"Mark P" <[email hidden]> wrote in message
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Quoted message said:At my workout this afternoon there was a woman in the lane next to me
who was attempting to break the one hour USMS distance record. She's in
the 40-44 age group where the current record is 5325 yds and she came in
at 5310 yds. Very fast, and so close to the record.
She was swimming in the end lane of the pool where the water is plenty
deep but the lane touches the wall. There's a deep gutter at the wall
but no rope or extra space between the lane and the wall. I'm wondering
whether this would add a little extra drag as compared to having another
lane on that side. Even 1% could have made a difference. Anyone know
the facts on this?
Yes.
There _is_ an extra drag from the wall being close.
Naval architects term this "bottom effect" - although it might in the case
you refer to be better described as "bank effect".
The column of water between a moving body and a fixed surface shears. When
the distance between the body and the surface is small, an extra drag can be
detected. This valuse of "small" depends mostly on three things:
a) the speed of motion of the body
b) the length of the body
c) the sensitivity of the measurement apparatus.
A fact that might surprise you is that the drag increases (proportionately)
as the speed of motion is reduced; this is due to the angle of shear being
more perpendicular and thus it will contact the surface before a larger
portion of the body has passed that point.
I've heard it said that for ships at common ship speeds (say 5 to 15 knots)
such an effect can be detected if the bottom is less than 200x the waterline
length of the ship.
No swimmer travels as fast as 5 knots, but the sensitivity of our
measurements are proportionately much less than those available when working
with an object as large as a ship. Countering this, the effect of the drag
is not linearly related to the separation (it is, obviously, greater when
this distance is smaller), and so with seperations of a metre or less, as in
your example, one might well expect there to be some detectable drag.
As far as I know there have not been any peer-reviewed studies on the effect
of the wall on swimming speed, but it is commonly thought to be a factor of
some small but not insignificant size.
Regulations for meets of international calibre state that the pool depth
must not be less than 2 metres; and that an extra empty lane be interposed
between the outside racing lanes and the walls (which in essence gives about
a 3 metre distance between a swimmer and the wall).
The difference between the record and her swim is less than three-tenths of
a percent.
Put her in lane 4 next time.
