Mathematician solves rowing boat "wiggle" problem | Hacker News Reader

Mathematician solves rowing boat "wiggle" problem

technologyreview.com

49 pointsypavan12 comments

> the serious problem of oscillating non-zero transverse moment in racing boats, otherwise known as wiggle.

Thank goodness for simplification of terminology.

I rowed in college, we experimented with different riggings (including arrangement 'a' from the article) and found that, indeed, bucket-rigging and others seemed to yield good times. There were other variables though, strength of the current, wind, how intense our hangovers were... so it's hard to attribute it to just the different arrangements. I will say that sitting in an arrangement where the guy in front/behind has his oar on the same side as you leaves very little room for error. If you don't get that oar up and out at the finish you'll hit oars and crab for sure.

Why would the current matter? Assuming the boat and oars are all in it?

The start and finish of the race are located at fixed points. If you're racing on tidal rivers near the coast, where most of our regattas were, the current varies widely throughout the day. Say it's a 5k head-race starting upstream and coming down towards the sea. At high and low tide you're essentially racing with no (or very little) current - much like a lake. When the tide is coming in, you'd be racing against it and a 5k race can take 20 or more minutes. If you're lucky and your race heat starts when the tide is going out, that same race will take 15 or less minutes.

There are several considerations that a rowing coach must make when deciding the rig of the boat as well as which rowers should occupy each seat.

These considerations may vary for each rower and include:

1. arc length (i.e. the distance traveled by the blade of the oar)

2. force curve (i.e. the amount of force applied during each part of the time the oar is in the water)

3. boat feel (it is a much different sensation rowing in the bow, middle and stern of the boat and different rowers are "better" in different parts of the boat)

I wonder if some of those rigs are more fragile than the others. Perhaps some of them (rig (a) perhaps?) would wiggle more severely if the rowing forces were uneven while others would be fairly robust to differences in force.

I wouldn't expect so, at least by the math. It looks is pretty simple. Number the seats 1 to 8, then for each side sum the seat numbers. The standard rig gives 16 and 20, but all 4 of these solutions are 18, 18.

"to show that the balance of forces in this rig as the oars are pulled through the water"

If the oars are pulled through the water, the boat wouldn't move.

What do you mean?

I suspect his point is that the blades of the oars, when immersed in the water, don't move (much) relative to the water. Approximating the blade as stationary in the water, we can see that the boat moves because of a lever effect. If the oars moved freely through the water there would be no thrust, as would be the case when rowing in liquid helium.

However, given the context, it seems a singularly pointless nitpick.

Especially considering that, in practice, oars move quite a lot through water. It’s fluid, after all; rowing is not like ski-poling yourself along.

The oars move more than a little through the water. It isn't the immutability of the water that allows for traction, it is the drag, or perhaps resistance is a more appropriate term, that gives bite to the oars in the water.

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