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martyb writes:

An article in Physics Today delved into the question of which would be faster: rowing in phase with all of your teammates, or rowing out-of-phase:

Rowing is a challenging sport, and not just for athletes. It mixes physiology, mechanics, and fluid dynamics, so from a physicist's perspective, the sport is much more complex than the elegant movement of a rowing shell might suggest.

Many scientists have tried to work out the details of rowing propulsion, often with a view to improving the performance of rowing crews. For example, in a 1971 Science paper (volume 173, page 349), Thomas McMahon showed that the speed of a racing boat scales as the number of rowers to the power 1/9. In our research, we have taken a closer look at the boat speed within one rowing cycle. In a single stroke, a propulsive phase is followed by a gliding phase. As the figure shows, for racing boats, the variation in speed during the stroke is typically around 20% of the mean speed of 5 m/s or so. Such a variation is a consequence of the synchronized rowing of the crew, a technique that seems to be essential for success in top-level rowing competitions. Consider, however, that for a boat moving through water, larger fluctuations about the boat's average speed imply increased friction on the hull. As a consequence, the mean power dissipated due to fluid friction for speed variations typical of a racing boat is about 5% higher than it would be if the boat could somehow be propelled steadily at the same mean speed.

The investigators suspected that reducing the variation in speed would result in less friction and a higher average speed. To test this, they created a 'bot boat' where they could programmatically control the phase at which each mechanical rower placed their oars into the water — anywhere from 0 to 45° out of phase. Initial results showed that out-of-phase rowing was smoother. Yay! But the boat was slower! Why?

*SPOILER* (click to show) *SPOILER* (click to hide)

Supplement: The great row bot race

In rowing races, a crew's synchronized motion forcefully propels the rowing shell forward. But the jerky motion of the boat creates a lot of friction on the hull. Can the crew gain an advantage by rowing out of sync? The video shows two trials conducted at the École Polytechnique in Paris using a 1/10-scale boat and robot rowers. In the top panel each robot rows 45° out of phase with its neighbor. In the bottom panel the row bots simulate conventional synchronized rowing. The asynchronous rowing is smoother, but in this case, slow and steady loses the race.

Download Original Video (7.1 MB)

An old adage humorously suggested that "Scientists frequently find that a week in the library can save an hour in the lab." What experiments have you been involved in where the results were counter to your expectations?

Original Submission