Upgraded Alvin submersible sets sail

You would think that a little sub built almost 50 years ago would be sitting in a museum somewhere, but Deep Submergence Vehicle (DSV) Alvin, which launched in 1964, is still going strong. Owned by the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI), Alvin has completed a major US$41 million redesign and refit. The revamped submersible set sail on Saturday aboard its mothership R/V Atlantis for certification testing off the coast of Oregon and California.

Alvin’s certification tests are the end of its “Phase One” upgrade, which began with a redesign back in 2005. The little submersible, capable of carrying a crew of three, is hardly recognizable as the same craft that was built by General Mills in the 1960s. The refit has increased Alvin’s weight from 35,200 pounds (15,966 kg) to 45,000 pounds (20,411 kg) – more than 40,000 pounds of which is a brand new titanium personnel sphere designed and forged by the Southwest Research Institute. Its three-inch thick walls were forged and then welded together with an electron beam, allowing it to make descents to depths of 21,000 ft (6,500 meters) and has been tested to the equivalent of 26,000 ft.

In addition, the new sphere is 4.6 inches wider, which may not seem like much, but it increases its volume from 144 to 171 cubic feet (4 to 4.8 m³). This not only makes it more comfortable, but it also makes it possible to increase the number of viewports from three to five with overlapping fields of view.

Other improvements to Alvin include increasing the science payload from 200 to 400 pounds (91 to 181 kg), the installation of better exterior lighting, a high-definition imaging systems and an improved command and control system.

One example of the challenges faced in refitting Alvin is the new syntactic foam fitted to the submersible’s interior. Like many watercraft, it uses plastic foam to give it buoyancy, but conventional foams, such as Styrofoam, are buoyant because they’re full of air bubbles. At a depth of four miles, the water pressure would squash air-bubble foam into a hard mass of plastic. The syntactic foam used by Alvin replaces the air bubbles with microspheres made of glass or some other material, so it takes a lot more pressure to compromise the foam.

Alvin is regularly disassembled every three or four years and has undergone a number of refits over the decades. In 1973, its original steel sphere was replaced by titanium, manipulator arms have been added or replaced on a number of occasions and, in the 1980s, its rear propeller was replaced by a set of thrusters and new batteries installed. Because Alvin is much heavier after this latest refit, R/V Atlantis also had to undergo a refit with a strengthened A-frame to handle the heavier craft and a larger hanger for it.

Named for WHOI scientist Allyn Vine, Alvin is the world’s longest-operating deep-sea submersible and has completed 4,664 dives. During its almost half a century in service, it has been involved in a number of historic events, such as the recovery of a US Air Force hydrogen bomb in the Mediterranean Sea off the coast of Spain in 1966, exploring the first known hydrothermal vents in the 1970s, surveying the wreck of the Titanic and studying the aftermath of the Deepwater Horizon oil spill.

Even Alvin’s accidents have been serendipitous. In 1968, the submersible was dropped into the ocean when a cable snapped. The sea rushed into the open hatch and, though the crew escaped, Alvin sank in 5,000 feet (1,500 m) of water. Recovered a year later, the craft not only showed very little damage, but the lunch packed for the crew was soggy, but still edible. According to WHOI, this sparked new research into the environment and biology of the deep ocean.

Alvin will undergo US Navy certification in September with a series of progressively deeper dives off Monterey, California. It will then carry out a science verification cruise in November to test its scientific equipment and, if everything checks out, will return to service in December. Though its new sphere allows Alvin to dive to 21,000 ft, it will only operate at a maximum of 15,000 ft until its Phase Two refit is carried out. This will see the addition of new lithium ion batteries that will increase its operating time to up to twelve hours.

Alvin is scheduled to reach Astoria, Oregon on June 20.

Source: Woods Hole Oceanographic Institution