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Written by Pretender NX01
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Saturday, 19 August 2006 |
Whirlpool of Death
Episode #56
Original Air Date: July 26, 2006
The Myth: A swirling vortex can develop in the water that is large enough to pull down a swimmer or even an entire ship.
The Expert: Hector Quinones of the San Francisco Coast Guard
Mythtern: Jess Nelson of the “Archimedes Burn-off” women’s team
Memorable/Quotable Moments:
Adam: “Here’s a little boat unsuspecting on the high seas. Here’s a whirlpool. Oh no! That would be bad.”
Adam: “It’s the toy every kid wants, a container ship. Gee, thanks Dad! Now I can recreate international commerce”
Adam: “I know there’s going to be payback, but I just couldn’t resist”
Jamie “You’ll never know”
Jess: “Smells like pizza”
Action/Results:
Part 1 of this myth is that a ship can be sunk inside a whirlpool. Adam and Jamie set out aboard a Coast Guard ship to see actual whirlpools as they develop near the pylons of the Golden Gate Bridge. A vortex develops when opposing water currents intersect and start to swirl creating the whirlpool which can swirl down hundreds of feet. The whirlpool vortices observed do not pose any threat to ships, as Jamie notes, however they could be troublesome to a swimmer that was caught in one.
Back at M5, Adam and Jamie determined they should first test ways of creating water vortices in small scale models before attempting to create a full scale model. Jamie suggested using a paddle wheel to create a whirl pool in a small container whereas Adam suggested using water jets and a recirculation system to create whirlpool vortices in the container. Adam used a small pool pump along with a container with a hole in the bottom of it to suck water out and then circulate it back in which then creates a conical vortex in the water. Jamie used a cordless drill with two metal blades attached to the end to spin at the bottom the container until a 9 inch vortex is created. Both methods work in the small scale build.
Next they scaled up the model size to a slightly larger container; Adam’s method creates a vortex 14 inches in diameter going all the way to the bottom of the container while Jamie’s method now requires 15 amps of electricity to create a vortex. Adam and Jamie then moved on to a 50 gallon tank. Adam discovered he only needs to move 25 gallons per-minute to create a vortex using his method. Jamie’s device used 8.5 volts of power and still only creates a depression in the water and not a full whirlpool. Adam’s method was then chosen for the full scale build which he said experts confirm is the best way to recreate a whirlpool occurring. Adam created a scale person out of foam, to simulate a swimmer who is completely buoyant, which is sucked down into the vortex. Adam noted that’s like falling into a cone of water 10 feet deep.
Fact: The largest whirlpool is located near Deer Island Point in Canada. The vortex is 200 feet in diameter and turns at a speed of 14 knots
For the full scale build a 9000 gallon tank is required along with scale models of a container ship and a fishing trawler. Adam and Jamie need to go to a dive shop to get the equipment that Adam used for his test simulating a swimmer caught in a vortex; so the Mythbusters call upon Jess Nelson of the “Mailbag Special” to assist in making the model ships including leveling them off and filling them with lead shot so they displace the proportionate amount of water for their size. The container ship is 1: 500 scale, while the fishing trawler is 1: 50 scale.
At the dive shop Adam suggested testing out the equipment that includes an emergency air supply. In the pool Jamie tugged and twisted Adam underwater while Adam attempted to quickly get to his air supply. After testing, the duo headed back to the shop.
The Mythbusters set up their specially built 16 feet tall (and 10 feet wide) tank upon railroad ties so they could fit a large pipe beneath it to drain the water through a construction pump that is capable of moving 35 gallons a minute out of the tank and then circulating it back into the tank through another pipe.
Jess started filling a 2,000 gallon water truck from a hydrant and then used the truck to fill the tank which required several truck-fills and takes a few hours to fill. The water pump system was switched on and a whirlpool developed that churned at a speed of 14 knots, which is 42 revolutions per minute. When the whirlpool was scaled down to the size of the trawler ship, it only turned once a minute, and for the size of the container ship it would only turn once very ten minutes. Adam and Jamie then decided to do a worst case scenario and see how big a whirlpool would have to be to bring down the ships.
A container ship is 1,000 feet long and travels at 230 miles per hour. The whirlpools used to sink it would scale up to be swirling as fast as Mach 3 and be half a mile in diameter. The trawler which is about 70 feet long in real life would requires a vortex speeding at 100 knots and be 150 feet in diameter. Neither of those vortices could be generated in any oceans on earth. The verdict is that the myth of a whirlpool sucking down a ship is BUSTED.
Part 2 of the myth is that a swimmer can be caught in side a whirlpool. Adam suited up and got into the tank. While holding onto a trapeze the pump was activated and a vortex formed around him. Adam started spinning and said he felt like he was being pulled down. Adam and Jamie said that a swimmer caught in a vortex swirling at 14 knots could be pulled under. Jamie suggested they test the whirlpool a second time to actually see Adam go under. The second test is halted during testing as Adam begins to feel sick. The churning then causes Adam to vomit which Jess notes “Smells like pizza”. The verdict is that the myth of a swimmer being pulled under water inside a whirlpool is PLAUSIBLE.
Myth: A snowplow driving down on a freeway at high speed can create enough air pressure off of the plow to push over car driving along side.
The Experts: Snowplow mechanics Pat Manning and Matt Edgeman
Memorable/Quotable Moments:
Grant: “Make no mistake, this is a deathtrap”
Kari: “Considering the man-hours, wouldn’t it have been a lot cheaper to get a truck for $1,000 that all the wheels rolled on?
Robert Lee (Narrator) “Normally the Mythbusters stop vehicles by running into things. They are the collision kings”
Kari: “That was 20 miles per hour”
Tory: “And we almost killed him”
Tory: “I guess that would be 100% carnage”
Grant: “I forgot to activate the brakes”
Action/Results:
First, Kari and Grant decided to see how much force was required to flip over a car. Tory had brought in a vehicle with a high center of gravity, low wheel base, and a lot of surface area in addition to being light weight. Tory lassoed the car and attached a force gauge and used a truck to pull the car until it tipped. Kari worked out that the force gauge listed 1,000 lbs of pressure combined with the surface area means it will take .21 pounds per square inch (PSI) to flip over the car.
Next the build team decided to find out how much PSI was generated by Jamie’s truck traveling down the highway. Kari built a pressure gauge consisting of a tube filled with water and which used an anemometer to determine wind speed. Traveling at 65 mph gave a half inch reading and gave only one sixth of the force required to push over the car. Tory noted that, while a passing semi can generate enough of a blast of air to shake his car, it’s never blasted him off the road and if a semi can’t do it he didn’t feel a snowplow could.
The build team get a free snowplow that is no longer in working condition. Part of their work required cutting the drive shaft to free the wheels from the now rusted gearbox. Also a number of rodents are found to be living in the plow. During the first attempt at towing the snowplow Kari noticed one of the wheels isn’t tuning, instead it was just scraping along which would skew the results if it couldn’t be fixed. The first attempt ended after traveling only 50 yards.
After almost two days of work the build team removed the wheels and gotten the plow moving. Next the team tested the brakes of the plow since this vehicle won’t be stopped in the usual way of crashing into something else. The only way to test plow’s brakes is to tow it along and have someone (Grant) test the brakes. Kari felt that something seemed dangerous and Tory stated that they should only test the brakes at 20 miles per hour and not at the 70 mph that had been planned. Grant was wearing a crash helmet and safety harness, while Troy and Kari towed the plow behind their truck. Both the plow’s brakes and the emergency brake fail and the plow ran over the tow chain causing it to veer sideways before coming to a stop.
The build team called in experts Pat Manning and Matt Edgeman who bled the brake system and get it in working order. For the actual test Grant created a remote control breaking rig that used a linear actuator to press down on the brake pedal when he pressed the trigger.
The plow and car being tested were hooked to 1500 feet of towing cable that was threaded through a system of pulleys so that the car towing them would be driving away from the track. The first test of the newly fixed brakes had Kari towing the plow behind a car that only is able to speed up to 45 miles per hour. Grant used his remote control but the snowplow fails to brake and crashes into the barricades at the end. Tory suggested they build a wall of sandbags to stop the plow even after Grant’s work on the remote control device.
To save time the Build Team decided to forgo testing both a regular snowplow size and then creating a larger one and just skip ahead to building the largest plow drivable by attaching a steel frame and plywood the to plow’s scoop. The increase in size does increase the plow’s drag but, even though the speed of the car and the plow was increased to 60 miles per hour on the track and they passed each other within a few feet, yet the plow failed to affect the passing car.
The snowplow then continued on and crashed into the barricades at the end of the tracks. Tory said that it’s not a bad thing because they proved that a passing plow did not have any affect on the other car before the plow was totaled. During cleanup, Grant confessed he “forgot to activate the brakes”.
Tory said he’s glad Grant forgot to activate the brakes because he liked seeing the snowplow destroyed. The build team then used a crane to lift up the plow and drop it, demolishing it even further. Back at M5 The Build Team discussed with Adam that their verdict is that the myth of a plow blowing a passing car off the road is BUSTED. They also said they don’t feel the need to revisit this myth. “Don’t write to Tory about this one”, said Adam.
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Episode Descriptions 
