Little whirlpools on each paddle stroke

7 years 6 months ago #19994 by Ric
As the title says... Good or bad? :S

I've been practising Oscar's stroke exercises while standing in the pool.

Depending on how I take the stroke, I get little whirlpools formed on each paddle stroke, that "roll" their way past me. When doing the same in the boat, they "roll" down the side of the boat.

On a beautiful flat sea paddle yesterday, it seemed I could modify my catch to get them at the catch (or to not)...


So is that the sign of better or worse technique? Should I take them as a good sign to practice with, or a bad sign to never ever
do?


'Whirlpools?' 'Rolling past a boat?' What madness am I talking?!? Is this really a surfski forum :whistle:

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7 years 6 months ago - 7 years 6 months ago #19996 by foundwood
I ripped this picture off of the internet and it shows exactly the whirlpools we see coming off of our wing paddles, except this is from an airplane:



You are not discussing madness. This is physics and science and all of those wonderful reactions and forces that we marvel at and play with but do not fully understand...
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7 years 6 months ago #19997 by Physio
yes but aeroplanes put winglets to get rid of them, so to the first question, good or bad?




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7 years 6 months ago #20003 by Kayaker Greg
Your going to get them in the pool as you are moving the paddle through the water, however when you are on your ski I think you should be trying to eliminate the blades movement through the water as its the ski you want to be moving through the water, so minimizing the whirlpools with a good catch would be a good thing to aim for. Off course there maybe some whirlpools from moving the blade out to the side? Can't say I've noticed because looking down at the blade as I paddle ruins the stroke.

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7 years 6 months ago #20004 by Marieski
Damn! And I thought they just bent the wings up so they could fit the planes in the hangar.

Past skis: Spirit PRS, EpicV10Sport Performance, Epic V10 Elite, Stellar SES Advantage. Current skis: Fenn Elite Spark, Fenn Swordfish vacuum. Custom Horizon, Epic V7

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7 years 6 months ago #20006 by Jmuzz
Whirlpools in the water is probably of fairly little importance in technique analysis.
A coaches eye for 30 seconds will probably pick up many higher priority issues above the waterline for you to concentrate on.

In a sea kayak I play with making the biggest whirlpools as I can while waiting for people. Especially interesting when there are jellyfish around and you can get them sucked into the vortex and spinning.

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7 years 6 months ago #20007 by Kayaker Greg
Disagree, a good catch is the most important component and the rest of the stroke follows from there, there is a lot of variation in technique but without a good catch you will be crap no matter what it looks like.

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7 years 6 months ago - 7 years 6 months ago #20008 by Ric

Kayaker Greg wrote: you are moving the paddle through the water


As you point out, we move it out to the side. This is one way I can create these whirls, they almost seem to roll off the blade as it sweeps out.

Also at the catch, you move the blade in the water.


Kayaker Greg wrote: Can't say I've noticed because looking down at the blade as I paddle ruins the stroke.


I hear you. If you wanted to see, take a good solid explosive-catch stroke, and as you exit the blade have a look down and back.


Kayaker Greg wrote: a good catch is the most important component


agreed and that's actually what prompted this post of mine - catch training on Saturday on the pond we call False Bay.

Oscar's catch style of spearing the paddle in - not much whirlpool. But then there is no force being applied until the blade is fully sunk.

Tim Brabants style of catching with force got some whirlpool effects. Now I'm no Dr Tim, but it prompted me to wonder.

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7 years 6 months ago #20009 by Kayaker Greg
Something that was pointed out to me after attending Oscars clinic and having questions afterwards, you will find that the technique used by and for an Olympic sprint race will be quite different to the technique used for a long distance ski race. Remember Oscars statement that he never paddles up wind and only ever practices technique or paddling downwind. Now look at what your interest is and make adjustments as for what works for what you are doing. The rate a sprint paddler turns over a paddle could be twice or more that of a ski paddler, the catch and more will be different.

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7 years 6 months ago #20011 by fredrik
According to the "books" the wing paddle is supposed to be locked in the water and the boat moves forward relative to the locked paddle.

I have difficulty believing that this is the absolute picture. If the paddle is locked with a - say - medium paddle (no slippage in the water, just the outward movement) then it should not be any more hard to paddle with a larger paddle, as the paddle blade is equally locked in place. the only difference should be the slight increase in lifted water at the exit.

The only explanation I see is that the paddle is never locked, but the larger the paddle provides more locking factor and you need more power to drag the boat past the paddle - because of the increased lock

Thus, the whirlpools comes from moving the water behind the paddle and slippage of the paddle.

Btw, it is a myth that airplane wings get most lift from the Bernoulli's principle. the downwind pressure of air from the underside of the wing is also an important lifting factor (ref the pressure holding your hand out the window). If in doubt, have a look at the symmetrical wings of an aerobatic airplane :-)
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7 years 6 months ago #20016 by Kocho
I wonder, does anyone have the speed at which the paddle slices out through the water in say sprint kayaking vs. long distance kayak/ski race? If we have this speed measured (I'm sure some article somewhere online has that number) we can see if the paddle is moving more in the "planing" speed or more in a "displacement" mode.

I think you are right that for as long as the paddle is not primarily plaining, it will possible and it is happening that the paddle is indeed slipping back. There, the larger blades are harder to overpower, so stronger paddlers can take advantage of this and transfer more power to forward motion instead of stirring whirlpools...

My small wing definitely feels less powerful and does not resist as much as my mid-wing during a powerful forward stroke and in bracing. When I increase my cadence, I can feel more of that "wing" stroke feel coming together with either paddle - I think they move longer in the planing mode when the paddle's speed through the water is higher...

I also paddle a Greenland paddle with my sea kayaks. It has a symmetrical foil shape blades near the tips. One of my new own designs has a half foil (flat on the one side, foil on the other)With these paddles it is very easy to notice the transition between planing mode where there is virtually no slippage and drag/displacement mode where they rely on slippage. Dona sculling motion and gradually increase the angle of attack until the paddle "stalls" - the lift force you feel disappears and the paddle becomes harder to move and makes whirlpools (wasting your power for almost no use). In contrast, at low angles of attack, the paddle wants to pull away from you - it clearly does not slip back towards you but instead planes strongly and away from you. Kayak wing paddles have a bit less of this clear wing effect - they are designed to offer stronger drag forces than a Greenland paddle is - use the Greenland paddle without a cant/wrong angle of attack, and it flutters and loses power easy, so it is a good aid in letting you know when your technique is lacking.

fredrik wrote: According to the "books" the wing paddle is supposed to be locked in the water and the boat moves forward relative to the locked paddle.

I have difficulty believing that this is the absolute picture. If the paddle is locked with a - say - medium paddle (no slippage in the water, just the outward movement) then it should not be any more hard to paddle with a larger paddle, as the paddle blade is equally locked in place. the only difference should be the slight increase in lifted water at the exit.

The only explanation I see is that the paddle is never locked, but the larger the paddle provides more locking factor and you need more power to drag the boat past the paddle - because of the increased lock

Thus, the whirlpools comes from moving the water behind the paddle and slippage of the paddle.

Btw, it is a myth that airplane wings get most lift from the Bernoulli's principle. the downwind pressure of air from the underside of the wing is also an important lifting factor (ref the pressure holding your hand out the window). If in doubt, have a look at the symmetrical wings of an aerobatic airplane :-)

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7 years 6 months ago #20023 by Ric
Kocho, I think you have tweaked something that's talking to me. Plus you prompted me to do some reading on these Greenland paddles - quite interesting for sure!

What is this "planing" vs "displacement" mode?

You talk about changing the angle of attack, which I think might be key to me at the moment. What angle are you talking about?

i.e.
- when viewed from the side, do you mean paddle is vertical vs quite flat?
- viewed from the front, paddle vertical or flat?
- viewed from the top, paddle blade is perpendicular or parallel to the boats movement?

or some other angle I haven't listed.


I must say this distance touring looks like a lot of fun having read some of the Greenland blogs.

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7 years 6 months ago #20024 by Kocho
By angle of attack I mean what the term means for airplane wings. Google it. Imagine a plane flying horizontally (not ascending or descending), looking at it from the side: the wing cross section appears to be pointing a bit upwards. Something like this

===/====>

(but of course with less upward direction) assuming the plane is flying from left to right. If the wing was flat like this

===--====>

the angle would be 0. If the wing was perpendicular like this

===|====>

the angle would be 90. If the wing is pointing down,

===\====>

the angle would be negative and the plane would be descending rapidly and forcefully. The angle between the wing and the direction of flight is the angle of attack. The angle of attack should be relatively small to minimize turbulence and allow the plane to fly. If the pilot tries to tilt the nose of plane up too much while it is still moving forward, the plane will not go up faster, instead, it will "stall", lose its lift, and fall down. Same if you fly it too slow.

Planes generally try to keep that angle positive and small and move fast enough so that the air moves fast around the wing and creates enough lift to keep them flying ;)

Similarly for your rudder. When you go straight, the angle is 0. If you tilt it a bit to the side, it generated lift/pressure and the boat turns. If you tilt it too much sideways, it "stalls", meaning it begins to drag and create turbulence and becomes ineffective at turning the boat.

For a kayak paddle, say you have it in the normal catch position, power face facing directly to the rear. A 90 degree angle of attack would be if you are dragging the paddle back and parallel to the boat, keeping the blade at a 90 degree to the boat if seen from above, and not slicing out at all. That's how canoe paddles move next to the canoe. 0 degrees would be if you are slicing it out to the side perpendicular to the boat while still keeping the power face facing to the rear (which obviously will not move you anywhere, this is just for illustration).

In a normal wing stroke, you do keep the paddle about perpendicular to the boat as seen from above and you are dragging it back and slicing it out at the same time. This translates to an angle of attack of somewhere between 0 and 90 degree, closer to 90 than to 0 with a wing paddle would be my guess. At such angles I think there is some "lift" generated, but the paddle relies also on a lot of drag too to propel you forward.

With an airplane wing, the angle of attack is much smaller, much closer to 0 than to 90 degree. With a Greenland paddle too, if used with a canted stroke, the angle of attack is small, so the paddle generates plenty of lift in addition to using some drag to propel you. With a Greenland paddle you generate lift in one of two ways, depending on your paddling technique of choice - unlike a wing paddle, with the Greenland paddle you can be slicing downward/inward during the catch and the power phase of the stroke and then slicing upwards/outwards towards the end of the stroke before the exit; or you can use it exactly as you would use a wing paddle: slicing out through the entire stroke after the catch.

What I was describing in my previous post was if you are doing a sculling motions that you normally do to drag the boat sideways. That's when you rely only on the generated lift to move the boat sideways - you are not drawing the paddle closer to the boat, it stays at the same from the boat and you are sliding it fore and aft with the power face towards you and at a bit of an angle to allow the lift to happen. If during that sculling motion you angle the paddle too much you will feel the lift go away.

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7 years 6 months ago - 7 years 6 months ago #20036 by Gazz
You can get a feel for what's happening by drawing your paddle through the water whilst standing at the edge of a swimming pool. With an angle of attack square to the direction of travel the blade will create maximum vortices from both outer edges as there is maximum drag and is therefore, I'm guessing, fully stalled so far as generating lift. A slight feather and the resistance decreases, the blade stabilizes and the lift effect is felt accompanied by trailing edge vortex. I was reading about Bernouli and hydrodynamics etc but for me I also need a practical exercise such as the pool to help my understanding.
What surprises me is how much angle away from square you can go to and still generate significant resistance and lift. However I suspect that the further away from a square angle the faster you will need to draw the paddle through the water to maintain lift. Somewhere in there is an angle and rate that suits the individual paddler for maximum efficiency. Or, is there an absolute singular angle and rate the the paddler must strive for through technique. The "whirlpools", it seems to me, are simply a product, to varying degrees, of the movement of the wing shape through water as no matter how much I vary the angle I always generate vortices. ( Apart from a virtually fully in line and therefore useless angle ). This is standing on the pool edge of course and not in the ski where resistance is transferred into forward motion so the paddle doesn't travel as far through the water but even if I simulate the ski's travel by walking forwards along the pool edge whilst simulating paddling I still generate a vortex. So don't worry about the vortices and focus on technique.

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