text and images by Linda Welzenbach
All field-based science conducted on board and beyond the Nathaniel B. Palmer would not be possible without the support of the Marine technicians. They are in charge of on-board deck operations, ship to shore operations, and the safe deployment and recovery of scientists, scientific tools and equipment.
Within a day after leaving Punta Arenas, marine technicians Jennie Mowatt and Joee Patterson were tasked with the recovery of a state-of-the-art Autonomous Underwater Vehicle (AUV) that was being field tested in the Straits of Magellan prior to its deployment in the Amundsen Sea.
The pressure is on for the successful launch and retrieval of this “torpedo of science” that can accommodate up to 20 different sensors, including an obstacle detection sonar instrument in the nose cone. The design is based on devices used by the petroleum industry and for national defense purposes; it takes advantage of the AUV’s ability to dive deep(up to 1,000 meters) but with payloads that will measure a variety of characteristics of the ocean, map the seafloor under Thwaites Glacier, and collect information on what is happening at the interface of both—something that was not possible until now. Much was riding on this early test.
The morning of the test was perfect. Cloudless skies were mirrored by the nearly still water of a small cove in the Straits of Magellan. The Hugin, built by the Kongsberg company (who also happen to provide the technology for multibeam bathymetry), is named for one of Odin’s ravens that travel the world to gather information.
Prior to launch, the science team meets with the entire Marine technician support group to go over safety and thesequence of activities. (pic of the big group) Jonas Andersson, one of the TARSAN scientists that manages the Hugin, rolls out the AUV from a specially made garage.
Once the bridle was attached and rigging set to lift Hugin off the ship, Joee and Jennie hopped in the zodiac to prepare for the AUV’s deployment.
With the Hugin in the water, the ship moves away and Jennie and Joee move in to watch over the AUV as it takes on water (shedding buoyancy) in preparation for diving. Once it disappears, they return to ship. Four hours later, the weather has turned ominous. The skies are heavy, dark and spitting rain. The winds have picked up and the sea surface is rough and rolling. Hugin’s bright orange skin is spotted and Joee and Jennie are off in the zodiac to begin the process of bringing Hugin home.
Unbeknownst to those of us observing on deck, the marine technicians (known as the MT’s) had met and devised a plan, to include several contingencies for the AUV’s retrieval based on changes in the environment or equipment condition. The first unplanned situation was the unexpected presence of a South American fur seal who found the AUV interesting.
“The seal was doing acrobatics while we were out there, and I thought it might jump in the zodiac. He came at us quickly and so I scooted the boat away, and then he just disappeared”, said Joee.
Their first step was to attach the bridle system using the hooks on top that would be used to hoist the AUV onto the ship. The plan was that one person would be in charge of maneuvering the lighter weight and buoyant zodiac while the other wrangled the two-ton AUV.
Assuming that the AUV would move more slowly and that the wind and the swells would impact the zodiac, their plan would take advantage of the zodiac’s maneuverability. The goal would be to tie the AUV to the side of the zodiac, which is a typical way of using a smaller thing to tow a larger thing. “Once we got out there, we figured out that our plan where one person did the maneuvering and one person to do the wrangling was not the optimum situation. The contingency was then to tow it astern of the zodiac. This presented other challenges. The Hugin acts an anchor so we have to put a lot of power on the zodiac to get the Hugin to move at all. Then once you get the Hugin moving you don’t want to get it moving so fast that it moves past you. Add to that the swell and wind working against us as we try to keep a heading and keep it trapped behind us.”
Jennie summarized the complexity of the situation, “It was our first time working with the bridle system and we didn’t know how well the zodiac would travel with the AUV. I definitely would not have predicted its hydrodynamic behavior as we tried to tow it behind the zodiac. That was the thing that we couldn’t have predicted until we were actually doing it.”
Following the successful delivery of the Hugin to the deck, Jennie and Joee discussed adding a third person for next retrieval even if the conditions are calmer. “It would be good to have more hands to pull the lines, and to use extra slip lines on the vehicle itself. The weight of the bridal makes it want to sink, so keeping that in the boat will enable better control of the AUV.”
I was amazed at their perseverance and their calm under what was obviously difficult environmental conditions. Yet for the J-Team, it was just another Friday at the office, and problem solving is why they are MT’s for science.