by Brian Leshak
On May 11, 2012, a few miles off Panama City, Fla., a diving bell containing three divers from the U.S. Navy Experimental Diving Unit descended slowly and steadily through the darkness of the Gulf of Mexico far below the depth that sunlight can reach.
Increasing water pressure compressed the air inside the diving bell, which was open to the sea, so more air was released into the bell to keep the volume of air constant and prevent seawater from entering. As the increasing pressure raised the saturation point of the diver’s bodies, their tissue absorbed additional gases from the air. Therefore, the mixture of gases within the capsule’s air required alteration during the descent to maintain the optimal mix for working at depth.
Finally, the divers reached their goal, a depth that no U.S. Navy diver had attained in an open diving bell since the 1970s. One by one, they left the confines of the bell and took up positions on a diving stage already positioned at the target depth. “We made it!” one of them exclaimed over a voice link to their support team on the surface far above. The last time U.S. Navy personnel had reached comparable depth in an open bell was in 1975, when a two-man team performed a saturation dive to 1,148 feet with the MK 1 Deep Diving System.
Another three-man team from the Experimental Diving Unit also completed a dive to the target depth. One of the teams conducted excursions from the bell at 1,001 “feet of salt water” (FSW), and the other at 1,004 FSW. These successful dives enabled NAVSEA’s Supervisor of Salvage and Diving (SUPSALV) to certify the Navy’s new Saturation (SAT) Fly Away Diving System (FADS) to 1,000 FSW, reestablishing an important capability the Navy has not had for decades.
Upon completing their dives, the teams returned to the diving bell, which was raised to the surface so the divers could transfer to the deck decompression chamber (DDC). The divers spent the next nine days in the DDC, slowly decompressing from the demanding pressure of 445 pounds per square inch—the pressure found at depths of 1,000 FSW—back to the normal atmospheric pressure of the earth’s surface.
The Navy developed saturation diving in the 1960s as a safe way to extend bottom time for deep ocean salvage and submarine rescue, as well as recovery at depths up to 1,000 feet. Once divers reach the saturation point for the depth at which they will be working, it is much more efficient for them to continue at that pressure until the job is done rather than interrupt the work for days of decompressing.
In May 2012, a dive bell descends past 300 FSW on its way to
making a historic 1000 FSW manned open ocean bell excursion
by three U.S. Navy Saturation Divers in the Gulf of Mexico.
(Photo by NAVSEA SUPSALV ROV—Phoenix International)
Saturated diving requires a system that can keep divers under pressure when they return to the surface for food and rest. Therefore, the diving bell must have the capability to close off from the sea and maintain its internal pressure as it ascends. Once on the surface, the diving bell must be able to transfer the divers to a decompression chamber where they can live under pressure while not working at depth, and then eventually undergo the protracted decompression process after completing their work.
From the 1980s to the mid-1990s, the Navy had no such capability. With most of its afloat diving and salvage platforms having been decommissioned, including those that supported saturation diving, the Navy was forced to rely on commercial saturation diving systems to the extent it conducted such operations at all.
The process of bringing an approved open-water diving system back to the Navy began in 2003, when OPNAV’s Submarine Warfare Division (N87) proposed an acquisition program for SAT FADS and gained approval from the Chief of Naval Operations. “Bringing SAT FADS back to the Navy was essential to support the full range of Navy salvage and recovery operations,” said Michael Dean, SUPSALV’s deputy director. “Those operations include crisis response from emergent causalities, as well as planned response in and around the world’s littorals and continental shelves.”
“SAT FADS provides the ability for Navy divers to work underwater longer, at greater depths, while avoiding large in-water decompression penalties,” Dean noted. “The saturation diving technique allows divers to postpone the lengthy decompression process until the completion of the mission when they can be safely decompressed in an on-deck recompression chamber.”
SAT FADS measures just 40 feet by 80 feet. It includes the deck decompression chamber—which serves as pressurized living quarters for the divers during an operation—the manned dive bell, a handling system, a command and control center, two auxiliary support equipment containers, and storage racks for bulk helium and oxygen. The entire system is air-transportable, so it can be rapidly transported anywhere in the world and loaded onto any suitable vessel of opportunity to conduct diving operations.
SAT FADS is designed to support six divers working on the ocean floor at a depth of 1,000 feet for up to 21 days, with an additional nine days of decompression. This capability makes it possible to support deep aircraft and ship recovery, or salvage operations. Three divers working in a team can work up to eight hours a day from SAT FADS during an operation, with another three-man team aboard the unit able to rotate in and continue work with minimal interruption until the job is completed.
The new system surpasses the capability that was provided by the Navy’s last saturated diving platforms, the two decommissioned Pigeon-class submarine rescue vessels. These two dedicated vessels, decommissioned over a decade ago, allowed divers to operate only to a maximum depth of 850 feet, as compared to 1,000 feet for the new system. Air-portability makes the new system far more mobile and responsive. SAT FADS provides all this capability for a fraction of the total ownership cost of any previous ship-based saturated diving system.
“This system increases the Navy’s salvage and diving capabilities, allowing us to put U.S. Navy saturation divers to greater ocean depths than previously attainable,” said Paul McMurtrie, a retired Navy master diver now serving as the SAT FADS program manager. “This new asset will greatly increase our manned diving capabilities, as well as provide a one-of-a-kind training asset for future Navy saturation divers.”
“Having SAT FADS back in the Navy is very beneficial to the Navy diving community,” said Cmdr. Mark Matthews, SUPSALV’s director. “These are exciting times for the diving community, as we no longer have to wait for commercially available SAT systems in times of need, [and] we also can begin training other divers on our newly approved system.”
Brian Leshak is a Public Affairs Officer for the Naval Sea Systems Command.
Photo at top: Jonathan Gibson; Naval Surface Warfare Center Panama City Division