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  #11  
Old 07-23-2016
keithbowden
 
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ZT

What would your interpretation be of "deep arm" and drag in this context versus a "shallow arm" i.e flatter arm and closer to surface?
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  #12  
Old 07-23-2016
Zenturtle Zenturtle is offline
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I dont know. She spears a bit up instead of down. Not ideal, certainly not for normal adult swimmers.
These are questions that can be answered very easy on that running water pool with a force sensor.
One hand on the force sensor. other arm at different spear depths. Try differnt leg positions, arm shapes in the water, kicking patterns, comparing a big crossfit guy against a 11 year old girl etc etc
Half an hour is enough to clear a lot of all the lingering swim questions.

Its surprising how low the drag on a simple horizontal body is.
48N at 1.5 m/sec which is the same as 1min 6sec/100m pace.
1m/sec is the same as 1.40 min/100m pace, or 25 min/1500 m. This pace requires only 21Newton, which is only 2KG for a simple streamlined body!
If you dont kick and keep the body horizontal, only the extra drag of the pulling arm comes on top of that drag, so it should be a piece of cake to swim that pace in theory.

Actively lifting half of your head out of the water is already 4 kg extra, so that would cost as much as swimming 1.40/100m pace on itself.
Weird weird weird.

Last edited by Zenturtle : 07-23-2016 at 03:28 PM.
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  #13  
Old 07-23-2016
keithbowden
 
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I get the impression that the force on the arm might be higher initially (after entering water), but is continuously decreasing over the period of time it takes for the arm to eventually recover again. This caused by the arm in continuous motion and the main part of the body travelling forward - a kind of cancelling effect o the force?

A sensor suit on a swimmer would be interesting with the data fed back to a computing system to crunch all the various parameters to provide a visualisation of what is actually happening...
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  #14  
Old 07-23-2016
Zenturtle Zenturtle is offline
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If you dig into it, swimming is incredibly complex.
http://icb.oxfordjournals.org/content/42/5/1018.full
We are only able to scratch the surface at the moment.
I dont want to go there and like to keep it as simple as possible, relating everything to personal perception, and straightforward simple hydromecanical examples.

Last edited by Zenturtle : 07-23-2016 at 07:35 PM.
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  #15  
Old 07-31-2016
sclim sclim is offline
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Quote:
Originally Posted by Zenturtle View Post
How much drag does a deep knee produce?
Look at the 5min 30 mark to see the drag difference between a straigh body and a body with downward angled upper legs.
https://www.youtube.com/watch?v=xa-4jgjS6sY
An extreme example, but usable as a rough guide.
2 very deep knees, drag goes from 48 to 81 Newton, a 68% increease.
In more realistic, less extreme cases I guess a 20 -30% drag increase is still possible.
Rather remove that drag source than give 20-30% higher force to hold the same speed without that upperleg/kneebend disturbing horizontal line.
For some swimmers its better to not kick at all from a drag perspective.
ZT: how in the world did you uncover that nugget??? I waited through 5:30 not understanding most (but sort of interpreting "free-style" "dolphin kick" etc by the Japanese transliteration of the English terms, and some recognition of common Japanese and Chinese script characters. But I never would have been able to search this out.

That horizontal force transducer in the endless pool plume is a neat trick. I sometimes wonder when I'm swimming if I would be presenting less cross sectional surface area by angling my shoulder girdle more when I'm spearing my lead hand, for example; but this is all idle speculation, as my sensitivity to velocity changes is not good enough to get reliable feedback. I would imagine that constant exposure to that fine information feedback would be excellent for improving the subtle details of your streamlining
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  #16  
Old 08-01-2016
Zenturtle Zenturtle is offline
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full throttle with propulsive fins and start doing with your front end what you are ususally doing can give some enlighting moments...

I have been towed by my fathers boat often during summer holidays and that gives the same impression.
Its amazing how little speed it takes to lift the body substantially out the water.
Watched Rynomy Kromowidjojo sprint on the news and her upperbody was like a half submerged surfboard. Impossible to sustain offcourse but for max effort sprint there certainly is some lifting.

did you see how well most of those little kids swim?

Last edited by Zenturtle : 08-01-2016 at 06:16 AM.
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  #17  
Old 08-01-2016
Grant Grant is offline
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Up until about five years ago I could feel my body lift or plane higher in the water when I initiated my sprint to the finish on a 50 or 100m race. It would hold for about 5m. Not any more though. The speed just isn't there to achieve that result.
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  #18  
Old 08-02-2016
Zenturtle Zenturtle is offline
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Some good Polish kicking eye candy. Too much kicking for us, but some good footage of basic kick technique.
Scary overstretched knees in the kick of the guy.
https://www.youtube.com/watch?v=IRTKf0b1e-w

Last edited by Zenturtle : 08-02-2016 at 10:48 PM.
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  #19  
Old 08-14-2016
Zenturtle Zenturtle is offline
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And another good TI example thats a pleasure to watch.
Still some 6BK in place, but nice smoothness and very stable bodyline.
https://www.youtube.com/watch?v=wAAFvdc1deY
He has exactly the right downkick -pull-spear connection/technique in my view.
The first stroke often shows the basic swim mechanism in the swimmer. Watch how he powers his whole stroke from his first rightleg downkick-spear-pull after it is first set up.Thats the right internal clock connection.
If you compare this action with the kneekicking upperleg timing you see how the kneekicking disturbs the possibility to get one seamless powerfull connection to the water and the next stroke delivering continuous propulsive power waves through the body.

his stable straight tracking ability is the best I have seen in a long time. Free arms on a very stable main vessel.
https://www.youtube.com/watch?v=QlQujjXLPHw

Last edited by Zenturtle : 08-14-2016 at 10:41 AM.
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