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Rock Candy, Breath Mints, and Bungee Bouncing on the Fantail?!
January 4, 2008 (posted January 5, 2008)
by Susan Humphris, edited by Kristen Kusek

John Bailey, an engineer from Woods Hole Oceanographic Institution, is the type of person that everyone needs on a cruise—especially if there is an engineering problem to be solved. In his 17 years of going to sea, John has compiled quite a list of interesting challenges and savvy, smart solutions. Making his stories especially fun to hear is the fact that so many of his creative solutions have required less-than-sophisticated materials, such as … rock candy!

Ocean science isn’t always about the latest high-tech gadget or sensor. In fact, one time he cooked up a batch of rock candy in the galley (kitchen) and used it to delay the release of a seismometer at the bottom of the ocean—after experimenting to discover that rock candy dissolves in seawater at a rate of about one inch per hour. Rock on, John!

Another story he shared was how he designed and built a very small, highly sensitive acoustic receiver from spare electronic parts on a ship. As if that alone wasn’t impressive enough, he then needed to find a case to protect the instrument. So, he scrounged around and found an Altoids mint box!

Today, John faced yet another challenge to solve. He had to set up a tether (line) and drop weight (sinker) that would enable Puma and Jaguar to descend faster and more efficiently to the bottom of the ocean.

Puma and Jaguar are brand new autonomous underwater vehicles (AUVs). They were first used on a scientific research expedition in July 2007 when they were sent under the ice of the Arctic Ocean to explore another part of the mid-ocean ridgeglossary icon system called the Gakkel Ridge. On that cruise, engineers took the safest approach and programmed the AUVs to dive down to the seafloor under their own power, which takes a lot of time and uses up precious energy.

Another technique that scientists have used successfully with other AUVs is to attach weights, either to the vehicle or onto a tether, which helps them descend faster to the bottom. It also saves energy. Once the AUVs reach the depths where they do their surveying, they drop the weights and continue on their way. But, maybe you can guess the kinds of challenges this method might present. Not only do you need backup ways to release the weight, but you also need clever tether designs to avoid the possibility of the AUV getting tangled up in the tether!

So today, John Bailey’s job was to come up with a “tether and release” design that would work for Puma and Jaguar. John will use two types of releases. An acoustic release that is triggered with a sound signal from the ship will separate the drop weight and tether from the AUV. If that fails, another kind of release will be available within the tether itself—one made of magnesium alloy that would take roughly four hours to dissolve in seawater. (Magnesium alloy is strong and lightweight, and there is lots of magnesium in seawater already.)

The big problem John had to solve was how to release the AUVs over the side of the ship
without putting so much strain on the magnesium links that they break at the ocean surface before the vehicles even start to descend. John’s solution was bungee cord, to add some “spring” to the tether.

This afternoon, John and WHOI geophysicist Rob Reves-Sohn set up a test rig on the fantail (the stern or back end of the ship) using bungee cord, magnesium links, and a weight. Their idea was to let the weight drop so they could see whether the magnesium links would break—which unfortunately was exactly what happened on their first attempt!

After several tries with different combinations of lengths and numbers of bungee cords, they came up with a design that works. Now all we have to do is (GULP!) summon up the courage to try the new tether and drop weight when Puma and Jaguar dive on a mission to the bottom of the ocean. Wish us luck (and keep your fingers and toes crossed)!

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