Launching and recovery of a submersible from a surface vessel are restricted to periods of relatively calm weather conditions. A study has been made of using a submarine for this purpose in order to create an all-weather system. This paper describes such a Submarine Support Vessel (SSV), its performance and its construction costs. The SSV can handle submersibles, with divers, of up to about 50 tons.
The need for submersibles in the off-shore industry is increasing. Whereas they were formerly used mainly for research, they are becoming deeply involved in the industrial process for inspection, service and maintenance purposes. These tasks can be performed either from within the submersible or by using it as a transportation means for transferring personnel and equipment in docking operation or in diver lockout operations.
The submersible has a limited autonomy and requires a support ship,' from which the submersible is being launched and recovered. At present these operations can be performed in Sea States 4 or 5 at most. In many waters this will considerably restrict the availability of the system, for example in the North Sea.
There may be various solutions to improve the availability such as increasing the size of the support ships, using catamaran or semisubmersible types, or by using suspended docking platforms; all of the latter, however, only transfers the problem without solving it.
The solution is to turn the support vessel into a submarine and to perform launching and recovery completely submerged. The operations can then be comfortably performed without any crane arrangement and independent of the weather conditions.
At Kockums Shipyard we have carried out a study of a Submarine Support Vessel intended to support a 50 tons submersible. The reason why we chose this specific submersible is that we have developed in cooperation with the French company COMEX such a submersible as a Submarine Rescue Vehicle for the Royal Swedish Navy. This vehicle is now under construction at our shipyard under a Navy contract of about $ 3.5 million. In a civilian version it would have a diving depth of 460 m (1,500 feet), a complete diver lockout system for 2 divers plus a payload of about 3,000 kgs.
The Submarine Support Vessel carries the submersible in a sheltered compartment on top of the pressure hull. Launching and recovery operations are always performed with the SSV submerged at any depth down to 125 m (400 feet). The advantages are that calm water conditions can be obtained, thus achieving an all-weather system, and also that the operations will be performed without using heavy cranes.
The Submarine Support Vessel will leave the harbour carrying the submersible in its hangar. The voyage to the operation area will be undertaken either surfaced at 12 knots or snorting at 10 knots. In the working area the SSV will either remain on the surface of dive to a snorting position depending upon the weather conditions, except when launching and recovering the submersible, which will always be performed totally submerged.