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An umbilical cable or umbilical is a cable and/or hose that supplies required consumables to an apparatus, like a rocket, or to a person, such as a diver or astronaut. It is named by analogy with an umbilical cord. An umbilical can, for example, supply air and power to a pressure suit or fluid power, electrical power and fiber optics to subsea equipment and divers.
Umbilical connections are also used between rocket stages, and between the rocket and its spacecraft payload; these umbilicals are disconnected as stages are disconnected and discarded.
For shallow water surface supply air diving, the diver's umbilical is typically a 3-part umbilical comprising a bore breathing gas hose, bore pneumofathometer ("pneumo") hose, and diver communications cable, which usually also serves as a lifeline strength member. The pneumo hose is open at the diver's end and the other end is connected to a pressure gauge on the surface gas panel, where the supervisor can use it to measure the diver's depth in the water at any time. This is done by measuring pressure of the air in the pneumo hose after a thin stream of bubbles has been emitted from the open end which ensures that the hose has been purged of water so that the internal gas pressure is effectively constant and equal to the ambient pressure at the open end. The umbilical serves as a lifeline and must be capable of lifting the diver out of the water safely. Maximum permitted service life for rubber breathing air hoses is 12 years, but synthetic (unfilled polyurethane elastomer) lined hoses may be used without time limit while in good condition as long as they pass inspection and testing. Hot water supply hoses are more likely to be rubber lined, and polyurethane external sheathing is common for all umbilical hoses and cables.
A typical 4-part diver umbilical will also have a bore hot water supply hose for the diver's exposure suit. A 5-part diver umbilical will also include a video cable to allow the surface controller to see the video picture transmitted to the surface from the diver's hat camera (video camera mounted on the helmet, facing forward, with a field of vision similar to that of the diver).
An excursion umbilical from a wet bell would be similar in construction, but shorter than an umbilical supplied directly from the surface for similar work. For saturation diving from a closed bell, a diver excursion umbilical includes a breathing gas supply hose, gas reclaim hose, hot water hose, pneumofathometer hose, voice communications and lifeline cable, video cable and helmet light power cable.
Early diver umbilicals were simply the individual components bundled together and taped every metre or so with duct tape. These bundles tend to distort and produce kinks in the components caused by bending (particularly dangerous if the kink is in the divers gas supply hose), and require frequent maintenance. More recent umbilicals usually comprise all the components laid together like a twisted rope, so that there is little chance of a kink, no separate lifeline component is required, and no tape is required to hold the umbilical together. An additional component such as a video cable for a diver's camera, or a hat light cable, can be added by manually wrapping this additional component into the lay of the existing cabled umbilical. When there is risk of the umbilical cable being damaged by scratching on rock, coral or wreckage, the umbilical bundle may be over-braided with a polypropylene braid cover, or a velcro fastened textile cover.
The length of the diver's umbilical will depend on the operational parameters. As a general rule a short umbilical is cheaper and more manageable than a longer one, and provided that it is long enough, shorter is generally safer. The standby diver or bellman's umbilical should generally be about longer than that of the working diver to allow easy access to the diver in an emergency. A common length established by custom and experience is for a closed bell diver's umbilical, but this may be varied when circumstances require. For surface oriented work it is often necessary to use a longer umbilical. Deployable length may be controlled by tying off the umbilical at the rack to reduce the risk of the diver approaching known hazards too closely. The IMCA specification is minimum distance from a hazard.
The factors that influence length of a surface oriented umbilical include:
Diver umbilicals may be negatively buoyant, neutral or positive, depending on the operational requirements. It is a common practice to mark them at length intervals using colour coded tape.
A closed-bell handling system includes a bell umbilical handling system, which deploys, recovers and stores the umbilical.
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