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  #1  
Old 12-15-2012
craig.arnold@gmail.com craig.arnold@gmail.com is offline
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Default Ground Effect?

So here's something weird.

I swim better in shallow water. Or at least I think I do. The pool today was 1.2m.

In that depth I was getting 11-12 SPL. In a deeper 1.2 -> 1.8m pool on Thursday I was getting 14-15SPL. The last time I was getting 12 SPL was 8 weeks ago on the workshop.

I feel like I'm going faster too. And the shallow end always feels easier and faster than the deep end in pools with a gradient.

I can think of 3 possible explanations:

1. Physics: There is in fact a hydrodynamic equivalent of the ground effect and pushing against water which has ground pushing back against it provides some benefit.

2. Perceptual: The change in my SPL is simply that I was swimming well today and has nothing to do with the depth, but swimming in a shallow pool FEELS faster because the ground is close and there is a perceptual difference because the ground is rushing by close to your eyes.

3. Psychological: On a subconscious level I am afraid of deeper water, even if it's not very deep. This psychological effect affects the way I swim and feeling safer makes me swim better.

Of course lacking easy access to a parallel universe I cannot split myself into two and run a control.

What do you think?
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  #2  
Old 12-15-2012
CharlesCouturier CharlesCouturier is offline
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Strange case, other than element number 2 and 3, I don't see what the problem could be.

Obviously, if we're talking 2 different pools, then it may simply be that one pool is just faster than the other. Based on your input, it would be significantly faster.

Last edited by CharlesCouturier : 12-15-2012 at 07:54 PM.
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Old 12-15-2012
tonyP tonyP is offline
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Ground effect is a real fact of aerodynamics.

It comes into play at takeoff and landing, occurring within about 1 wingspan of the ground - i.e. about 11 meters for a Cessna, and about 65 meters for the bird I fly - the Boeing 777.

As I recall from aerodynamics classes ( loooong ago....) the cause is a reduction in 'induced drag', having to do with the interruption of spanwise airflow around the wing tips (also the reason many newer planes are sporting wing tips that curve upward).

I'll leave it to more knowledgeable swimmers / hydrodynamicists to equate the above to swimming, cheers.
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Old 12-15-2012
CharlesCouturier CharlesCouturier is offline
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In swimming, it's reversed.

A fast pool is a deep pool.
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  #5  
Old 12-16-2012
Richardsk Richardsk is offline
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I may be wrong but I think that close to the bottom of a pool interference effects would outweigh any ground effect. I understand that there is an optimum depth for body dolphins (or breaststroke pull-downs). I seem to remember a depth of about 0.8 of a meter. I'm sure the information is out there somewhere. There's a video on youtube comparing Phelps and Chris Thompson doing underwater dolphins and Phelps is much deeper. The commentary is by Bob Bowman.
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Old 12-16-2012
CoachSuzanne CoachSuzanne is offline
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deep pools are faster everything else being equal. Maybe you are just swimming better?

Misty Hyman learned to do her body dolphin sideways facing a wall rather than facing the top or bottom of the pool because the vortex circles she creates don't get interference from the surface that way and she goes faster.

I can't even create vortex circles with a body dolphin...more like vortex squares. Or lumps of coal.
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  #7  
Old 12-16-2012
craig.arnold@gmail.com craig.arnold@gmail.com is offline
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Thanks for the comments.

Clearly then I just found a bit of lost mojo yesterday and the shallow pool thing is just a coincidence.
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  #8  
Old 12-16-2012
WFEGb WFEGb is offline
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Hi Craig,

Quote:
Originally Posted by craig.arnold@gmail.com View Post
... I swim better in shallow water. Or at least I think I do. The pool today was 1.2m.

In that depth I was getting 11-12 SPL. In a deeper 1.2 -> 1.8m pool on Thursday I was getting 14-15SPL.......

3. Psychological: On a subconscious level I am afraid of deeper water, even if it's not very deep. This psychological effect affects the way I swim and feeling safer makes me swim better. ...
Don't miss the visual effect; in shallow water your angle velocity when fixing a point at the bottom is much larger than in deeper water. (And we have to do it altime. Otherwise we can not see anything.) Although that will not explain the additonal 2-4 strokes.

Regards,
Werner
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Old 12-16-2012
craig.arnold@gmail.com craig.arnold@gmail.com is offline
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Erm yes.

I clearly overstated; I didn't drop 2 strokes for the whole session, just for the 10 lengths I was counting and trying to lengthen my stroke.
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  #10  
Old 12-17-2012
sinker sinker is offline
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[QUOTE

2. Perceptual: The change in my SPL is simply that I was swimming well today and has nothing to do with the depth, but swimming in a shallow pool FEELS faster because the ground is close and there is a perceptual difference because the ground is rushing by close to your eyes. [/quote]

No. 2 is something I constantly have to concentrate on or it will affect my stroke rate and balance. My pool is two thirds shallow and one third deep. In the shallow end the tiles below me are moving at a good clip, but when entering the deep end the perception is that I have dramatically slowed because the deeper tiles seem to be moving so much more slowly. I have a natural tendency to pull harder and speed up, but this increases slippage and throws my balance off. Some days are better than others but it always requires focus to overcome this tendency.
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