Manned submersibles are vertical probes where mission times rarely exceed 12 to 14 hours and require mother ships on site to tend them and their crews. There are only four manned submersibles in the world that can dive to a test depth of 20,000 feet, or slightly deeper. Two are Russian, with France and Japan each having one. Japan's Shinkai 6500 is currently the world's deepest diver at 21,300 feet.
This exclusive club will be soon joined by the Chinese who are completing a 23,000-foot-capable manned vehicle. It should be in service by 2009-10. The titanium pressure hull was built in St. Petersburg, Russia, while other construction work and assembly are being done at Harbin, China.
The United States no longer has this capability even though it was the founding member of the 20,000-foot club. When the Bathyscaph Trieste II was retired in the early 1980s, the Navy's Sea Cliff was converted from a 6,500-foot to a 20,000-foot vehicle. Then after the Sea Cliff's retirement in 1998 it was given to the Woods Hole Oceanographic Institution, which decided not to return it to service.
Instead, Woods Hole is working to replace its 40-year-old Alvin, capable of diving to 14,700-feet and having made more than 4,400 dives. In August 2007, the institution awarded a $2.8 million contract to Lockheed Martin for initial design of the new vehicle with a depth capability of 21,325 feet. If there are no technical and funding delays, the sub could go into service by the end of this decade. The U.S. National Science Foundation is funding the replacement at an estimated cost of $25 million.
While the ocean's maximum depth is nearly 36,000 feet, there are no firm plans in any country to develop a manned submersible for this depth. All of the present and planned manned vehicles are clustered around a 20,000- to 23,000-foot test depth, which provides access to nearly 98 percent of the sea floor.
An interesting development over the past two decades is the use of manned deep-diving submersibles in tourism with about 50 shallow-diving (150-foot maximum) tourist submarines in service since 1985. Each carries 40-50 people on a one-hour dive. To date, these vehicles have carried more than 4 million passengers without any serious incidents.
"Adventure Diving," a new branch of seagoing tourism to depths down to 15,200 feet, is the next step for the extreme tourist with a fat wallet. These operations are not cheap, and available submersible assets are very limited. At present, only the two Russian Mir submersibles are doing this work. The other manned subs in the 20,000-foot club do not have room for more than a single paying passenger. With the mother ship plus sub charter rates running to more than $55,000 per diving day, a ticket on a one-tourist-only sub would be a huge expense. But with four tourists per day using two Mirs, the per-person price is significantly reduced. For example, a 12-hour dive to the Titanic costs about $35,000.
But this access could be further restricted as the Russian government regenerates its economy and increases investment in its scientific community. Last August, as part of Russia's contribution to the International Polar Year, the two Mirs made pioneering first dives to the genuine North Pole at 14,400 feet. In the future, they and their mother ship, Akademik Keldysh, will be less available for adventure diving.
Several manned submersibles can dive in the 2,000- to 3,300-foot range and more, though limited, adventure diving will continue to be offered. Sadly, future tourist divers will not have the bragging rights of having lunch on board the Titanic (at 12,200 feet, halfway through the 12-hour dives, the Mirs would land on the bridge of the Titanic for a lunch break). A similar experience was to have lunch on board the World War II German battleship Bismarck at 15,200 feet.
The use of manned submersibles for research and commercial purposes will continue. A wide variety of subs are available or are under construction. In addition, a range of robotic submersibles are available in which the presence of man is not needed.
While users and missions of manned submersible platforms may change over time, the basics of "being there" remain unchanged. It is hard to beat having the trained mind and eye present at the ocean work site. Hopefully test depths for a few of the vehicles will be much deeper than at present.