Note relationship of swim direction to the river bank. The current was quite strong heading out, each time, though I did enjoy my dip in the water.
Following the 2014 Maryland Ironman swim, especially as I was in the early stages of the bike ride, I heard people commenting on their swim time, and how slow they were.
A little thought about the drag of one piece of fluid against another, and the drag created by the bank, explains why swim times were slower than many expected in the Choptank River. By about 20% for most people I talked to, including myself (Yes, I talk to myself). Fluid dynamics is fascinating, btw. Vector (arrow) length indicates local flow rate. Article linked to figure.
I had no idea what mine was at the time, but it is usually in the 1:15 to 1:20 region, with excursions towards 1:30. But this time it was 1:35, though it felt the same as usual. A quick look at the fluid mechanics of the swim course explained it. You swim against the current on the way out, but with very little help from this current on the way back. This is classic flow in a pipe, fluid mechanics, and it’s all part of the Ironman swim.
What I find interesting is the fact that the faster swimmers are affected much less than the slower ones, in terms of time. If I had time I’d use a mathematical model to explore this observation, but here is a ‘back of the envelope investigation.’ Intuitively, you might think that the slower swimmers spend more time being slowed down than the fast ones do. Maybe it’s a percentage thing? For instance, I was slowed from expected to actual time by 20%. My son, Nigel, who had his best race ever, 11th overall, would be expected to have a 55 min swim, but he attained a 1:05 in the Choptank, being to 18% slower, close to my level of delay.
This little book will change your perception of the world around you.
But whatever is, it is real, penalizing slower swimmers more than fast, strong ones. As a decent swimmer, but poor runner, I need all the help I can get (more about my run, later).
If you are interested in the effect of fluid flow on our lives as biological entities, I strongly recommend a delightful little book, ‘Life in Moving Fluids,‘ by Steven Vogel.
I spent many happy years studying fluid mechanics as a research pathologist, much of it computational. This experience introduced me to many remarkable features of leaves, bees, squid and the like, about which I had never really thought a great deal when it came to survival of the fittest on this challenging planet.
I took this study into my Ironman obsession, and I often think about flow vectors as I swim or ride my bike. On the run, I’m generally more concerned about my feet, which actually did amazingly well on this race, considering my recent running struggles.
Oh Yes! In Steve Vogel’s lab, during a visit years ago, I got to watch a Harris Hawk flying in a wind tunnel. It was one of those experiences that you never forget.
That’s it for now.
Happy Laps.
Important Note: These posts do not provide medical advice. You should always consult your physician before undertaking or significantly modifying an exercise program.
Copyright © 2010 Kevin T. Morgan aka FitOldDog, Old Dogs in Training, LLC.
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