A week ago, in a class, the instructor talked about placing the paddle in the water at your toes, and removing it from the water at your hip. He gave a quick explanation of the physics of taking it out at the hip rather than a longer follow through, then went on to another topic. I meant to ask him about it back at the take-out, but forget, now I can't even remember the quick explanation. So.... what are the physics here? Why do you lose efficiency if your stroke extends past your hip? It was something about water compression versus lift????? Rick - 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/ ***************************************************************************
At 09:55 AM 6/13/01 -0400, Rick Sylvia wrote: >A week ago, in a class, the instructor talked about placing the paddle in >the water at your toes, and removing it from the water at your hip. He gave >a quick explanation of the physics of taking it out at the hip rather than a >longer follow through, then went on to another topic. I meant to ask him >about it back at the take-out, but forget, now I can't even remember the >quick explanation. > >So.... what are the physics here? Why do you lose efficiency if your stroke >extends past your hip? It was something about water compression versus >lift????? Did the instructor also cover the sweep stroke? When doing a sweep stroke the most effective part of the stroke is the last half. If you're doing a forward sweep, the greatest turning motion is achieved when the paddle blade is the water from about the cockpit back towards the stern. Unless you're keeping your paddle very close to the hull during the forward stroke you're going to be turning the boat more if you keep the blade in longer if it goes much past your hip instead of just propelling it forward. Have you ever watched a real beginner that is having trouble keeping the boat going in the direction they want. Usually, they're always turning to the left (often because the angle of the blade on the left is tilted forward more than on the right). They'll try to correct by paddling more on the left side but they're usually very short strokes from about their knee to the cockpit. They're getting very little turning motion because the paddle never goes back towards the stern with a nice arc so they keep on going in the same direction to the left of their desired course. Making a wider arc with the paddle and extending the stroke farther back will result in more turning motion. Keeping it close to the hull, and stopping it before it starts turning the boat will more efficiently paddle the boat forward in the same direction. *************************************************************************** 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:"Rick Sylvia" <Rick.Sylvia_at_ferginc.com>; <paddlewise_at_paddlewise.net> >So.... what are the physics here? Why do you lose efficiency if your stroke >extends past your hip? It was something about water compression versus >lift????? The idea is that the direction of the power face gets more "up" than "back" once the blade passes your hip. Hence you're lifting the water more than pushing yourself forward. 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/ ***************************************************************************
From: "John Fereira" <jaf30_at_cornell.edu> > > Did the instructor also cover the sweep stroke? When doing a sweep stroke > the most effective part of the stroke is the last half. If you're doing a > forward sweep, the greatest turning motion is achieved when the paddle > blade is the water from about the cockpit back towards the stern. I know one BCU instructor that states quite emphatically that this is completely wrong. He says that the water is too turbulent near the rear of the hull for the stroke to be effective and insists you stop just past the hip. I think he's wrong, IMNSHO, because the turbulent water is very close to the kayak and you'd have to whack the kayak with the blade to get into that region. Personally, I have a real problem with all these explanations. If you do a sweep stroke from the torso, with hands low (paddle shaft close to horizontal) and in a more or less static position relative to the body, you are applying a constant moment (torque)* that will turn the kayak regardless of the point where the paddle is inserted! Or to get to the point, the stroke is just as effective in turning at the front as at the back. I wonder if the illusion that the power is at the back comes from the fact that the beginning of the stroke uses power to accelerate the kayak, while the later part of the sweep just maintains the rotation speed? I always do a sweep with a full rotation (as close to 180 degrees as I need) and often do a return stroke as a low brace. The latter keeps me confident if on a hard edge. Mike *Technically, this is a wrench rather than a moment. You are generating a moment and a linear force simultaneously. In this case, the linear force changes direction continously, so you slide away from the stroke side of the kayak at the start of the stroke, forward in the middle of the stroke and toward the stroke side at the end, assuming you go roughly 180 degrees. *************************************************************************** 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/ ***************************************************************************
Michael Daly wrote: > > From: "John Fereira" <jaf30_at_cornell.edu> > > > > Did the instructor also cover the sweep stroke? When doing a sweep stroke > > the most effective part of the stroke is the last half. If you're doing a > > forward sweep, the greatest turning motion is achieved when the paddle > > blade is the water from about the cockpit back towards the stern. > > I know one BCU instructor that states quite emphatically that this is completely > wrong. He says that the water is too turbulent near the rear of the hull for the > stroke to be effective and insists you stop just past the hip. I think he's wrong, > IMNSHO, because the turbulent water is very close to the kayak and you'd have > to whack the kayak with the blade to get into that region. I think the the potential increase in cadence is a far better argument than turbulence, lift, whatever. > > Personally, I have a real problem with all these explanations. If you do a sweep > stroke from the torso, with hands low (paddle shaft close to horizontal) and in a > more or less static position relative to the body, you are applying a constant > moment (torque)* that will turn the kayak regardless of the point where the paddle > is inserted! Or to get to the point, the stroke is just as effective in turning at the > front as at the back. and now for something completely different- I was taught (ACA/BCU) the the primary sweep power is at the bow til 2:00, forward from 2-4:00, then strong sweep from 4-6:00. the best way to do this is as you express in the next quote: > > I always do a sweep with a full rotation (as close to 180 degrees as I need) and > often do a return stroke as a low brace. The latter keeps me confident if on a > hard edge. with the addition of that nice skimming brace that I was introduced to just last year. > > Mike > > *Technically, this is a wrench rather than a moment. You are generating a moment > and a linear force simultaneously. In this case, the linear force changes direction > continously, so you slide away from the stroke side of the kayak at the start of the > stroke, forward in the middle of the stroke and toward the stroke side at the end, > assuming you go roughly 180 degrees. > > *************************************************************************** > 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/ > *************************************************************************** -- ¤ Gabriel L Romeu ¤ http://studiofurniture.com + /diary or + /paint *************************************************************************** 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: "Michael Daly" <michaeldaly_at_home.com> > Michael Daly wrote: > *Technically, this is a wrench rather than a moment. You are generating a moment > and a linear force simultaneously. I woke up this morning and said to myself "This is wrong!" It's not a wrench, it's a pure moment generated by the torso muscles. I was thinking backwards when I wrote it. > the linear force changes direction > continously, so you slide away from the stroke side of the kayak at the start of the > stroke, forward in the middle of the stroke and toward the stroke side at the end, > assuming you go roughly 180 degrees. This part is still true though. 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/ ***************************************************************************
From: "Gabriel L Romeu" <romeug_at_erols.com> > Michael Daly wrote: > > > > From: "John Fereira" <jaf30_at_cornell.edu> > > > > > > Did the instructor also cover the sweep stroke? When doing a sweep stroke > > > the most effective part of the stroke is the last half. > > > > I know one BCU instructor that states quite emphatically that this is completely > > wrong. > > I think the the potential increase in cadence is a far better argument > than turbulence, lift, whatever. Are you worried about cadence in a sweep? One long sweep wastes less time that two short ones if you really, really, really need to change direction. > > > > Personally, I have a real problem with all these explanations. If you do a sweep > > stroke from the torso, with hands low (paddle shaft close to horizontal) and in a > > more or less static position relative to the body, you are applying a constant > > moment (torque) that will turn the kayak regardless of the point where the paddle > > is inserted! Or to get to the point, the stroke is just as effective in turning at the > > front as at the back. > > and now for something completely different- I was taught (ACA/BCU) the > the primary sweep power is at the bow til 2:00, forward from 2-4:00, > then strong sweep from 4-6:00. Now is that based on the biomechanics (i.e. the muscle action) of the stroke (something I completely, and deliberately ignored in my statement)? It sounds like it's based on the misconception that the blade direction and nearness to the ends of the kayak generate the turning moment. Imagine that you are the kayak and you feel something making you turn. What is it? You can't see the paddle so you don't know about it. All you feel is the paddler's backside, hips, knees/thighs and feet. What does it matter where the paddle is? All the paddle forces feed back through the paddler into the kayak. Unless there's a reason that the paddler is doing better (- the biomechanics I'm ignoring for lack of knowledge) the paddle orientation in a uniform sweep is irrelevant. It is possible that they are taking issue with the fact that the central portion of the sweep generates the most forward motion in addition to the turning. > > > > > I always do a sweep with a full rotation (as close to 180 degrees as I need) and > > often do a return stroke as a low brace. The latter keeps me confident if on a > > hard edge. > > with the addition of that nice skimming brace that I was introduced to > just last year. I learned it last year as well and it was one of those "Duh, why didn't I think of that?" It's so obvious, but I never did it. Skimming is the key word of course. I like it in part because it reminds me of the gentle Canadian stoke I used to use canoeing in days gone by. 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/ ***************************************************************************
I've read about folks using Greenland style stroke variations with non-Greenland style paddles; These folks reported positive results. I have not tried it myself, however. Craig ----- Original Message ----- From: "Gabriel L Romeu" <romeug_at_erols.com> To: <gstamer_at_magicnet.net> Cc: <paddlewise_at_paddlewise.net> Sent: Thursday, June 14, 2001 9:20 PM Subject: Re: [Paddlewise] "Regular" paddle stroke > Nevertheless, an interesting observation and worthy of some experiment. > Greg Stamer wrote: > > > > > I don't know how well these techniques apply to paddles other than Greenland > > "sticks". *************************************************************************** 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/ ***************************************************************************
Michael Daly wrote: > > > > I think the the potential increase in cadence is a far better argument > > than turbulence, lift, whatever. > > Are you worried about cadence in a sweep? One long sweep wastes less time > that two short ones if you really, really, really need to change direction. Oddly, this was referring to an earlier part of the message dealing with the turbulence factor in pulling the paddle beyond the hip in the forward stroke (as in the subject line)- don't know how it got there. Thanks for the observation. -- ¤ Gabriel L Romeu ¤ http://studiofurniture.com + /diary or + /paint *************************************************************************** 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/ ***************************************************************************
Michael Daly wrote: > > > and now for something completely different- I was taught (ACA/BCU) the > > the primary sweep power is at the bow til 2:00, forward from 2-4:00, > > then strong sweep from 4-6:00. > > Now is that based on the biomechanics (i.e. the muscle action) of the stroke > (something I completely, and deliberately ignored in my statement)? It sounds > like it's based on the misconception that the blade direction and nearness to the > ends of the kayak generate the turning moment. > > Imagine that you are the kayak and you feel something making you turn. What is > it? You can't see the paddle so you don't know about it. All you feel is the paddler's > backside, hips, knees/thighs and feet. What does it matter where the paddle is? > All the paddle forces feed back through the paddler into the kayak. Unless there's > a reason that the paddler is doing better (- the biomechanics I'm ignoring for lack of > knowledge) the paddle orientation in a uniform sweep is irrelevant. Michael makes an excellent point about the blindness of the kayak. It doesn't know where the paddle is, it just reacts to the forces exerted by your butt, knees, and feet. I have noticed that when my sweep doesn't seem to be working, it's because I'm thinking about what my paddle is doing (really, it's not doing anything, just pressing against the water) and not my knee, which is what actually turns the boat. As to the sweep, the biomechanics really can't be ignored. I've just been gedankening around here in my swivel chair. If I rotate forwards and grab then corner of the desk, I can spin myself around very forcefully...Wheeee...Uh, oh, wait a minute until the vertigo passes.... Yes, well, as I was saying, if I now reach straight out to the side and try to spin the chair, it's much less forceful, as I can't recruit the torso nearly as much. Before you bring it up, yes, I do know the difference between an office chair and a kayak; the latter is more comfortable. :) -- Steve *************************************************************************** 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 Sat, 16 Jun 2001, Gabriel L Romeu wrote: > Steve Cramer wrote: > > Michael makes an excellent point about the blindness of the kayak. It > > doesn't know where the paddle is, it just reacts to the forces exerted > > by your butt, knees, and feet. > > This is just speculation, but I think you would be correct if we were > paddling a spherical object in the water. I'm not sure I can see the sequitur. A spherical kayak is blind to what the paddle is doing, but our long skinny ones are not? I'm not disagreeing with what you said (which I have snipped). I was just making the point that our bodies move the boat, not the paddle. Certainly, different hull shapes, either static or dynamic (as by heeling) make it easier or harder to do so. Steve Cramer *************************************************************************** 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/ ***************************************************************************
I agree with you Steve, but the effect of the stroke throughout the sweep may not be uniform on the motion of the kayak. Probably the reference should have been under a previous statement rather than yours. Steve Cramer wrote: > > On Sat, 16 Jun 2001, Gabriel L Romeu wrote: > > > Steve Cramer wrote: > > > Michael makes an excellent point about the blindness of the kayak. It > > > doesn't know where the paddle is, it just reacts to the forces exerted > > > by your butt, knees, and feet. > > > > This is just speculation, but I think you would be correct if we were > > paddling a spherical object in the water. > > I'm not sure I can see the sequitur. A spherical kayak is blind to what > the paddle is doing, but our long skinny ones are not? I'm not disagreeing > with what you said (which I have snipped). I was just making the point > that our bodies move the boat, not the paddle. Certainly, different hull > shapes, either static or dynamic (as by heeling) make it easier or harder > to do so. > > Steve Cramer > -- ¤ Gabriel L Romeu ¤ http://studiofurniture.com + /diary or + /paint *************************************************************************** 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: "Gabriel L Romeu" <romeug_at_erols.com> > Steve Cramer wrote: > > > > On Sat, 16 Jun 2001, Gabriel L Romeu wrote: > > > > > Steve Cramer wrote: > > > > Michael makes an excellent point about the blindness of the kayak. It > > > > doesn't know where the paddle is, it just reacts to the forces exerted > > > > by your butt, knees, and feet. > > > > > > This is just speculation, but I think you would be correct if we were > > > paddling a spherical object in the water. > > > > I'm not sure I can see the sequitur. A spherical kayak is blind to what > > the paddle is doing, but our long skinny ones are not? > > I agree with you Steve, but the effect of the stroke throughout the > sweep may not be uniform on the motion of the kayak. > Just a note. The forces and moments in a sweep are mutually orthogonal. That is, they are independent and their effects are independent. The moments cause turning. The forces cause translation (linear motion). These forces and moments act through the paddler at the center of the kayak, not where the blade touches the water. My point made way back when was that the turning effects are not dependent on the location of the paddle blade (give or take biomechanical effects). Niels brought to our attention the importance of the translation to certain paddlers, such as slalom kayakers. He also pointed out that the linear forces when the paddle blade is drawn toward the kayak at the rear can contribute to the kayak's stern yawing in a skid. I think, in the end, that several different correct points have been made. As you say, the motion is not uniform, even if the turning is. In a full sweep, the lateral translations can cancel out, while the longitudinal translation results in a net forward motion. That's why you need alternate forward and reverse sweeps on opposite sides of the kayak to do a 360 in a tight spot (cancel the longitudinal motions). As long as paddlers can keep these concepts straight, I'm happy. If they don't and start coming to ridiculous conclusions, I get cranky. That's because I'm one of those fastidious engineer types. 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/ ***************************************************************************
Gabriel L Romeu wrote: > > I agree with you Steve, but the effect of the stroke throughout the > sweep may not be uniform on the motion of the kayak. > > Probably the reference should have been under a previous statement > rather than yours. Oh. perhaps so. Now I understand better what your meant by "speherical" > > Steve Cramer wrote: > > > > On Sat, 16 Jun 2001, Gabriel L Romeu wrote: > > > > > Steve Cramer wrote: > > > > Michael makes an excellent point about the blindness of the kayak. It > > > > doesn't know where the paddle is, it just reacts to the forces exerted > > > > by your butt, knees, and feet. > > > > > > This is just speculation, but I think you would be correct if we were > > > paddling a spherical object in the water. > > > > I'm not sure I can see the sequitur. A spherical kayak is blind to what > > the paddle is doing, but our long skinny ones are not? I'm not disagreeing > > with what you said (which I have snipped). I was just making the point > > that our bodies move the boat, not the paddle. Certainly, different hull > > shapes, either static or dynamic (as by heeling) make it easier or harder > > to do so. *************************************************************************** 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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