Dynamic positioning Dynamic positioning (DP) is a computer-controlled system to automatically maintain a vessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and gyrocompasses, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. Dynamic positioning is a great advantage for saturation diving operations as the risk to the divers and the work area from anchor patterns is reduced, and the vessel can be positioned more quickly.
Saturation system The "saturation system", "saturation complex" or "saturation spread" typically comprises a surface complex made up of a living chamber, transfer chamber and submersible
decompression chamber, which is commonly referred to in
commercial diving and
military diving as the
diving bell,
PTC (personnel transfer capsule) or
SDC (submersible decompression chamber). The system can be permanently installed on the ship or can be capable of being moved from one vessel to another by crane. The entire system is managed from a control room ("van"), where depth, chamber atmosphere and other system parameters are monitored and controlled. The diving bell is the elevator or lift that transfers divers from the system to the work site. Typically, it is mated to the system utilizing a removable clamp and is separated from the system tankage bulkhead by a trunking space, a kind of tunnel, through which the divers transfer to and from the bell. At the completion of work or a mission, the saturation diving team is
decompressed gradually back to
atmospheric pressure by the slow venting of system pressure, at an average of to per day (schedules vary). The process involves only one decompression, thereby avoiding the time-consuming and comparatively risky process of in-water, staged decompression or
sur-D O2 operations normally associated with non-saturation mixed gas diving. More than one living chamber can be linked to the transfer chamber through trunking so that diving teams can be stored at different depths where this is a logistical requirement. 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 divers use
surface supplied umbilical diving equipment, utilizing deep diving
breathing gas, such as helium and oxygen mixtures, stored in large capacity, high pressure
cylinders. The gas supplies are plumbed to the control room, where they are routed to supply the system components. The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water. The bell also is fitted with exterior mounted breathing gas cylinders for emergency use. While in the water the divers will often use a
hot water suit to protect against the cold. The hot water comes from boilers on the surface and is pumped down to the diver via the bell's umbilical and then through the diver's umbilical. The transfer chamber is where the bell is mated to the surface saturation system for transfer under pressure (TUP). It is a wet surface chamber where divers prepare for a dive and strip off and clean their gear after return. Connection to the bell may be overhead, through the bottom hatch of the bell, or lateral, through a side door. The accommodation chambers may be as small as 100 square feet. 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. It is usually possible to isolate each compartment from the others using internal pressure doors.
Diving bell A
closed diving bell, also known as personnel transfer capsule or submersible decompression chamber, is used to transport divers between the workplace and the accommodations chambers. The bell is a cylindrical or spherical pressure vessel with a hatch at the bottom, and may mate with the surface transfer chamber at the bottom hatch or at a side door. Bells are usually designed to carry two or three divers, one of whom, the , stays inside the bell at the bottom and is to the working divers. Each diver is supplied by an umbilical from inside the bell. The bell has a set of high pressure gas storage cylinders mounted on the outside containing on-board reserve breathing gas. The on-board gas and main gas supply are distributed from the bell gas panel, which is controlled by the bellman. The bell may have viewports and external lights. The divers' umbilicals are stored on racks inside the bell during transfer, and are tended by the bellman during the dive. The bell is deployed from a
gantry or
A-frame, also known as a bell
launch and recovery system (LARS), on the vessel or
platform, using a
winch. Deployment may be over the side or through a
moon pool. • The handling system must be able to support the dynamic loads imposed by operating in a range of weather conditions. • It must be able to move the bell through the air/water interface (splash zone) in a controlled way, fast enough to avoid excessive movement caused by wave action. • A
bell cursor may be used to limit lateral motion through and above the splash zone. • It must keep the bell clear of the vessel or platform to prevent impact damage or injury. • It must have sufficient power for fast retrieval of the bell in an emergency, and fine control to facilitate mating of the bell and transfer flange, and to accurately place the bell at the bottom. • It must include a system to move the bell between the mating flange of the transfer chamber and the launch/retrieval position. Diving bells are deployed over the side of the vessel or platform using a gantry or A-frame from which the clump weight and the bell are suspended. On
dive support vessels with in-built saturation systems the bell may be deployed through a
moon pool. The bell handling system is also known as the launch and recovery system (LARS). This is also used to move the bell from the position where it is locked on to the chamber system into the water, lower it to the working depth and hold it at that depth without excessive movement, for which heave compensation equipment may be fitted to the winch, and recover it to the chamber system. The system used to transfer the bell on deck may be a deck trolley system, an overhead gantry or a swinging A-frame. The system must constrain movement of the supported bell sufficiently to allow accurate location on the chamber trunking even in bad weather. A bell cursor may be used to control movement through and above the splash zone, and heave compensation gear may be used to limit vertical movement when in the water and clear of the cursor, particularly at working depth when the diver may be locked out and the bell is open to ambient pressure. gear may be useful to place the bell closer to the worksite if the ship cannot safely approach it to a convenient distance
Moon pool 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. ==Diving from a DSV==