Row, row, row your bots: But are they synchronized?

June 9, 2017
Credit: CC0 Public Domain

To get maximum propulsion, should a boat's team of rowers set their strokes to the same rhythm? Or should the rowers stagger the dropping and pulling of the oars through the water? Athletes and scientists have looked at the question, offering illuminating but inconclusive observations. But this month's Physics Today features a special article by fluid mechanic researchers at the Paris École Polytechnique laboratory of hydrodynamics (LadHyX), who provide data and fundamental physics approaches for coaches, sportspersons and scientists to keep in mind the next time they observe or get into a crew boat.

For their study, conducted in the pool of the École Polytechnique, the LadHyX researchers built a 2-m-long with eight robotic rowers and controlled the speed and phasing of the strokes; Physics Today has posted two of their runs online.

In "Row bots," Jean-Philippe Boucher, Romain Labbé and Christophe Clanet first offer some of the fascinating sports and scientific background for their experimentation. In the early 1980s, Soviet women's teams that participated in the World Rowing Championship placed the coxswain (the steerer) in the middle of rowing pairs, to facilitate out-of-phase strokes. (On race days, they played it safe and rowed in sync.)

Scientists, too, have been intrigued in various ways. In a 2010 study of shrimp krill movement, a Georgia Tech team found that this migratory marine denizen maximized its per exertion velocity by staggering the rhythmical flexing of its five pairs of legs.

History aside, these researchers wanted to come up with a clear sense of whether rowing in sync, or not, is better for speed. Their experimental boat is one-tenth the scale of a competitive race boat with a realistically shaped fiberglass hull. They compared the synchronous rowing run with trials in which they varied the stroke speed and phase relation of the eight robotic rowers. In addition to measuring the overall , the LadHyX researchers determined velocity fluctuations.

Read "Row bots" for free in this month's Physics Today to find out what the LadHyX found about synchronous and krill-like desynchronized rowing for raceboat competitions.

Explore further: Back pain the norm for young Perth rowers

More information: Jean-Philippe Boucher et al. Row bots, Physics Today (2017). DOI: 10.1063/PT.3.3606

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winthrom
5 / 5 (1) Jun 09, 2017
Nice non-article. "Please click the link" is not an article.
Urgelt
not rated yet Jun 09, 2017
Eh, yeah, well. At least the link is free to read.

And it brings up an interesting question. The authors concluded that synchronous rowing is a bit faster than asynchronous rowing, then attributed that to the synchronous surge of the hull resulting from the synchronized backstroke, where the rowers' bodies are moving rearward, propelling the hull forward.

That makes no sense. The movement of masses back and forth is identical whether the rowing is synchronized or asynchronized. You would expect a higher peak velocity from the synchronized backstroke, but the gain would be lost on the power stroke as the rowers all move their bodies forward. It should be a wash, just from a mass movement standpoint.

I'm wondering if the authors missed something. Peak velocity is higher with synchrony, so the hull may be doing something different to temporarily reduce friction.
nkalanaga
not rated yet Jun 10, 2017
I suspect that the primary advantage of synchronized rowing is that one can put more rowers in a boat with getting the oars tangled. More "horsepower" equals more speed, which is an advantage for commercial or military craft. For a racing team, with a fixed number of rowers, the advantage would be much less.

Urgelt: I tend to agree with you on the movement of masses. If that was the only reason for the synchronized method being better, putting a pendulum in the boat would make a good, cheap engine!

Winthrom: Agreed. Click Bait?
nkalanaga
not rated yet Jun 10, 2017
"with getting the oars tangled" ?????

Obviously I wasn't typing too well. That should be "WITHOUT getting the oars tangled" !
nkalanaga
5 / 5 (1) Jun 10, 2017
OK, I've read the paper. The contribution from the rowers' position changes does make sense, but not intuitively. If the boat was free to move, yes, the rowers' back-and-forth motion wouldn't matter. But when the rowers move forwards, during the power stroke, the boat can't move backwards, because the oars are also pulling the hull forwards.

On the return stroke, the rowers move rearward, and the hull forwards, this time with nothing to prevent the motion. Thus, the center of gravity of the boat doesn't remain stationary as the two rowers and hull move relative to each other. There is a net forward acceleration. Weird, but it makes sense.

They note that for krill, swimming underwater with 10 legs, desynchronized is best, because the legs are underwater on both power and return strokes. Thus, changes in mass distribution have no effect.

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