Dragging

Dragging

Post by Alexander K » Wed, 30 Nov 1994 07:51:26


Ok, here is a question that has been puzzling me a few friend for a while.
If you are swimming (reasonably fast) and someone is swimming behind you
inside the wake, do you

a) Go faster or slower?
b) Use more or less energy  to maintain the same speed?

Some argue that since the person is swimming behind you is moving water, that
water will push you forward.  Others believe that since you are pulling water
back that the person behind you is creating a negative pressure zone and
thus causing drag.  

All comments welcome.

Alex.

 
 
 

Dragging

Post by arthur christopher » Wed, 30 Nov 1994 10:38:07


Quote:
>Ok, here is a question that has been puzzling me a few friend for a while.
>If you are swimming (reasonably fast) and someone is swimming behind you
>inside the wake, do you
>a) Go faster or slower?
>b) Use more or less energy  to maintain the same speed?
>Some argue that since the person is swimming behind you is moving water, that
>water will push you forward.  Others believe that since you are pulling water
>back that the person behind you is creating a negative pressure zone and
>thus causing drag.  
>All comments welcome.

I don't really know what a negative pressure zone is, but I think that the
prior would be the case...=)

Chris
--
******************************************************************************
* Never give up on what you really want to do.  The person with the big      *
* dreams is more powerful than one with all the facts.                       *
******************************************************************************

 
 
 

Dragging

Post by James Tapp » Wed, 30 Nov 1994 18:55:36

: Ok, here is a question that has been puzzling me a few friend for a while.
: If you are swimming (reasonably fast) and someone is swimming behind you
: inside the wake, do you

: a) Go faster or slower?
: b) Use more or less energy  to maintain the same speed?

: Some argue that since the person is swimming behind you is moving water, that
: water will push you forward.  Others believe that since you are pulling water
: back that the person behind you is creating a negative pressure zone and
: thus causing drag.  

: All comments welcome.

: Alex.

The guy in front benefits from those behind, but not a much as those
behind benefit from the guy in front. Hence cyclists' rotating pace lines.

--
+------------------------+------------------------------------+---------+
| James Tappin,          | School of Physics & Space Research |  O__    |

|       "If all else fails--read the instructions!"           |         |
+-------------------------------------------------------------+---------+

 
 
 

Dragging

Post by Melba Kurm » Wed, 30 Nov 1994 19:27:24

Quote:


>Subject: Dragging
>Date: Mon, 28 Nov 1994 22:51:26 GMT
>Ok, here is a question that has been puzzling me a few friend for a while.
>If you are swimming (reasonably fast) and someone is swimming behind you
>inside the wake, do you
>a) Go faster or slower?
>b) Use more or less energy  to maintain the same speed?

Throughout my years of swimming competitively, dragging was always a fairly
major workout issue.  We were absolutely convinced that it's easier to swim
right behind someone.  In fact, swimmers would get angry if someone was
dragging off of them too much, or would help a tired friend through a tough
workout by letting them drag.

I'm not sure if there's a real physical reason (i.e. water currents) that
makes dragging easier than swimming in front, or it it's psychological (i.e.
havingthe person if front pace you and count laps).

Having someone drag off of you makes it harder to swim.  But again, I'm not
sure if this is physical or psychological.   Whatever the reasons, the dragger
uses far more energy than the draggee.

Melba Kurman

 
 
 

Dragging

Post by Richard Osterbe » Wed, 30 Nov 1994 23:26:32

: The guy in front benefits from those behind, but not a much as those
: behind benefit from the guy in front. Hence cyclists' rotating pace lines.

Um... *no*.  Have you ever been dragged on from directly behind?  The
water flow gets all screwed up... causing turbulance... which slows you
down.  You can *feel* them dragging on you.  It would also seem to be
rather impossible, by the laws of physics, for both to benefit from
something like that... though that may be wrong (the water friction is a
non-conservative force).  If both people benefit... what would happen if
you had say 10 people in a lane... swimming so that everyone was dragging
off the person in front of them?  Would the speed of the swimmers
constantly increase?

-Rick

--
+--------------------------------------------------------------------------+

+--------------------------------------------------------------------------+

 
 
 

Dragging

Post by Jean Freema » Thu, 01 Dec 1994 01:27:12

On Mon, 28 Nov 1994 22:51:26 GMT,

Quote:
>Ok, here is a question that has been puzzling me a few friend for a while.
>If you are swimming (reasonably fast) and someone is swimming behind you
>inside the wake, do you

>a) Go faster or slower?
>b) Use more or less energy  to maintain the same speed?

>Some argue that since the person is swimming behind you is moving water, that
>water will push you forward.  Others believe that since you are pulling water
>back that the person behind you is creating a negative pressure zone and
>thus causing drag.  

>All comments welcome.

>Alex.

the person who goes behind will have it easier and therefore should go
faster. As coaches we have made lanes change leaders just for this reason.

     MMMMM MMMMM     Jean Freeman                  221 Cooke Hall
      MMM   MMM      University of Minnesota       1900 University Ave. SE
     MM MM MM MM     Head Swimming Coach           Minneapolis, MN 55455
    MM   MMM   MM    Women's Swimming and Diving
   MM   MMMMM   MM          

 
 
 

Dragging

Post by Stephen O. Nels » Thu, 01 Dec 1994 09:47:27

Quote:

>Um... *no*.  Have you ever been dragged on from directly behind?  The
>water flow gets all screwed up... causing turbulance... which slows you
>down.  You can *feel* them dragging on you.  It would also seem to be
>rather impossible, by the laws of physics, for both to benefit from
>something like that... though that may be wrong (the water friction is a
>non-conservative force).  

        Actually, two people dragging through the water like that would
create a net conservation of energy.  The problem for the first swimmer is
that they have to go faster to keep ahead of the guy behind them (who gets
the lion's share of the efficiency effect), and the normal turbulence at
their feet may be disturbed.  If the person behind was actually dragging the
front swimmer back they would have to be going slower than the front
swimmer, and they would quickly fall behind (water doesn't make a very good
rope).  Worked it all out with a mechanics professor.  Should be valid.

Quote:
>If both people benefit... what would happen if
>you had say 10 people in a lane... swimming so that everyone was dragging
>off the person in front of them?  Would the speed of the swimmers
>constantly increase?

        Asked about this, too.  If you think about it, then there's going to
be a certain set pace for the lane from the first person on back, and while
the speed of the swimmers will increase to a certain extent, after the first
couple the effect will just approach a limit (which will depend on the
atheletic ability of the people in the lane) that won't be much faster than
the speed of the lane with one or two drafters (and a leader).

Steve-O  (hope that was illuminating)
--
begin 644 hasig.gif
M1TE&.#=A"0`%`(```````/___RP`````"0`%```"#$1\<<8)S]YRTEE0```[
`
end

 
 
 

Dragging

Post by Tro » Thu, 01 Dec 1994 13:06:13

My humble opinion about the dragging issue, from one who definitely
benefits from it...
The person behind gets a huge benefit...last week, did a set of 8x100
on 1:10 and could barely make it (not a good day for me)
Next day, we had a set of 20x100 on 1:05, and I made 14 before
eventually failing.  Without the aid of drafting, I could have made
maybe 5
As for the person in front, does drafting hurt them or help them?
Swimming creates a LOT of trubulence.  This turbulence is what pulls
the second person along.  The turbulence will be there whether or not
there is someone there to take advantage of it.  No psychologically,
it can be harmful to know that someone is sucking on your wake, but I
believe the water flow is so screwed already that the to speak of
added turbulence is sort of pointless.  If you find that it is harmful
to know that someone is sucking off your wake, then just really work
the 10 yards before and after a turn.  You should be able to stretch
enough of a lead before they can match the move that they wont be able
to suck themselves in.
Troj
 
 
 

Dragging

Post by JOERGEN KARLS » Fri, 02 Dec 1994 00:15:50

The best way to swim faster, is to swim beside one who swim a bit faster
than yourself. You can take advantage of the wave the swimmer beside you
makes, but if you "fall off" the wave, you lose your speed. I've done this
dozen of times, it works. Try it, actually it's really fun. If you're lucky
you can swim much faster, than you usually do. A few years ago I helped a
friend to qualify to the norwegian championship by doing this. He swam 2/10
sec. faster than he usually did on 50 m crawl. That's what a call dragging!

Joergen

 
 
 

Dragging

Post by James G. Ack » Thu, 01 Dec 1994 23:21:16

        IMO, the worst part of leading a lane is hitting all the water
flow coming straight at you right after you turn, _plus_ turbulence.  
Once I'm past the trailing swimmers, things get much better.  This
obviously doesn't apply to long-distance open water swimming, but
you sure can feel it in the pool.

===============================================
|  James G. Acker                             |

===============================================
All comments are the personal opinion of the writer
and do not constitute policy and/or opinion of government
or corporate entities.

 
 
 

Dragging

Post by Jean Freema » Fri, 02 Dec 1994 01:10:33

On 29 Nov 1994 09:55:36 GMT,

Quote:

>: Ok, here is a question that has been puzzling me a few friend for a while.
>: If you are swimming (reasonably fast) and someone is swimming behind you
>: inside the wake, do you

>: a) Go faster or slower?
>: b) Use more or less energy  to maintain the same speed?

>: Some argue that since the person is swimming behind you is moving water, that
>: water will push you forward.  Others believe that since you are pulling water
>: back that the person behind you is creating a negative pressure zone and
>: thus causing drag.  

>: All comments welcome.

>: Alex.

>The guy in front benefits from those behind, but not a much as those
>behind benefit from the guy in front. Hence cyclists' rotating pace lines.

>--
>+------------------------+------------------------------------+---------+
>| James Tappin,          | School of Physics & Space Research |  O__    |

>|       "If all else fails--read the instructions!"           |         |
>+-------------------------------------------------------------+---------+

I believe the lead swimmer also benefits from cirlce swimming. The more in
the lane the more benefits ( that is easier to swim). I think the water in
that lane begins its own circle suction. So the lead swimmer does not
really drag that second person with them. This is based on years of
obsrvation rather than personal experience.

     MMMMM MMMMM     Jean Freeman                  221 Cooke Hall
      MMM   MMM      University of Minnesota       1900 University Ave. SE
     MM MM MM MM     Head Swimming Coach           Minneapolis, MN 55455
    MM   MMM   MM    Women's Swimming and Diving
   MM   MMMMM   MM          

 
 
 

Dragging

Post by Timothy B. Madd » Fri, 02 Dec 1994 02:16:10

This subject seems to come up every few months or so.  Maybe we should
get somebody to put a definitive answer in the FAQ.



Quote:
>: The guy in front benefits from those behind, but not a much as those
>: behind benefit from the guy in front. Hence cyclists' rotating pace lines.

>Um... *no*.  Have you ever been dragged on from directly behind?  The
>water flow gets all screwed up... causing turbulance... which slows you
>down.  You can *feel* them dragging on you.

Fluid drag is typically divided (for steady flows) into two components:
form drag and friction drag.  The former is more likely the component
that provides assistance to the leader of the pack.

As you move through still water, the water directly in contact with your
skin is forced to move with you.  This results in entrainment of the fluid
due to skin friction as you move along.  As the second person moves along
behind you in this entrained wake, they will experience less skin friction.

Additionally, your body also experiences a form drag due to its shape,
involving pressure differentials between the front and rear.  For an ideal
fluid (inviscid) moving about the body, the fluid will accelerate from a
point of stagnation at the front end of the body to a maximum at the sides,
then decelerate as it moves to the rear of the body.  In a viscous flow,
the fluid's velocity near the body is decreased, so that as it comes to
the rear of the body and begins to decelerate, it eventually reaches a
point where its inertia can no longer overcome the pressure gradient, and
the flow reverses direction.  This phenomenon is called separation, and
results in a low pressure 'wake' forming behind the body.  The resultant
high pressure at the front and low pressure at the back produce a form
drag due to the pressure difference.

So, as a swimmer moves in behind you, they gain the benefit of the increased
velocity of the entrained fluid due to your skin friction.  You derive
a minimal benefit from the resulting increase in pressure caused by the
acceleration of the fluid around their front end, reducing your form
drag (note that your low-pressure wake will also reduce theirs).  The
result is less force required to maintain a speed for the pair of swimmers.

Note that it's pretty difficult to pull away from somebody who is drafting
along behind you.  This is probably what you *feel* ... you increase your
effort and it doesn't seem to help you get away.

Quote:
>...It would also seem to be rather impossible, by the laws of physics,
> for both to benefit from something like that...

This is a fairly commonly held myth.

There are other considerations to this question as well... the effect
of bubbles in the flow which decreases the surrounding fluid density,
the effect of vortex and eddy shedding from the leader (resulting in
a bit of buffeting, esp. off of a ***stroke kick), and wave drag.
Wave drag can be important when swimming next to another swimmer,
especially in a sprint.

Quote:
>...what would happen if you had say 10 people in a lane...
>Would the speed of the swimmers constantly increase?

No, instead the equilibrium speed of the swimmers would eventually reach
a maximum that is higher than the speed the group would attain by swimming
far apart (the speed of their collective mass center).  Good examples of
the useful nature of drafting abound in bicycling.

Quote:
>+--------------------------------------------------------------------------+

>+--------------------------------------------------------------------------+

--
- tim


 
 
 

Dragging

Post by Timothy B. Madd » Fri, 02 Dec 1994 02:18:38

Good point Troj, on using those turns.  I find my turns and breakouts to
be fairly quick compared to the other swimmers that swim at my pace in
workouts, so I can usually 'get away' from a drafter using the walls.

It works even better in reverse... a good hard push-off, tight streamline,
and good first two strokes can get you into a good draft pretty easily.
Of course, I never do that, I work HARD in my workouts (right).

--
- tim


 
 
 

Dragging

Post by Alexander K » Fri, 02 Dec 1994 01:26:58


Quote:

>: The guy in front benefits from those behind, but not a much as those
>: behind benefit from the guy in front. Hence cyclists' rotating pace lines.

>Um... *no*.  Have you ever been dragged on from directly behind?  The
>water flow gets all screwed up... causing turbulance... which slows you
>down.  You can *feel* them dragging on you.  It would also seem to be
>rather impossible, by the laws of physics, for both to benefit from
>something like that... though that may be wrong (the water friction is a
>non-conservative force).  

I agree with Richard.  When you are swimming you can feel someone dragging off
you.  I think the main difference between cycling and swimming is that in
cycling you are pushing the air ahead of you thus creating a bow wave.  This
effect would benefit both people (the one in front and the one behind). The
person in front is pushed by the bow wave created by the rider behind and the
rider behind rides in a slip stream.

On the other hand, in swimming you pull water behind you to move forward.
This presents a totally different case.

Alex.

 
 
 

Dragging

Post by Terry Laughli » Fri, 02 Dec 1994 22:09:45

Very interesting discussion on dragging. I'm a Master swimmer,
also a coach for 22 years, so I've seen and experienced it from
both sides. From the coach's perspective: I often employed the
advantage of drafting to benefit lesser swimmers and help them
complete workout sets they could never have achieved on their own
without drafting. I would set up the lanes so there was a fast
swimmer at the front of each, then a slightly slower one behind,
and so on so the slowest swimmers in the group were arrayed
across the rear of the lanes I had set up. Then I would give a set
which was challenging but not impossible for the faster swimmers,
but normally a huge reach for those at the end. It was always
quite clear that the further back in the loop you were, the more
of a "current" effect you benefited from. I could get some awesome
"team" performances on difficult sets. It would be a big
confidence booster for the developing swimmers and the team effort
to have every member successfully complete the set would build
team rapport.
From a swimmer's perspective: I swim alone most of the time so I
don't deal with drag or draft, but when I get into a group and
swim in circles: When I'm drafting, I routinely swim 5-10% faster
for the same effort than when alone. Some of this is draft and
some from the psychological benefit of getting to "compete--race
and chase others" in workout. If I lead the lane, I feel I have to
work a bit harder, not because those behind drag me back, but
because I have to fight thru their turbulence.