Seems like we were discussing this just recently...
From active.comstory.cfmOpen ↗ &category=triathlon
Drafting gives serious swimmers an edge
By Jay Caldwell Anchorage Daily News
7/29/2003
Recently, a group from the University of Otago in New Zealand measured the effect of swim drafting
and reported its results in the July issue of Medicine & Science in Sports & Exercise.
Drag, or resistance through the water, is the principal mechanical factor impacting swim
performance.
The simplest way to think of this complex hydrodynamic problem is that it takes a lot of effort for
a swimmer to cut through clean water. A swimmer entering slightly disturbed water or water moving
forward a bit as a result of a previous swimmer's passage through it has an easier go.
In pools, this effect is lessened by the floating lane dividers.
The Otago group studied the ideal drafting position by observing swimmers in a flume. It comes down
to this: If you swim directly behind someone, though you're a bit less efficient, the ideal distance
is about 50 centimeters. (What with all the bubbles, visibility may be affected there.)
An almost identical effect can be obtained from 100 to 150 cm, almost 5 feet behind. So if you're
training in a pool, you'll only cheat yourself unless you stay back a full body length.
Drafting to the side, about a foot and half away, works quite well too. The New Zealanders were able
to define the ideal draft position as that which occurs when the trailing swimmer has his/her head
even with the lead swimmer's waist.
At this distance, the 6 percent to 7 percent decrease in drag can translate into a 2 percent to 3
percent performance gain, or up to 50 meters over a mile.
So there you have it. Athletes are always looking for -- and finding -- an edge. Be it equipment,
drugs, training, nutrition or strategy like drafting, there appears to be no end to the ingenuity of
the serious athlete. And "serious" has many definitions.
Jay Caldwell is director of the Alaska Sports Medicine Clinic.