We will use the terms manned submersible and deep submersible interchangeably. "Manned submersible" has recently been determined to be politically incorrect with the suggested substitute being "human occupied submersible vehicle". We'll use "deep submersible" for the sake of simplicity.
Where are deep submersibles used today?
Deep submersibles are used primarily in the area of marine science research where there are approximately 40 vehicles world wide attributed to that purpose. Some are laid up and others get little use. However, most marine scientists feel that there is no substitute for "in situ" direct observation and they refuse to accept remote methods of observation (e.g. ROVs).
Has deep submersible use declined? If so, why?
Deep submersibles were used extensively by the offshore oil companies in support of survey, drilling and production operations. They were used as an adjunct to extend the capabilities of shallow water and saturation dive teams. Over time, their use became supplanted by remotely operated vehicles (ROVs) which have made continual gains in sophistication and capability. Compared to deep submersibles, ROVs are less costly to operate, maintain and insure. Today, there are virtually no deep submersibles in use in the commercial offshore business.
Just what is an ROV?
An ROV is a tethered remotely operated vehicle where power and control capability is provided through an umbilical cable. The vehicle is controlled by an operator from a control van using joysticks, video monitors and various instrument readouts. ROVs range in size from small portable units that cost $10,000 or less, to large, high horsepower behemoths costing millions of dollars. Depending on the task at hand, ROVs are equipped with a myriad of devices from sensitive spatially correspondent manipulators to special jetting and trenching attachments.
What about deep submersibles for personal use?
The problem with deep submersibles is their weight. Imagine, if you will, trying to push a large beach ball completely underwater. It's a struggle. In order to get that beach ball to sink and be neutrally buoyant, you have to weigh it down significantly. In fact, according to Archimede's Principal the weight must be equivalent to the volume of water the beach ball displaces, and water is quite heavy. It's the same thing with a submersible. Depending on the depth requirement the vehicle will be constructed of medium to high tensile steel, but in most cases lead weights will have to be added to achieve neutral buoyancy. A typical contemporary two passenger submersible will weigh a minimum of about 3 tons. A three passenger unit about 4.5 tons, minimum. If you need more interior space for equipment, the weight increases rapidly such that older 3-passenger commercial subs are likely to weigh in at 7 - 9 tons.
It is very difficult to transport a deep submersible on a trailer behind a conventional car or truck. Once at the water, they must be launched from a crane or travel lift, because most designs draw too much water to be launched from a boat ramp. Once in the water they must be used in close proximity to the launching point because being battery powered they have very limited range and endurance. And, because of their weight and cross sectional area, they tow like bricks. A maximum towing speed is generally 4 knots.
However, U.S. Submarines has developed a unique submersible that can be used effectively as a personal vehicle. Our Triton 650 takes advantage of a unique catamaran style configuration to reduce draft, and the low volume approach minimizes weight while the transparent pressure hull provides exceptional viewing.
What about operating deep submersibles from a yacht or ship?
Deep submersibles used for marine science research have virtually always been launched from and retrieved to a surface support ship. But, because of the weights involved the ships have been large, typically at least 35 meters in length, and the launch and recovery equipment has been specialized, expensive and heavy. These launch and recovery systems themselves can easily cost over $350,000. They are usually "man rated" by the American Bureau of Shipping so that scientists can enter and exit the submersible on the deck of the ship. Launching a 5 to 25 ton submersible from and recovering it to a support ship is no trivial task, particularly in marginal sea conditions where lateral and snatch loads can be greatly increased due to the motion of the ship and the submersible.
However, if the launch and recovery requirement is taken into consideration early in the yacht construction process and matched to a specialized submersible the systems can be well integrated. But, for this to happen the submersible must be designed to be entered and exited while in the water because the construction requirements for a man rated launch and recovery system are much more pronounced. At U.S. Submarines we worked with the world leader in launch and recovery systems and developed a unit that was stern mounted and would launch, recover and carry our 7 ton Discovery 1000. The submarine and the launch and recovery unit could be easily removed from the deck of the yacht and placed in a 40 foot container and shipped anywhere in the world. Our small, lightweight Triton 650 can be launched from most large yacht davit systems with minimal modification.
What about the cost of deep submersible operations?
You can rent time on a research sub from one of several marine science research groups. Generally, the cost will be about $5,000 per day for the submersible and crew and about $12,500 per day for the support ship and crew. The high cost of operations is one significant contributingfactor to the decrease in deep submersible utilization.
In a luxury yacht environment the situation is much different. A contemporary purpose-built deep submersible like our $640,000 Triton 650 is a light weight, low maintenance design that minimizes the expense and difficulty of launch and recovery and the operating costs are virtually unnoticeable in the yacht's overall budget. One crew member can be trained to maintain the submersible and the owner or crew can be trained to pilot the submersible in a relatively short period of time.
Some older deep submersibles are listed for sale. Are they viable to operate?
There are a large number of older deep submersibles that are advertised for sale. Generally, they are large and heavy and require significant maintenance due to their old and outmoded systems. Many are not stable on the surface and so must have man-rated launch and recovery systems that are very expensive. To be used in practical applications, these submersibles require large support ships and any money saved by buying an older heavy submersible will be spent several times over in the support ship and launch and recovery system requirement. If you have a commercial or scientific task and substantial financial resources to pay a highly specialized trained crew for the sub and a large support vessel, then an older submersible may make sense. Otherwise, these older deep submersibles make good static displays and museum pieces.
Are there any conditions where the use of older submersibles might be practical?
Yes, there are two possibilities that come to mind. If you are fortunate enough to live immediately adjacent to an operating area where you can keep the sub on your dock, bulkhead or marine railway and your principal operating location is within 0.5 kilometer, an older submersible may make sense. If you are willing to tow the sub at speeds of less than 3 knots you can expand the operating area in that manner. However, you must choose a submersible that has good surface stability and adequate freeboard so that you can easily enter and exit the vehicle while at sea, and you should be aware that your comparative maintenance requirement will be relatively high.
A second possibility is to purchase a complete integrated system. For instance, on a few occasions deep submersibles have been built with dedicated self powered catamaran style surface support vessels that have integrated launch and recovery and support equipment (e.g. generators, battery chargers, air compressor, spares storage) but are small enough to be cost effective to operate within a limited area from base. The Bruker Mermaid IV is one such system that is available for about $600,000 for the catamaran and the submersible. A catamaran has also been built for one of the SM-100/3 submersibles.
What sort of contemporary deep submersibles have been built in recent years?
In 1987 a Finnish company, Rauma Oceanics, built the Mir 1 & Mir 2 for the Russian Academy of Sciences. These are the submersible that were used to film the Titanic. The Mirs cost about $25 million each and have a 6,000 meter depth rating. Just before the Mirs were delivered the Japanese completed the $60 + million Shinkai 6500, which with a depth rating of 6500 meters is the deepest diving manned submersible today.
A few years ago an American company built two DR1002s which have spherical transparent pressure hulls and a depth rating of 1000 meters. These two submersibles cost $1.7 million each and are used by Canal Plus, the French television group.
Last year a French company completed the second Remora, a 2-passenger, 600 meter capable submersible that also has a transparent spherical acrylic pressure hull. The sub was delivered to the Greek Dept. of Antiquities in 1999.
What will the future be like for manned submersibles?
This is a subject of interesting speculation. There has not been much activity in the deep submersible field over the last several years. Technical advances in the use of acrylic have provided a preferred alternative for construction of these vehicles. The Remora and the DR1002 following in the footsteps of the earlier Johnson SeaLinks have proven the superiority of the acrylic hull for depths to 1000 meters. Interestingly enough, they have also proven cost effective. Building a conventional deep submersible with 1000 meter depth rating like Pisces II for example would cost significantly more than the $1.7 million for the DR1002. So, there is an economic advantage, yet in most situations manned submersible utilization fails the basic cost benefit economic test, in large part because of the expense of the surface support ship.
It is possible that the advent of usable air independent propulsion systems (e.g. closed cycle diesel, closed cycle Stirling, PEM fuel cells, etc.) coupled with diesel electric submarine autonomy as demonstrated by our Nomad or Seattle designs could provide a cost effective and capable alternative. In this case, small to mid size submarines can transit to a dive site while on the surface and then spend days operating underwater before returning to the surface for the trip home. AIP capability can dramatically expand the undersea range and endurance and the diesel electric capability obviates the need for a surface support ship thus cutting the overall system operating costs by half.
Otherwise there will be some call for replacements for conventional deep submersibles used for marine science research that have aged to the point that they are no longer safe or cost effective. And, ROVs used in the offshore oil industry run up against limitations at depths of 3500 meters or more and new manned submersibles may prove the only viable substitute.