to "kayak-paddler-paddle"? If you make the system: "kayak-paddler-paddle-water-earth" (and this could go on out to -galaxy-universe, but don't need to for this example) and you are not adding any new external force (one that isn't already operating consistently inside the system anyhow). Every action still will have an equal and opposite reaction. If you move the water (or earth) one way you will also move the kayak the opposite way and the center of mass will be conserved just like with the rocket ship. Something has to move one way for you to go the other. In a paddlers case it is some water. The faster and further you move the water one way the faster and further you will go the other. Nick wrote (in regards to my saying a faster stroke rate was more efficient because it lessened the accelerations/decelerations of the kayak): <snip>>>>>>It is not only the stroke rate itself that gives the smoothing benefit. It is the shorter "down-time" between strokes that typically comes with a higher stroke rate.<<<<< I agree with this completely but thought I had already made that point when I quoted from an article I did on paddles: "Reducing the swing weight of the paddle allows a faster transition between strokes. This reduces the amount the kayak must be accelerated during each stroke to recover the speed lost to friction during the interval between strokes. It takes more energy to accelerate a kayak than it does to maintain its speed because now inertia (as well as the already present forces of friction and wavemaking) must also be overcome. The frictional and wavemaking resistances (drag) also are higher with greater variations in speed. The energy savings from the time spent traveling at less than the average speed does not balance the extra energy used travelling at more than average speed. This is partly because frictional resistance increases at nearly the square of the speed. Also, when travelling at or accelerating to the speed where wavemaking resistance becomes a significant factor (around 4 knots for a typical sea kayak) resistance increases at near the fourth power in relation to the speed increase. A more even speed is consistent with the higher paddling cadence that less blade weight allows." Nick continued: >>>>.Imagine two kayaks paddling side by side at the same speed. Guy A has his paddle in the water for 1 second and then out for one second, the Guy B is paddling with in the water for 2 seconds and out for 1. They both will decelerate similarly between strokes, but Guy B will not need to accelerate as much during the time his paddle in the water. As a result he won't need to apply as much force and his stroke will be more efficient.<<<<<, I don't think I can agree with that. Given--for the sake of simplicity--that each paddler keeps his own paddling force equal throughout their stroking time (but not equal between paddlers). They will both need to accelerate up to the same speed again after each one second of rest and deceleration, but guy B will have twice as long to do it so his rate of acceleration will be only half that of guy A's. Guy A will make 6 strokes in 12 seconds while guy B will have only taken 4 strokes to work against the kayaks (same) drag over the same distance at the same speed. Therefore Guy B will be working against the kayaks drag for a total of 8 seconds and have had 4 seconds of rest while guy A will only be working against that same drag for 6 seconds of the 12 and have had 6 seconds of rest between strokes. Guy B only has to accelerate back up to speed 4 times and guy A 6 times in the 12 seconds they traveled the same distance at the same speed. The questions are who is working harder and which strategy is most efficient? I don't know, and unfortunately I'm not up to trying to figure out the math right now, Any of the mathematically adept out there want to give it a shot? More thoughts: Guy A supplies more energy over less time with more rest time and B works longer but at a lower energy rate while he is working. Since it requires the same amount of total energy to work against the same drag for the same distance (if the speed were held constant and if the paddles and strokes have the same efficiency) the differences will have to come from how the acceleration/deceleration factor plays out or possibly whether a short strong stroke is more or less efficient than a longer stroke. There are also limits to how long a stroke can last and still be efficient (personally I think 2 seconds of in water time may be stretching these limits). A one second stroke will be in the most efficient (near perpendicular to the push) position a greater percentage of the stroke time and a shorter harder stroke also seems to me to be more efficient as there isn't so much time for water to "leak" off the paddle into directions other than straight back. I don't know but if I had to bet I'd put my money on the one second stroke time rather than the two second stroke time to take less energy. Also in reality, with a longer stroke time the actual work may be having to be done during a small part of the in water time. In that case the rest of the time the paddle is hanging out in the water is really rest time and deceleration will be occurring then as well. The ideal amount of time to have the paddle in the water (working at a force the paddler can tolerate) will be determined by the time it is operating at high efficiency (moving water straight back rather at some angle-as during the start and finish of a long held stroke such as a sweep stroke for example). Perhaps to avoid this potential confounding we should restate the question so that the longer and shorter stokes would be such that they would be equally distant (in efficiency) from the most efficient stroke rate. That way we would be testing the effect of the ratio (of in water to out of water time) more directly. Nick continued: >>>>>The goal should be to minimize the time your paddle is out of the water while maximizing the "duty-cycle" or the percentage of time the paddle is in the water relative to the full stroke time.<<<<<<< I would agree with the first part of this but would guess that the less time between strokes is much more important than the percentage of time the paddle is in the water vs. in the air. An ergonomic stroke rate that applies the most power during the time the paddle is perpendicular (to the direction of boat travel) with as little time as is practical coasting between the strokes should be the goal (at least if your purpose is to maximize efficiency at fast speeds). "Misisco, David J" <David.Misisco_at_chomp.org> pointed out that there were a lot of variables to control and made that seem to be an insurmountable task to the testing of differences that stroke rates might cause. I disagree. It will depend on the accuracy you need. Many variables must certainly be controlled or corrected for but I think most can be, at least to within a level of accuracy to still allow us to see the differences created by the "tested for" variables that would have any significant effect (such that even a racer would care about them). Ship model testers have been controlling for many of these variables for years (as well as several other variables that wouldn't apply in full size kayak tests). During my own timed (kayak turning and sprint) tests I am careful to record data and note possible confoundings (including the date and location of the tests so I can have a pretty good idea of water temperature and I record if the test was done on salt or fresh water-so I can correct for them. I also note any significant wind (if I couldn't find a place to get out of it to do a test) so I know those "windy" results are less reliable. What I'd really like to do (or induce someone else to do) is to make an electronic paddle shaft (with interchangeable blade capability too) that can measure the force the paddler puts into it accurately and convert this and the data from an accurate knot meter into digital signals that can be recorded synchronistically into a small on-board computer (small analog/digital converter/computer modules exist and are quite low priced now-18 years ago when I first proposed this approach to Sea Kayaker and started to research it they were much more expensive and not integrated into one unit). After controlling most of the variables I think such a device could answer many of our present questions as well as be a great learning aid to help teach paddlers to develop a more efficient stroke. It could also be used to compare kayaks much more realistically than in a towing tank test or the even more removed from reality simulations of towing tank results I do for Sea Kayaker magazine now. For one thing, by measuring the forces going into the paddle we would automatically control for the potentially important variable of yaw (due to the off center propulsion of paddling) which towing tanks totally ignore. It would also account for the speed variation factor discussed earlier. With interchangeable blades we could test and compare the efficiency of different paddle blades as well. I find it hard to believe that the U.S. Kayak Sprint team hasn't done this (or attempted to do this) already but the last time I checked (several years ago) Greg Barton told me they did video motion studies but hadn't yet done a paddle rigged with sensors. If anyone with an engineering bent is interested in developing such a device I would be willing to share what I've researched about the problem already and consult with them on the project. With all the kayaking schools (and tech-weenie kayakers) out there now it might even become a marketable product (if it could be produced for a reasonable price--which I think it could). 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/ ***************************************************************************
At 12:59 AM -0700 7/27/02, Matt Broze wrote: > >Nick continued: >>>>>.Imagine two kayaks paddling side by side at the same speed. Guy A has >his paddle in the water for 1 second and then out for one second, the >Guy B is paddling with in the water for 2 seconds and out for 1. >They both will decelerate similarly between strokes, but Guy B will >not need to accelerate as much during the time his paddle in the >water. As a result he won't need to apply as much force and his >stroke will be more efficient.<<<<<, > >I don't think I can agree with that. Given--for the sake of simplicity--that >each paddler keeps his own paddling force equal throughout their stroking >time (but not equal between paddlers). They will both need to accelerate up >to the same speed again after each one second of rest and deceleration, but >guy B will have twice as long to do it so his rate of acceleration will be >only half that of guy A's. Guy A will make 6 strokes in 12 seconds while guy >B will have only taken 4 strokes to work against the kayaks (same) drag over >the same distance at the same speed. Therefore Guy B will be working against >the kayaks drag for a total of 8 seconds and have had 4 seconds of rest >while guy A will only be working against that same drag for 6 seconds of the >12 and have had 6 seconds of rest between strokes. Guy B only has to >accelerate back up to speed 4 times and guy A 6 times in the 12 seconds they >traveled the same distance at the same speed. The questions are who is >working harder and which strategy is most efficient? I don't know, and >unfortunately I'm not up to trying to figure out the math right now, Any of >the mathematically adept out there want to give it a shot? I did a little analysis in Excel. Bottom line: Guy B (slower cadence,longer stroke, same rest) works less. Obviously, the amount of effort saved depends on drag. With no drag, Guy B applies 75% of the force to maintain the same speed. I haven't worked out the math yet, but this results in the same amount of work. As drag increases the relative force required by Guy B decreases. As drag increases Guy B needs to apply less than 75% of the force while maintaining the same cadence. The advantage accumulates slowly, but it is perceptible. Because Guy B can apply his effort over a longer time he does not need to accelerate the kayak to as high a speed to maintain the same average speed. Since drag increases with speed he is working on moving a boat that has lower average drag. This means less force required and less overall effort. Because the effect is drag dependant (Higher speed -> more efficiency due to longer stroke) the effect will be most pronounced at higher speeds. While Guy B does not get as much rest, he is using less effort to maintain the same speed, so he does not need as much rest. I also ran the analysis with Guy B going at the same cadence as Guy A (ie a stroke every 2 seconds) but with a shorter coasting time. And as expected this saved even more effort than stretching out the stroke. BTW I chose the paddling rates based on being easy to deal with not because they were in any way reasonable. A 2 second long stroke is probably unreasonable, but it is easy to understand. -- 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/ ***************************************************************************
OK, Star Trek was mentioned so the door is open. Gene Roddenberry, creator of Star Trek, was asked how a transporter worked. He said it used a Heisenberg uncertainty compensator. The interviewer asked how the compensator worked. Mr. Roddenberry said, "Very well, thank you." Now THAT is a clear explanation. > You'll have to square this with Star Trek's concept of sub-space before > I'll buy in. (physics - when will it all end????) > > 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/ ***************************************************************************
writes: "Why not paddle in the rain?" Simply put, if it's driven by wind that exceeds your skill and/or tolerance, it's so heavy you can't see your hands, or if you melt in fresh water. Otherwise, it's rather nice. Kevin *************************************************************************** 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: <SNIP>>>>>>>Because Guy B can apply his effort over a longer time he does not need to accelerate the kayak to as high a speed to maintain the same average speed. Since drag increases with speed he is working on moving a boat that has lower average drag. This means less force required and less overall effort.<<<<<< Is this the entire basis for the claims made as the result of the Excel spreadsheet analysis? Why doesn't Guy B have to accelerate to as fast a speed? During the 1 second between strokes a given kayak at a given speed (and all with other variables held constant) is going to slow the same amount and will have to accelerate to the top speed of the previous stroke again to maintain the same average speed (at least it would seem that way to me as long as the acceleration rate was constant throughout both A's and B's stroke. Am I missing something here by trying to do this in my head? If Nick is correct then it will hardly matter to a paddler since the ideal stroke rate will be the one that best finds the point between the stroke being as long as possible vs. it being too long and therefore working at inefficient angles from the direction of kayak motion (the pivoting paddle factor). This would also have to be tempered against the apparently more important factor of being able to minimize the time between strokes. The long stroke may also mean that more distance (time) would have to be covered to get the paddle back into the water again. Also, if the kayaker shifted bodyweight back and forth to make the longer stroke there would be more losses. In either case it would be more efficient to shorten the stroke up some more to maximize the overall efficiency of the stroke. I'm pretty sure that there is something wrong with Peters getting 5% efficiency for a paddle. I like Jeff's addition of paddle slippage speed into the power equation. He wrote: <SNIP>>>>>Thus, the power that a paddler has to put in to keep a constant boat speed is equal to: BOAT_RESISTANCE * (BOAT_SPEED + PADDLE_SLIPPAGE_SPEED) In other words, all other things being equal, greater slippage means more power output by the paddler with no speed advantage.<<<<<Snip> This addition of paddle slippage speed seems to compensate directly for the efficiency factor of the paddle (so you could get the percent of efficiency by dividing that into just the boat speed times the resistance figure. Since the paddle moves very little in comparison to the kayak its efficiency is actually quite high. Mike's example critiquing this while comparing wide and narrow paddles was way out of line in its slippage numbers (having them move twice and 4 times as much as the boat id in the opposite direction) considering the relatively high efficiency for both paddles (but a little higher for the less slippage paddle). The measurement of slippage should also compensate for the lift of a wing paddle (or Greenland paddle if it is acting as a wing like Peter believes). However I don't think it will measure the loss due to drag on the wing as a result of its sideways motion (which is requiring some energy on the paddlers part to move it sideways--that doesn't seem like it will show up as rearward slippage). Maybe this is an area where we need to get into the lift/drag type math Peter was using. We would probably also not be accounting for the energy being wasted in pushing water in directions other than straight back due to the pivoting nature of a kayak stroke (unless we also could measure the total input into the paddle-in which case we could probably skip this slippage measurement altogether in comparing efficiencies). Ignoring the efficiency losses in the human body and the off center location of the pulling point, a perfectly rigid rod at the side of the tank being pulled upon should be 100% efficient at transferring the pullers power output to the kayak. If the center of thrust of a paddle moves as far back through the water as the boat moves forward during the stroke that would be 50% efficiency since you put twice as much in as you get back out in useful work. The rest of the energy didn't disappear it was just lost (for doing useful work) to randomness (or we could substitute "heat" or entropy for randomness). I'm not sure how easily this slippage could be to measured (it is kind of a slippery thing to get a handle on ;-) or even where on the paddle to decide to measure it if we were using, say frames from a video camera to watch and stop the action. We could drop out the time factor (because Distance/Time = Speed and it would be the same interval of time on the video (30 frames per second) and just measure how far the boat went forward and how far the center of thrust on the paddle moved back over the same number of frames (that covered the thrust part of the stroke). By doing this over many strokes and we could likely also include the time between strokes into these efficiency equations. Next question, how can we determine where the center of thrust is on the paddle blade in normal use? Any ideas. Would it bear any relationship to the pivot point in space that will show up on the frame-by-frame screen as a fixed point around which the paddle rotates (in the direction of kayak motion). If so what other points would be involved? I guess I've got more questions than answers again today. 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/ ***************************************************************************
From: "Matt Broze" <mkayaks_at_oz.net> > I'm pretty sure that there is something wrong with Peters getting 5% > efficiency for a paddle. When Peter posted this stuff on Baidarka last year, I asked him to show his work. For example, he calculates 0.4 hp for a Euro paddle. I pointed out that this was quite high and a lower value (based on a discussion I had with John W at the time) was more appropriate. Peter then told me _my_ estimate was too high! However, he has yet to correct for his newer value (which was lower than mine) nor is he willing to reveal that (or any other) part of his calculations. If you pull enough numbers out of your hat, you can prove* anything. Mike *For those not inclined toward math or physics, just be aware that one can use math concepts to prove another math concept but one cannot use math concepts to prove a physical concept. Peter's equations do not represent a proof of anything, just a hypothesis. They require experimental evidence to back them up. When John asked for evidence, he was given a list of textbooks. Fluid mechanics textbooks are filled with theories based on basic concepts derived from studies of flat plates, spheres, cylinders and other simple shapes. Occasionally, a standard NACA foil is used. Kayak and canoe paddles are not representative of these basic shapes and to ensure the appropriateness of the mathmatical models, tests of real paddles must be performed. John and others have done these tests, Peter has not. When I worked on towing tank tests of ice interactions with icebreakers and offshore structures, my boss always told me that if theory agrees with practice by a factor of two, you're doing pretty good. Consider Peter's model in that light. *************************************************************************** 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/ ***************************************************************************
Matt wrote:- >Next question, how can we determine where the center of thrust is on the >paddle blade in normal use? Any ideas. Would it bear any relationship to the >pivot point in space that will show up on the frame-by-frame screen as a >fixed point around which the paddle rotates (in the direction of kayak >motion). G'day Matt and Paddlewise, Wouldn't a paddle fitted with one or two 3 axis accelerometers radio linked to a data logger let you calculate this? And the centre of thrust move in the paddle with time? A friend fitted his paddle with a two axis accelerometer many years ago and still has it available. We're talking about using it with TORSON to simulate the forces involved in kayak injuries but I think 3 axis will be necessary. I'm told this has already been done for rowing and running. Has it been done for kayaking? All the best, PeterO *************************************************************************** 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/ ***************************************************************************
Matt wrote, >I'm not sure how easily this slippage could be to measured (it >is kind of a slippery thing to get a handle on ;-) or even where on the >paddle to decide to measure it if we were using, say frames from a video >camera to watch and stop the action. G'Day Matt and Paddlewise, To a very very rough approximation, not taking account of chaotic local behaviour of paddled water, could slippage be measured either by repeatedly moving a paddle in a tank or in a current free lake and having a floating line with equispaced markers tightly stretched along the paddle route and videoing the progress of the paddle relative to the markers? Possibly put a set of colored rings along the shaft of the paddle where it enters the water to help. The test paddler might need a rudder to paddle in a sufficiently straight line:~) Expect this has been thought of and rejected for various reasons - but still curious? All the best, PeterO *************************************************************************** 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 O wrote: <SNIP>>>>>>Wouldn't a paddle fitted with one or two 3 axis accelerometers radio linked to a data logger let you calculate this? And the centre of thrust move in the paddle with time? A friend fitted his paddle with a two axis accelerometer many years ago and still has it available. We're talking about using it with TORSON to simulate the forces involved in kayak injuries but I think 3 axis will be necessary. I'm told this has already been done for rowing and running. Has it been done for kayaking?<<<<<<SNIP> Actually, years ago when I was working on this problem for John Dowd and John Dawkins when Sea Kayaker was first thinking of doing kayak reviews (1985) I wanted to put two strain gauges at 90 degrees to each other on each side of the paddle shaft (between hands and the blade-4 strain gauges in all). This should tell you the total force going into the paddle and its direction of application too. What it couldn't tell you was if paddlers (or a single paddler) was using a consistent stroke so in order to confirm the accuracy of the results (and so the test paddler couldn't cheat on the test without the testers knowing about it) I also looked into the kind of devices that would measure rotations around each axis in order to know exactly where the paddle was at all times. If I recall correctly besides the weight, bulk and high price these items were then there also might have been a problem with how fast they could detect and output data and their "slew" rate. Maybe they are all small and light, fast, cheap and solid state now and we could employ them to assure consistency of stroke (and for training) as well as the strain gauges in our new test platform paddle. I know the analog/digital converter and computer and storage of data have all been integrated into a small and relatively cheap device since all being separate when I looked into them back in 1985 or 86. I'd like to hear about what your friend's paddle can do and more about why he did it. I'm unaware of anyone doing this but suspect the U.S. Sprint team would if anyone would have. I'll try to remember to ask Greg Barton about it next time I talk to him. He's an engineer, makes paddles and already has a distribution network and contacts with a lot of racers. I'll bet he is real interested in the subject himself too. This kind of thing should be right up his alley. Maybe I can get him interested in working on this. I'd sure like to play with this kind of paddle. I think now most paddle experiments are done by dragging paddles at a fixed angle through a water tank and since this isn't rally how a paddle is used it would be better to have an electronic paddle that you use like any other paddle while it measures angles and forces every 1/10 of a second or so. Run a knotmeter into the same computer and I think you could find out about the efficiencies of blades, boats and paddlers by controlling the other variables and measuring the effects of the one you are studying at the time. Imagine being able to paddle different boats into the same head seas and wind and comparing there performance with each other and with their calm water performance. Considering the possibilities for improving the efficiency of paddler, paddle and boat I can't believe the U.S. Sprint team hasn't tried to do this already. Peter asked: <SNIP>>>>>>...could slippage be measured either by repeatedly moving a paddle in a tank or in a current free lake and having a floating line with equispaced markers tightly stretched along the paddle route and videoing the progress of the paddle relative to the markers? Possibly put a set of colored rings along the shaft of the paddle where it enters the water to help.<<<<SNIP> That would be easy. Put bright targets on the paddle shaft and blade edge and using frame by frame stop action play of the video you could measure the distance and the speed of the kayak with grease pencil marks right on the TV screen. What I've yet to figure out is where along the paddle shaft do we make the measurement that determines how much the paddle has slipped. Assuming it is at the center of thrust (or even average center of thrust) on the blade how do we find out where that is along a vertical axis so we can measure the slippage distance of the paddle at that depth (or average depth) on the TV screen. Ralph, I was at the 1982 and 1984 LL Bean Symposiums. This kind of rings a bell. Maybe that was me asking Derek about the practicality of seal landings. The seal landing possibilities were a standing joke with Cam and I whenever we looked at a swell washed shore during our paddles together on the ocean coasts of WA and BC. I don't recall Derek getting hurt though, but then I might not have been paying attention and missed it. 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/ ***************************************************************************
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