from Hacker News

A 127-year-old physics riddle regarding the Kelvinangle in boat wakes solved

by Errorcod3 on 8/21/19, 12:25 PM with 43 comments

  • by ramshorns on 8/23/19, 10:45 AM

    > "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.

  • by davidhyde on 8/23/19, 9:52 AM

    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.

  • by ragazzina on 8/23/19, 2:22 PM

    Other interesting physics riddles solved after some time:

    https://en.wikipedia.org/wiki/Feynman_sprinkler

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

    And the infamous plane on a treadmill..

  • by horsawlarway on 8/23/19, 3:31 PM

    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.

  • by alok99 on 8/23/19, 4:05 PM

    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.