Diving Support Vessel (DSV) is designed for diving operations carried out below and around oil production platforms and related installations in open waters. These vessels are used for underwater repair, inspection, construction works, well intervention and etc. Most of the modern DSV vessels designed for efficient diving operations in harsh environments.
DSV 'Constructor' (Boskalis)
As a rule, DSV vessels are equipped with Dynamic Positioning (DP2 or DP3 systems) and Saturation diving systems.
Most of these vessels are equipped with heavy lift cranes with deep water capability and are fitted out to support work class remotely operated vehicles (ROVs). For these purposes there is a special ROV hangar and ROV control room, which is fully integrated in the vessel.
Different diving support purposes require varying vessel lengths and the integration of different diving saturation systems. Vessel lengths ranging from 94 to 132 meters allow for the integration of diving systems with a capacity of six, 12 or 18 divers. The systems have a depth rating of 100, 200 and 300 meters of seawater respectively, and can be equipped with a single- or twin-bell launch and recovery system each through a dedicated diving moon pool. The saturation diving system enforces the presence of combination of certain important gases like helium and oxygen for the diver.
Saturation diving system
Saturation diving system - For diving operations below 50m, a mixture of helium and oxygen (heliox) is required to eliminate the narcotic effect of nitrogen under pressure. For extended diving operations at depth, saturation diving is the preferred approach. A saturation system would be installed within the ship. A diving bell would transport the divers between the saturation system and the work site lowered through a 'moon pool' in the bottom of the ship, usually with a support structure 'cursor' to support the diving bell through the turbulent waters near the surface. There are a number of support systems for the saturation system on a Diving Support Vessel, usually including a Remotely Operated Vehicle ROV and heavy lifting equipment.
Full Saturation Diving System Assembly with vessel (Image: www.smp-ltd.com)
Diving bell is a sealed chamber, which may be used for mixed gas bounce diving and for saturation diving. This form of bell locks on and off the chamber where the divers live, by way of a closed door sealing the divers in at pressure. Once on the surface, the bell is mated with the chamber system and the space in between is pressurized to enable to divers to make a seal and transfer through to the chamber which is at the same pressure. In saturation diving the bell is merely the ride to and from the job, and the chamber is the living quarters. If the dive is relatively short (a bounce dive), decompression can be done in the bell in exactly the same way it would be done in the chamber.
Remotely operated vehicles (ROVs) are robot submarines that are tethered to a ship, where operators ("pilots") control their movement and actions.
Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle’s capabilities. These may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, light penetration and temperature.
ROV HerculesР ’ on board the E/VNautilus Photo: oceanexplorer.noaa.gov
ROVs can vary in size from small vehicles with TVs for simple observation up to complex work systems, which can have several dexterous manipulators, TV's, video cameras, tools and other equipment. The mechanism of the top hat handling system, which contains deployable neutrally buoyant cable for local excursions. Such handling techniques allow the heavy umbilical to remain vertical in the water column while the ROV maneuvers with the smaller cable, free of the surface dynamics, which in many cases, can pull the ROV from its work station.