John Gibbs wrote: "After a couple of weeks' paddling ... I received shipment of an Eddyline Midswift paddle. It's nice and light, and I like the blade size, but I notice a fairly pronouced flutter..." I don't pretend to be an expert on this, but here's what I heard about paddle flutter from a U.S. national whitewater slalom kayak team member: (Assuming the paddle is not defective in design or manufacture,) the primary cause of paddle flutter is cavitation, i.e. the formation and separation of bubbles at the back of the blade as it is drawn through the water. Lightweight, thin blades tend to be more prone to flutter than thicker, heavier blades. Cavitation reduces the efficiency of the paddle stroke, so racers try to reduce cavitation as much as possible. The technique that they practice involves, at the beginning of the stroke, emphasizing sliding the blade into the water along its axis ("spearing the fish"). My own, limited experience bears this out. When the entire stroke is one long drawing motion, there is pronounced flutter in any of the lightweight paddles that I have used over the years; when I emphasize a sliding/stabbing blade entry, transitioning to a pulling effort as the blade becomes fully immersed , flutter becomes negligible. If I again experience flutter, typically when exerting maximum effort, it's a signal that my stroke has deteriorated and I need to make a technical adjustment. Mike VandammGreenbelt, Maryland USA(If anyone can tell me how to prevent Hotmail from eliminating paragraph breaks in my posts to this list, please send advice to mvandamm_at_hotmail.com.) ------------------------------------------------------------------------ Get your FREE download of MSN Explorer at http://explorer.msn.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 10:26 AM -0500 11/30/01, Michael Vandamm wrote: ><snip> the >primary cause of paddle flutter is cavitation, i.e. the formation and >separation of bubbles at the back of the blade as it is drawn through the >water. Lightweight, thin blades tend to be more prone to flutter than >thicker, heavier blades. Cavitation reduces the efficiency of the paddle >stroke, so racers try to reduce cavitation as much as possible. <snip> The correct term is "ventilation" not "cavitation". Ventilation is air brought down from the surface. Cavitation is a bubble produced by a blade moving with such force that a vacuum appears behind the blade. This happens with high speed motor boats and submarines, but is impossible for a kayaker to produce. Cavitation is what produces the pitting on outboard motor propeller blades. The collapse of the cavitation bubble releases a lot of energy which eventually eats into the propeller. The technique of spearing the paddle into the water will help reduce ventilation as it reduces the amount of air from being pulled down during the stroke. However, this is not a cure for flutter which can happen with or without ventilation. And ventilation may occur with paddles that show no sign of flutter. Ventilation is a bad thing in that you are moving air instead of water. And like paddling without touching the water, moving air is not as efficient as moving water. Nick -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
From: "Michael Vandamm" <mvandamm_at_hotmail.com> > I don't > pretend to be an expert on this, but here's what I heard about paddle > flutter from a U.S. national whitewater slalom kayak team member: > (Assuming the paddle is not defective in design or manufacture,) the > primary cause of paddle flutter is cavitation, i.e. the formation and > separation of bubbles at the back of the blade as it is drawn through the > water. This isn't correct. Cavitation is not easy to create with a paddle, as it requires a significant pressure drop across the blade. He's confusing it with ventilation, where air is dragged into the water when the blade is inserted. But he's still not completely correct. The flutter is caused by Karman vortex shedding. These vortices can form regardless of whether or not they are ventilated, so that bit is irrelevant. Karman vortex shedding is a form of instability where a vortex is spilled alternatively off of one and then the other side of the blade. My own experience is that these _seem_ to be independent of the formation of large vortices on both sides of the paddle. There is no visual indication that the large, roughly symmetric vortices change in sync with the period of the Karman vortices. However, I think that this may simply be due to the fact that I can't visually detect the changes. It seems true that the Karman vortices are superimposed on the ventilated vortices and they occur independantly. Getting rid of the ventilation doesn't guarantee that either vortex is eliminated, just that they become harder to see. Tilting the blade enough will eliminate the symmetry and reduce the problem, as some have suggested. This, however, sounds like the wrong approach IMHO. Good paddles don't have objectionable flutter even if drawn straight through the water. There is something else happening to John's paddle. Since others have reported that their Eddyline MidSwift paddles don't have this problem, either the paddle is defective, or John is doing something to aggrevate the problem. Sitting here, I don't know what the answer is. 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/ ***************************************************************************
At 12:56 PM -0500 11/30/01, Michael Daly wrote: >Snip> >Tilting the blade enough will eliminate the symmetry and reduce the problem, >as some have suggested. This, however, sounds like the wrong approach >IMHO. Good paddles don't have objectionable flutter even if drawn straight >through the water. There is a good explanation of the benefit of angling the blade slightly at: http://courses.washington.edu/phys208/notes/lect19.html Summarizing: There will always be two matching vortices (to conserve angular momentum). Angling the blade causes one vortex to spin free while the other causes rotation of water around the blade. Since this second vortex around the blade effects a greater mass of water than if it were spinning free (as it would in an un-angled blade) it is more efficient. This efficiency is due to the principle that pushing a large mass of water slowly is more efficient than moving a small mass rapidly. I think that the reason most people don't experience flutter is they unconsciously angle the blade slightly, either that or they keep the force down below the range where it creates vortex shedding, again unconsciously. The people I've talked to who had problems with paddle flutter usually report it goes away seemingly of its own accord. Since it is unlikely the paddle got better, it is more likely they adjusted their technique without knowing it. Nick -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
In a message dated 12/2/01 6:03:57 PM, michaeldaly_at_rogers.com writes: << I can't help but notice that the vendors on this list tend to recommend changing the paddler rather than the gear - or is that my imagination :-) I'd hope experience would suggest changing gear rather than changing gear without the background to know what to change to. I like the advise I see here. <<PPS - I do get my back up when misquoted. A couple of times in this thread folks have suggested I said that paddles shouldn't flutter. In fact I have repeated that all paddles flutter, but some are better than others. I apologize if I have offended anyone with the apparent sharpness of my responses. >> I'd suspect everyone gets a bit head-up when pulled the wrong way. Technical discussions like this seem to generate the most hear just because those of you with "professional" experience seem to have the most invested in the exact words you post and the specific meaning you have for them. Me, I haven't any idea what lift or whatever forces you are talking about mean. I just know I need to reach a tad more and it stops annoying. Thanks to all who attempt to enlighten folks like me. Joan *************************************************************************** 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/ ***************************************************************************
Here are the results of a couple hours' experimentation with the Eddyline Mid Swift paddle and its flutter, taking into account some suggestions made here. * Varied the power of the stroke from very light to aggressive: little difference. Actually, with a strong stroke sometimes the flutter diminished, but this was probably because of the strong grip I tended to exert. I controlled for this variable by maintaining a looser grip, and the flutter remained fairly constant. * Angled the top of the paddle blade back a degree or two, remembering Nick Shade's description of the angle providing lift, but fogetting he said to tilt the top back (a forward tilt would seem to me to be pulling the boat down rather than providing lift ??). Anyway, the forward tilt certainly seemed inefficient and contrary to the way the blade wanted to pull, as Mike McNally mentioned. (Mike, which way did you twist the blade to control flutter?) * Inserted the paddle as vertically as possible while moving at very slow speed and allowed time for any trapped air to surface, then stroked: no change in flutter. I doubt it would be considered a manufacturing defect, because the effect is entirely symmetrical, and right and left blades for this paddle have got to be separate molds. Joe Pylka mentioned flutter is greater when the shaft extends well into the length of the blade. This is the case with the Swift; the shaft protrudes from the back of the blade by a thickness of about 2.5 cm+ at the near end of the blade down to 1 cm, ending only about an inch from the far edge of the blade. I don't know how much this varies among paddles. I wonder if I'm facing a traceoff between flutter and a heavier paddle. I don't know if this is a performance drag, but it might be worth a few oz. of extra weight over the approx. 29 oz of the Swift to eliminate this distraction. I'm minded to return the paddle, if PacWave (www.pacwave.net) will allow it, and try something else. Experimenting with equipment is part of the pleasure, especially when I get such in-depth commentary from my experienced colleagues here. *************************************************************************** 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 Sun 02 Dec 2001, John Gibbs wrote: > McNally mentioned. (Mike, which way did you twist the blade to control > flutter?) I don't recall. And I didn't mean to say that tilting forward was bad (if done in moderation to reduce flutter) it just seemed an appropriate segway to wing paddles. Theoretically it would be better to reduce flutter by tilting the top of the blade/shaft back so as to add lift rather than pulling the boat into the water, but it could have been the other rotation that worked better. i And when using a light grip a little flutter is probably acceptable. That's where the only real test of the paddle is a comparison. 'Cause all paddles flutter (I presume from what others here have said). -- Mike McNally mmcnally3_at_prodigy.net *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
> >* Angled the top of the paddle blade back a degree or two, remembering Nick >Shade's description of the angle providing lift, but fogetting he said to >tilt the top back (a forward tilt would seem to me to be pulling the boat >down rather than providing lift ??). Anyway, the forward tilt certainly >seemed inefficient and contrary to the way the blade wanted to pull, as Mike >McNally mentioned. (Mike, which way did you twist the blade to control >flutter?) It may seem contrary to good practice to tilt the top of the blade forward (towards the bow), but this actually makes it work more like a wing paddle. With a forward tilt, the blade will tend to slice deep and cleanly as you place it into the water. Then as the stroke progresses, the top edge becomes the leading edge as the blade moves slightly away from the boat. The result is the lift power is parallel to the direction you are trying to move and it does not pull the boat down much. There is a decent description of wing paddle technique at http://www.sfdj.com/fall/freedive/technique.html and at http://www.bcu.org.uk/marathon/kayak_tech.htm. The wing paddle tends to do this technique some what naturally. You can find similarities in the Greenland technique described at http://www.jacksonville.net/~dldecker/fskaGreenland.htm The technique feels odd at first because the grip on the water at the beginning of the stroke is slippery with the blade tending to dive. But with a little torso rotation the power phase is very natural, easy and powerful. The forward tilt reduces the ventilation at the beginning of the stroke because the paddle slices in and it reduces flutter because the vortex is force to stay on one edge. And the efficiency of the stroke is increased because you end up pulling against a larger mass of water. -- 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/ ***************************************************************************
This message apparently didn't get trough the first time or was intercepted or delayed due to a v warning also included so I'll try sending it with the warning edited out. I usually explain paddle flutter as the "falling leaf effect" rather than "alternate vortex shedding". Most have folks have seen how a falling leaf reacts to a force (gravity) in a fluid (air). One thing no one mentioned was that in general the narrower the paddle blade the higher the flutter rate. I find a high rate of flutter unacceptable because I never know where the paddle blade is going to be if it is fluttering too fast. Some blades certainly flutter less than others and some paddles are harder to control (the flutter) because of things like round (non-ovalled) grips, too narrow a shaft, and/or too much distance to the blade from your hand. I find that using a "wing paddle" type paddle stroke (sliding the blade out to the side as the stroke progresses) virtually eliminates paddle flutter even on hard accelerating strokes. Yes, one can control it by gripping the paddle tighter and working against its direction (if it is slow enough) but why waste the effort. I'd rather hold the paddle looser and not fight the flutter if it is relatively slow. Maybe there is even a "lift" effect gained by flutter. Paddle Peter Chopelas might be able to enlighten us about this. 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/ ***************************************************************************
I usually explain paddle flutter to customers as the "falling leaf effect" rather than "alternate vortex shedding". Most have seen how a falling leaf reacts to a force (gravity) in a fluid (air). One thing no one mentioned was that in general the narrower the paddle blade the higher the flutter rate. I find a high rate of flutter unacceptable because one never knows where the paddle blade is going to be if it is fluttering too fast. Some blades certainly flutter less than others and some paddles are harder to control (the flutter) because of things like round (non-ovalled) grips, too narrow a shaft, and/or too much distance to the blade from your hand. I find that using a "wing paddle" type paddle stroke (sliding the blade out to the side as the stroke progresses) virtually eliminates paddle flutter even on hard accelerating strokes. Yes, one can control it by gripping the paddle tighter and working against its direction (if it is slow enough) but why waste the effort. I'd rather hold the paddle looser and not fight the flutter if it is relatively slow. Maybe there is even a "lift" effect gained by flutter. Paddlewiser Peter Chopelas might be able to enlighten us about this. However, he may be busy right now fighting a new and dangerous virus his computer sent to mine (one with a hidden attachment that automatically takes one to the open attachment screen--which then might easily be accidentally opened if the e-mail comes in while one is typing away at another e-mail and activates the default choice--as has happened to me several times recently causing me to have to retype whole passages). I tried to warn him about the virus but the e-mail I replied with bounced back to me. Perhaps he will see this. 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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