Episode 192: Hail Hijinx

Air Date: October 21, 2012

It is possible to jump to safety on a collapsing rope bridge.

busted

This myth is based on a scene in the film Cliffhanger in which Sylvester Stallone’s character is able to make a running leap to one end of a rope bridge after the mooring at the opposite end of the bridge is destroyed with explosives.

Adam and Jamie built a small scale bridge and a pneumatic “jumper” to begin their tests. Electronic timers controlled the jumper and controlled a solenoid that dropped one end of the bridge. A control jump (without dropping the bridge) resulted in a jump height of 22 inches (56 cm). With a 50 millisecond delay after dropping the bridge, the jump height was 10 inches (25 cm) and with a 100 millisecond delay the jump height was 4.5 inches (11 cm). With a 150 millisecond delay the jumper was no longer able to jump from the falling bridge.

Adam and Jamie then built a full scale, 1600 lbs (725 kg) bridge with pine boards and steel cables. They strung the bridge across a large dry dock in a ship yard. Quick releases with small explosives (squibs) were used to release one end of the bridge. To test a running leap, Jamie began several strides from the safe side of the bridge as the other end was dropped. The bridge went slack immediately and Jamie fell with it because he had no footing to jump from. Next, Adam attempted to make a smaller, standing jump. He stood at an achievable distance and waited for the sound of the explosion before he jumped. The bridge fell before Adam even had time to react to the sound; he was not able to jump at all.

At this point the myth was busted but Jamie wanted to see if it was possible to hang on to the hand ropes as the bridge fell. He was successful in holding on but was not able to climb all the way back to safety. He suggested he might be able reach the top if his life really depended on it.

A violent hail storm can sink a boat.

plausible (barely)

To begin their tests in the shop, the Build Team fired large, baseball-sized spheres of ice at boat hulls from a compressed-air cannon. They began firing the ice at 80 mph (123 km/h) to simulate terminal velocity. At this speed the ice did not puncture an aluminum, fiberglass, or a wooden hull. At 150 mph (241 km/h) (simulating hail in a hurricane) the ice still did not puncture any of the hulls. At 300 mph (483 km/h) (the fastest recorded tornado speed, even though hail isn’t typical in tornadoes) the ice only penetrated the weakest areas of the wooden hull. At this point the myth was described as busted but the team decided to continue these tests with the boats actually floating on water. On water the ice did not penetrate the fiberglass hull even at 300 mph (483 km/h). With the wooden hull, the ice penetrated at 300 mph (483 km/h) and 150 mph (241 km/h), but not at 80 mph (123 km/h).

The Build Team also reasoned that hail could potentially sink a boat by filling up its volume with enough extra mass. At a port they began filling one of their small boats with ice. The boat only began to sink after 4,000 lb (1,814 kg) of ice was added. The boat did not sink entirely because the ice began floating and supporting its own weight when in the water. Because this myth appeared to be possible in extreme situations, it was deemed plausible.

11 Comments

  1. Mary says:

    It is clear that the cast members are not from country where they regularly get hailstones. During a hailstorm there is not going to only be one hailstone hurled at a boat, there are going to be hundreds. A boat would get a hole in it after being hit repeatedly with the hailstones. Also, a hailstone that’s a couple inches is nothing compared to the largest hailstone being 6-8 inches in diameter. Try again Mythbusters.

    • A Guy says:

      My thoughts exactly. I was rather annoyed when watching the episode when they drew a conclusion after launching only 1 hailstone at each boat.

      • Marc-Andre says:

        If one ball of hail can remove some chips of woods on that boat at 100 mph what about a hundred ?

    • Marc-Andre says:

      I was going here to say the same thing. I have been in Hail storms and you don,t have a single ball of hail and on the plus side we have the erosion factor of having multiple balls of hails at the same spot multiple times and at multiple places augmenting the probability of finding a weak spot for sinking.

  2. Susan says:

    Another problem with the hailstorm myth: since when has anyone ever seen a violent hailstorm without high winds, and therefore waves? Lower the freeboard on the boat enough with ice, and the waves will swamp it. It would also depend how much built-in flotation the boat possessed as to whether it would sink once swamped.

  3. Kai says:

    My biggest concern about the test with the hail is that the wooden boat lab shot was a bit of an unfair test in my eyes.
    There are two main parts of a boat, the hull and keel. The keel is the thick spine of the boat, while the hull is the thinner area between the ‘ribs’ of the boats cobstruction, every shot (apart from the penetration 300 mph which hit the hull) was hitting the keel, the thickest part of the boat by between two or three times the thickness of the hull if not more,
    The part of the boat most likely to be penetrated? The hull of a wood boat, and in the lab tests? No shots on the hull, the weakest and most likely area to be hit by hail (due to the fact the hull is everywhere there isn’t keel or rib of the boat)
    I don’t know how much it would change the test but hitting the hardest area of the boat might not be the best target, since hail will hit every part of a boat, not just the thickest area

    • Corey says:

      Agreed. The fact that they were hitting the ribs of the wooden boat drove me nuts. I know it’s just a TV show, but if you’re going to take the time to act like you’re adhering to scientific methods, you can at least remove the most obvious variables. They did not hit the ribs of the metal or fiberglass boats and they shouldn’t have on the wooden boat. Not to mention, if you are testing for plausibility, you want to give the tests the greatest chance for success. Assuring that the hail hits the thinnest part of the hull on every counted test would seem like a main requirement of the tests.

      I watched the after-show video where this issue was asked and answered. Grant flippantly responded with an excuse in the form of a challenge “you try to build a hail cannon and aim it.” Everyone chuckled, as they so often do in the party atmosphere of the after-show, and that was it. Ugh! The point was missed and dismissed. We watch the show because these people have the funding, through our viewership, to take the extraordinary steps to build these impressive contraptions and take the time and effort to perform these tests. Grant should be applauded for his efforts with the hail cannon, but shouldn’t they consider taking additional shots after re-aiming the cannon so that his efforts aren’t in vain!?

      Glossing over such huge deficiencies in the testing method completely ruins that segment of the episode for me and my interest in the show goes down a notch.

      They take the time to drag in these various boats. They take the time to retest because of hitting a rotten part of the boat. They take the time to go out to two different locations with water for various tests that involve heavy equipment. However, they can’t take the time to reposition the wooden boat by a few inches and reload the cannon!? I don’t get it. What am I missing?

  4. napsa says:

    In movie cliffhanger, the bridge doesn’t collapse at the same time with an explosion. And when it’s zoom’s out you can see that Stallone is allready jumped, when brige collapses. Yes, he runs when the explosion happens, but the bridge does not collapse immediately.

  5. Richard says:

    The other thing that needed to be considered is that hail is not as uniform as they made it. In fact large hail has spikes and lots of irregular features.

    These can easily change the penetration factor.

    They could have also confirmed they technique by trying it against something known to breakage by hail (like a windshield)

  6. Mark says:

    I don’t know if this would have made a difference but as a meteorologist who knows about hail, hail is made up of many layers of ice. It’s not just one chunk of ice.

    • Stephen says:

      Correct.

      Real hail is really hard.

      It also does not shatter into tiny pieces like in the tests conducted by the Mythbusters.

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