Diving support vessel
Basic requirements are the ability to keep station accurately and reliably throughout a diving operation, often in close proximity to drilling or production platforms, for positioning to degrade slowly enough in deteriorating conditions to recover divers without excessive risk, and to carry the necessary support equipment for the mode of diving to be used.
[1] Basic requirements are the ability to keep station accurately and reliably throughout a diving operation, often in close proximity to drilling or production platforms, for positioning to degrade slowly enough in deteriorating conditions to recover divers without excessive risk, and to carry the necessary support equipment for the mode of diving to be used.
Until that point, most diving operations were from mobile oil drilling platforms, pipe-lay, or crane barges.
The semi-submersible fleet, the Uncle John and similar, have proven to be too expensive to maintain and too slow to move between fields.
However, driven by high oil prices since 2004, the market for subsea developments in the North Sea has grown significantly.
They may carry 80 to 150 project personnel on board, including divers, diving supervisors and superintendents, dive technicians, life support technicians and supervisors, ROV pilots, ROV superintendents, survey team, clients personnel, etc.
In expanding the utility of the vessel, these vessels provide, in addition to the usual domestic facilities, specialised diving mixed gas compressors and reclaim systems, gas storage and blending facilities, and saturation diving accommodation systems where the divers live under compression.
An extra chamber can be fitted to transfer personnel into and out of the system while under pressure and to treat divers for decompression sickness if this should be necessary.
The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water.
It is a wet surface chamber where divers prepare for a dive and strip off and clean their gear after return.
[7] This part is generally made of multiple compartments, including living, sanitation, and rest facilities, each a separate unit, joined by short lengths of cylindrical trunking.
[8] The divers' umbilicals are stored on racks inside the bell during transfer, and are tended by the bellman during the dive.
The system must constrain movement of the supported bell sufficiently to allow accurate location on the chamber trunking even in bad weather.
[9] Cross-hauling gear may be useful to place the bell closer to the worksite if the ship cannot safely approach it to a convenient distance A moon pool is an opening in the base of the hull, giving access to the water below, which allows divers, diving bells, remotely operated underwater vehicles or other equipment to enter or leave the water easily and in a relatively protected environment.
Standard practices for diving from a DSV include the use of stages, wet and dry bells to transport the diver through the interface between air and water, to avoid hazards, and for decompression.
Additional underwater tending points may be needed, and one of the methods used is for the diver to pass through a heavy hoop, which may be deployed by crane to a specific position on or near the bottom, The reach of the umbilical beyond each tending point should not allow the diver close approach to known high risk hazards.
