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Marine Electronics


August 2012 Issue

Chinese Manned Submersible Breaks 7,000 Meters in Dive
The Jiaolong, China's manned submersible, reached depths of 7,020 meters during its fourth dive into the Mariana Trench in the western Pacific Ocean in June.

During the 11-hour dive, the oceanauts worked for almost three hours on the seafloor, placing markers and collecting water samples and sediments, state-run news agency Xinhua reported.

The Jiaolong had succeeded in reaching depths of 6,671 meters, 6,965 meters and 6,963 meters in its previous three dives from June 15 to 22, surpassing the record of 5,188 meters it set last July. Submersibles from Russia and Japan have reached depths of 6,000 meters.

Chinese officials have said the aim of the Jiaolong operation is to develop ocean-resource management and exploration.

The submersible was scheduled to attempt two more dives into the Mariana Trench and was expected to return to China in mid-July with its oceanographic mother ship Xiangyanghong 09. Each dive could last eight to 12 hours.

ROV-Mounted Tritex Gauge Tests Corrosion Levels of Sunken Ship
To determine whether there was risk of oil leaking from a sunken World War II ship, the U.K. Ministry of Defence's Salvage and Marine Operations (SANMO) conducted a survey using a Tritex Multigauge 4100 ROV mountable thickness gauge, manufactured by Tritex NDT (Dorchester, England), that was mounted on a Saab Seaeye (Hampshire, England) Falcon ROV.

The gauge inspected the corrosion levels and determined the amount of wastage that has occurred in the hull of the tanker RFA Darkdale and whether there was any risk of the hull leaking any more oil, Tritex said in July. The Multigauge 4100 uses a technology called multiple echo, which means that metal thickness can be measured without removing coatings. The multiple echos are also compared to each other providing error-checked readings from the back wall.

The Darkdale, the first British ship sunk south of the equator, had been sunk to 40 meters depth by a German U-boat. It was hit with four torpedoes while at anchor off Jamestown, St. Helena Island, in October 1941. The hull had been starting to show signs of leaking oil into James Bay.

A team from SANMO was deployed to St. Helena in April to investigate the condition of the ship and to ascertain whether RFA Darkdale is likely to become an environmental hazard.

Following the investigation, Andy Liddell, one of the team members, said, 'The gauge worked and we got readings off the hull. I have to admit to being surprised given the corroded state of the hull.'

Deepwater Search for Earhart Aircraft Begins With ROVs, AUV
Submersible Systems Inc.'s (Patterson, Louisiana) TRV-005 inspection-class ROV and Bluefin Robotics Corp.'s (Quincy, Massachusetts) Bluefin-21 AUV were deployed in July as part of an expedition to search for evidence of Amelia Earheart's lost aircraft. Phoenix International Holdings Inc. (Largo, Maryland) is the expedition's primary contractor.

The search, organized by The International Group for Historic Aircraft Recovery (TIGHAR), is focusing on a reef slope off the west end of Nikumaroro in the southwestern Pacific Republic of Kiribati, where waters can reach depths up to 1,500 meters.

As of July 15, the AUV had run successful missions the previous night, collecting much more data that needed to be processed and plotted. Targets plotted by the AUV were to be ground-truthed with the ROV.

The team reported the coral reef slope was 'a lot more demanding than we knew or even imagined.' Immediately offshore the reef edge in the search area, the reef slope drops in a near vertical cliff hundreds of feet tall. Coral outcroppings on the steep slope tended to snare the ROV tether, forcing the pilot to backtrack to free the snare, the team reported. Further out and deeper, the slope moderates. Except for debris from the SS Norwich City shipwreck, no man-made objects were seen in two 60-foot search swaths from 21 meters down to 365 meters. Flat coral surfaces with right-angle corners resulted in many false alarms.

Operations concluded at the end of July. The team will analyze data and imagery, and reveal its results in August.

Alvin Submersible's New Sphere Passes Pressure Tests
The new titanium personnel sphere for the human-occupied submersible Alvin was successfully pressure tested, said the Woods Hole Oceanographic Institution (WHOI), the vehicle's operator, in June.

The sphere, which holds a pilot and two scientists, is designed to descend to 6,500 meters, which is 2,000 meters deeper than the previous sphere. As the final step in the sphere's construction, the tests validate the sphere design and fabrication and ensure it meets the requirements of the American Bureau of Shipping and the U.S. Navy.

The sphere will be integrated into the Alvin early next year. Over the next several months, WHOI engineers will reassemble the submersible and should begin dock trials in November. Alvin is scheduled to begin certification sea trials in December.

The testing took place at the Northrop Grumman (Falls Church, Virginia) hydrostatic test chamber in Annapolis. The Southwest Research Institute (San Antonio, Texas) managed the design and construction of the titanium sphere as a subcontractor to WHOI.

During the four days of testing, gauges were affixed to the interior and exterior of the sphere to measure strain and 'creep,' the change in the metal from prolonged stress. The sphere was filled with water, placed in a pressurized test tank of water and tested to 8,000 meters—nearly 12,000 pounds per square inch.

The new sphere is 3 inches thick, rather than 2 inches thick. The sphere's interior diameter is 4.6 inches wider than the previous sphere, increasing the interior volume from 144 to 171 cubic feet.

The sphere's construction required more than 34,000 pounds of titanium. Two barrel-shaped titanium ingots were fabricated and then reshaped into two giant hemispheres, which were joined using a special welding technique.


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