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posted by cmn32480 on Monday June 12 2017, @04:03PM   Printer-friendly
from the row-row-row-your-bot dept.

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?

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

 
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  • (Score: 3, Interesting) by VLM on Monday June 12 2017, @06:38PM (2 children)

    by VLM (445) Subscriber Badge on Monday June 12 2017, @06:38PM (#524578)

    anywhere from 0 to 45° out of phase. Initial results showed that out-of-phase rowing was smoother.

    How does the math for that work?

    I'd believe it if six rowers did 120 degree phase angle sine waves with the half wave rectification effect of the up swing being out of the water. I'm not sure that's geometrically possible but it would probably look amazing.

    The problem with admitting engineers to the boat race is you're gonna end up with a weird hydrofoil that uses pedals and an optimized propeller and it's gonna be two times the speed of the other boats until it gets banned by the race officials.

    Google indicates human powered hydrofoil is a thing and 21 MPH is achievable. This strikes me as yet another transportation machine like the bicycle where a lithium battery and brushless electric motor assist unit would help quite a bit.

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  • (Score: 2) by kazzie on Monday June 12 2017, @08:51PM

    by kazzie (5309) Subscriber Badge on Monday June 12 2017, @08:51PM (#524644)

    The boat had 8 rowers, so at 45 degrees the phase of each rower is perfectly distributed (45*8=360) and there'd always be a rower in mid-stroke.

  • (Score: 0) by Anonymous Coward on Tuesday June 13 2017, @02:30AM

    by Anonymous Coward on Tuesday June 13 2017, @02:30AM (#524764)

    > Google indicates human powered hydrofoil is a thing and 21 MPH is achievable.

    Yep, I was part of the group that ran the human powered watercraft speed prizes. We had DuPont as a sponsor and eventually gave away $35K over 4 years, c.1990. I also got to pedal a couple of the different hydrofoils and they were amazingly fun, but also exhausting...they had been designed around the power output of an Olympic-caliber cyclist.