
A 127-year-old physics riddle regarding the Kelvinangle in boat wakes solved - Errorcod3
https://phys.org/news/2019-08-year-old-physics-riddle.html
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ramshorns
> _" Fuel consumption can double if the vessel is traveling downstream
> compared to upstream," Ellingsen said._

This is counterintuitive. The fact that it's easier to make waves traveling
upstream must outweigh the fact that if you're going downstream the water, you
know, carries you.

~~~
Retric
Fuel consumption in boats is usually measured at some speed relative to the
waters surface, not the earth.

~~~
ptaipale
Or relative to time (litres or kilograms per hour).

~~~
Retric
Time on it’s own is not enough as the faster the boat goes the more fuel it
consumes per hour.

That said, at each specific speed you get a rate as x gallons per hour.

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davidhyde
Can someone please explain to me why this is so groundbreaking? If I blow a
smoke ring and there is no wind my smoke ring stays circular. If there is wind
blowing from the side my smoke ring will become distorted. Likewise if there
is a current in water then I expect that current to disturb the propagation of
waves moving through the water, not so? The medium in which the wave is
propagating is itself moving.

Surely this has not remained a mystery for 127 years.

~~~
lexicality
The news is that someone worked out the maths behind it and wrote it down -
then proved they were right.

It's a bit like the fact that everyone knows the shower curtain will billow
towards them in the shower but no one has managed to prove why that happens.

~~~
phkahler
Because the hot air inside rises and cooler air pushes inward. It's called
convection, and I don't thing anyone needs to run a simulation and publish a
paper solving the "shower curtain problem" just because it hasn't been "done"
before.

~~~
thaumasiotes
It has been done before. See the physics winner for 2001:
[https://improbable.com/ig/ig-pastwinners.html](https://improbable.com/ig/ig-
pastwinners.html)

~~~
lexicality
I like that it took him two weeks of compute time and it's only a "partial
solution"

~~~
thaumasiotes
That's fluid dynamics for you. :-/

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ragazzina
Other interesting physics riddles solved after some time:

[https://en.wikipedia.org/wiki/Feynman_sprinkler](https://en.wikipedia.org/wiki/Feynman_sprinkler)

[https://en.wikipedia.org/wiki/Blackbird_(land_yacht)](https://en.wikipedia.org/wiki/Blackbird_\(land_yacht\))

And the infamous plane on a treadmill..

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horsawlarway
I hate the way this article is presented.

It takes an interesting and intuitive effect that we couldn't explain
mathematically and now can, and tries as hard as possible to shove every
fucking clickbait word in as possible.

Kudos to the author for presenting this material in possibly the least
consumable way imaginable. I hate it.

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alok99
I understand that there is now proof of the usual V-shaped wake angle not
always being ~39 degrees depending on subsurface currents.

I'm a bit confused about the ring waves part of this article. How is the boat
leaving a ring wave when it moves? Or is the boat just being lowered into the
water to form a ripple? You can't tell this from the top-down view.

For some reason, the way that the article was written made it seem that a boat
moving through the water could leave an off-center ring wave wake, which makes
no sense.

~~~
skykooler
A wake is essentially a ring wave which is being continuously generated by a
moving point. If a ring wave can be generated off-center, the wake will also
be off-center.

