Episode 56: Killer Whirlpool

Air Date: July 26, 2006

A tidal whirlpool can sink a container ship.

busted

In order for this to happen, the whirlpool would have to be significantly stronger than any maelstrom ever recorded.

A tidal whirlpool can sink a fishing trawler.

busted

In order for this to happen, the whirlpool would have to be significantly stronger than any maelstrom ever recorded.

A tidal whirlpool can sink a person.

plausible

A whirlpool can generate a vortex large enough to pull down a swimmer and, especially if combined with the effects of dizziness and disorientation, induce drowning. The MythBusters only tested according to the most powerful maelstrom ever recorded, and did not determine the minimum size needed to submerge a swimmer.

A snowplow passing by at high speed can displace enough air on one side to flip over a passing car.

busted

Even a worst-case scenario – an unusually large plow passing by a light, top-heavy sports utility vehicle at highway speed – could not generate the air pressure needed to cause the SUV to even visibly tip. A semi driving at highway speeds only generates about 1/6th of the air pressure needed to make this myth plausible.

29 Comments

  1. Anders says:

    “Saltstraumen” near Bodø in Norway is very dangerous, obvious due to the tidal whirlpools and powerfull streams. One will be pulled under water and drown.

    I don’t know the criterias for this test. Maybe you should reconsider.

  2. John Trev says:

    One query about the methods in this test..
    When the speed of the whirlpool was calculated, scaled-down *distance* was used but not scaled-down *time*.
    For example, a speed of 100 m/s scaled down by 1:100 was assumed to be 1 m/s because 1m = 100 scaled-down meters. But shouldn’t it be (100 scaled-down meters / 1 scaled-down *second*)?

    I’d suggest using something like multiplying time by the square-root of the scaling factor. So 100m/s scaled down by 100 should be (100/100)m / (1/10)s or 10m/s. Much faster than the apparent test method, which could add plausibility to this myth.

  3. Brian says:

    100 meters per 1 second is the same thing as 1 meter per 1/100 of a second. It wouldn’t be scaled down at all. They did it right.
    (The same principle works if you don’t slow time down as much as distance. It’s still faster then it should be. The right way to scale it down would be to scale down the ship. Which is what they did.)

  4. Z says:

    Not busted because Lake Peigneur, Louisiana incident in 1980 actually sucked in an oil rig and boats.

  5. Sean says:

    The Lake Peigneur whirlpool wasn’t tidal. It was the world’s largest bathtub drain. It’s a different phenomenon.

  6. Bruce Browne says:

    Re: Snowplow passing at high speed can displace enough air to flip a passing car.
    Many people have witnessed a pull or negative pressure from a passing plow or transport truck. This test was not busted, as your plow is creating a positive pressure. You are faceing the blade in the wrong direction! Obvious you have never plowed snow before. Most plows throw snow off the road. Not that it really matters but it could be possible for a car to loose control if the driving conditions were icy with -40 degree dense air, with a driver slightly overcorrecting. The car was also pulled rather that pushed towards the plow which helps stabilize the car. Sorry, Your Busted.

    • Kint Verbal says:

      Very much depends on speed, as air displacement increases by the third power vs. the speed increase. So if their highway speed X generated only 1/6 of the force, this means 1.8X speed would generate something close to the full force required.

    • Matthew Lobdell says:

      I agree with you. They do need to rethink how they did the experiment. And get it all the way it should be.

  7. Dick v. A. says:

    Actually John Trev is absolutely right. Many years ago, while playing with toy trains, I noticed they were going absurdly fast. My father proposed that time should be scaled so that the scaled acceleration of gravity should be constant – and that indeed means that if you use a 100 times smaller model, time should move 10 times faster. Work it out!

  8. Joe Magnan says:

    I don’t know but I think you have this myth kind of miss-stated.
    Shouldn’t it be “A snowplow passing by at high speed can displace enough snow on one side to flip over a passing car.” ?

  9. Michael Carnevale says:

    You did the snowplowing myth all wrong. You should have the plow and the truck going in the same direction, with the car possibly stationary, the snowplow passing the car on the left while plowing snow. You had the plow facing the wrong direction when you did it. So your BUSTED.

  10. trevor says:

    I missed most of this episode but the road they were travelling was it icy or dry obviously that would make the difference. You usually only see snow plows after a storm.

  11. bob miccoli says:

    In regards to tidal vortex, look up the Knox Mining disaster near Pittston , PA.It happened in 1959 when coal miners dug too close to the river.they tried to plug the hole by dropping railroad cars into the vortex.Maybe not a “tidal vortex’ but a great illustration of the force of water.A short video exists showing the event. More info can be obtained from The Lackawanna Coal Mine Tour in Scranton , PA
    Bob

  12. Andrew says:

    I really think the snow plow myth should be revisited. I compleatly agree that the test peramiters were all wrong. First thing I noticed was that the weather was all wrong, I have passed big trucks and snow plows on a nice calm clear day too and didn’t even notice anything, icey roads or not, its the wind that makes the differance. If you had a tail wind of 100 km/h, which isn’t unheard of in southern alberta, and you met an oncoming snowplow going 115 km/h that would mean that truck is moveing through the air at 215km/h. believe me you sure feal that in what ever kind of car or truck you are driveing.

    • Kint Verbal says:

      See my above comment regarding relationship between speed and volume of air dislocated.

      That said I would not expect a snowplow would never drive 115km/h, especially against a 100km/h wind! It most likely simply doesn’t have enough power.

  13. Dick Veldkamp says:

    Distance/time scaling.

    For the scaling to be right (i.e. the flow problem resulting in the same Navier-Stokes equation) two numbers should remain the same:

    Reynolds number Re = rho U L / Eta
    Froude number = Fr = U / Sqrt(g L)

    g = gravity’s acceleration = 9.81 m/s2
    L = ship’s length [m] (and vortex dimension)
    rho = water density = 1000 kg/m3
    U = speed [m/s]
    Eta = water’s dynamic viscosity [Ns/m]

    Supposing we have only speed U and dimension L to play with, clearly we cannot keep both Re and Fr constant, because that would mean that simultaneously:

    U L = c
    U / Sqrt(L) = c

    I don’t know offhand which number is most important in this case, but my guess would be Fr because a vortex shape has to do with speed and gravity (we may usually allow Re to vary within a decade without significantly changing the problem)

    This would mean that we have to scale down speed U as the square root of the dimension L.

  14. Persojet says:

    for the snowplow thing could you test the myth with snow conditions and not in “summer”

  15. Mr.Woob says:

    Lake Peigneur was considered a whirlpool. If you can show me one definition of a whirlpool that does not simply state a circular current of water that near by objects are drown into then I retract my statement. Everything I found considers it a whirlpool and it did happen. A lake went from 10ft deep to 1500ft deep. That is a crazy bathtub and I cannot find any other “bathtub” like it.

  16. Tristan says:

    I would love Mythbusters to bring back the Whirlpools. As a whitewater kayaker I am around moving water all the time. I think it has to do more with volume of the water and a bit of geography, what the water is being forced through or around, as we know this and gradient is what forms rapids and other features such as whirlpools. The ocean is a bit of a different story since the gradient, more or less, is the tide going in and out. But Tidal rapids are still formed by compression, all that water between a few islands at 14 knots…something is going to happen.

    A whirlpool can definitely drown a person, one river I work on this has happened. On this same river I have gone for a few rides for a number of seconds underwater in a 70 gallon kayak. The best example I have seen to illustrate a “Killer Whirlpool” would be Skookumchuck Narrows near Vancouver Island in Canada. Here I have seen people in their kayaks disappear for 40-50 seconds!(they lived but didn’t get back on the water) Yes, still no ship but definitely impressive and scary.

    There are rarely whirlpools that will sustain their shape or position…they usually come and go. But it is possible to go from one whirlpool to the next. This I have experienced in smaller whirlpools on another river I work on, a fun little spot to voluntarily jump into the whirlpools for a 10-30 second ride ( underwater with a PFD on). These whirlpools are only about 3-4 feet in diameter and I wouldn’t doubt this could drown someone without a PFD or Lifejacket on. There is also a crazy sport out there called squirt boating. Where you are in a kayak that has extremely low volume and they are designed to be pulled down by an eddy line or whirlpool. I have seen these kayakers disappear for 10-40 seconds on purpose and apparently the longer you are underwater the better.

    In the end could whirlpools sink a ship? A tanker well highly improbable but a fishing boat, sink yes, pull the boat underwater instantly, very unlikely. I would love to see the dust blown off this myth for another go.

  17. Oslofyr says:

    The worlds largest tidal worldpool is not in Canada, but Saltstraumen in Norway.

    Bad research, boys.

  18. Justin S says:

    Mythbusters should redo the Snow plow with car myth
    I live in wisconsin and during are winter session we get 60 to 90 mile per hr winds, if you add wind to the factor with going 70 miles per hr on the road you will flip another vehicle, with all that wind being forested against the blade of the snow plow angel towards the car the force will tip a light weight car over.

  19. Robert Godfrey says:

    I measured one Old Sow Whirlpool vortex by using an aerial photograph, extrapolating the diameter by comparing it to the 6-foot diameter beacon tower at the shoreline. That individual vortex was approximately 250-feet/76 metres in diameter.

    There was a larger, less-well-defined vortex near the one I measured.

    Old Sow Whirlpool is generally considered to be the second-largest in the world, and the largest in the Western Hemisphere; however, I have not seen dimensions of any other of the five major whirlpools in the world. Whirlpool size can also refer to the general area of disturbance, rather than of an individual vortex, so nailing down size can be largely subjective.

    Robert Godfrey
    President
    Old Sow Whirlpool Survivors Association
    Eastport, Maine, USA
    http://www.oldsowwhirlpool.com/

  20. TJ says:

    hmm… if you multiply (c) by (FL) you have enough force to sink (R) the fishing boat. bad research boys

  21. Matthew Lobdell says:

    Does anyone know what car they used in the snow plow part?

  22. Lawrie says:

    I don’t know if any of you have been to northern Westen Australia. There is a very norrow enterance to an inlet there called “the horzonal Waterfall”. this area creates very powerful whirlpools. that can suck small size boats(48ft)under in no time. As for the speed of these whirlpools is yet to be measured.

  23. Rick Box says:

    OK, so there’s a lot of disagreement about the physics.

    How about if the Mythbusters *test* if the scaling is valid? Edgar Allan Poe claimed, in a short story, that a small boat (or barrel), survives in a maelstrom better than a ship.

    Test if a smaller model or a larger model fare differently in the same vortex. I think the whole scaling thing is invalid.

    A large model and a small model will fare the same, just as a penny and a bowling ball don’t fall at different rates. If that hypothesis is tested and correct, then the model should go at the same speed as in an actual full-size maelstrom.

  24. garyB says:

    The Mythbusters have done later work with scaling and have learned more proper methods. They should re-visit the killer whirlpool with this new knowledge.

    Regardless of the velocity/size scaling, the plastic models they used were infinitely stronger than a real ocean going vessel. Even if one had the means, real ships cannot be lifted out of the water by grasping one end. In dry-dock the hull must be carefully supported so as not to break the back of the ship under its own weight. At sea, a ship hull even flexes over average ocean swells.

    It seems the hull of the model ship should have been made with aluminum foil coated with something rubbery such that it would bend and deflect under its own weight. A simulated cargo, like dry sand which adds nothing to the hull strength, should also be used.

    Just some thoughts….

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