14.3 DIVER LOCK-OUT SUBMERSIBLES The third type of underwater platform used by divers is the lock-out submersible (Figures 14-14 through 14-15). Whereas most research submersibles have one or two compartments designed to maintain the crew at a pressure of 1 atmosphere, some submersibles, as well as possessing direct observation and manipulator facilities, possess lock-out capabilities which permit divers to leave the submersible. These vehicles allow divers to be transported to the working site at surface pressure. Numerous viewing ports allow an initial survey to assess working conditions. Lock-out submersibles have a separate chamber capable of being pressurized to ambient pressures so the pilot and other personnel may remain at atmospheric pressure within the submersible while the divers are in the water. Depth and working conditions determine whether the divers use self-contained breathing systems or an umbilical supplied from the submersible. The benefit of a diver lock-out capability is that it reduces diver exposure time, allowing decompression to begin immediately upon return to the vehicle. Some lock-out submersibles have the capability of mating to deck decompression chambers. This allows the diving team to saturate in the chamber on deck, and be transported to the work site via the submersible. The value of the lock-out submersible to the scientist is readily apparent. If required to move, change depths, or remain for extended periods of observation, all are within the immediate resources of the vehicle. If required to go to a depth not readily accessible to a diver in the water, the lockout submersible is an ideal vehicle. Although the diver/scientist normally does not pilot the submersible, he must be familiar with the vehicle's capabilities and operating procedures. A detailed plan must be developed prior to any operation including at least one shallow water excursion so the divers can learn the operating characteristics, the use of all high- and low-pressure systems, as well as decompression and emergency procedures. Lock-out submersibles always have space in the diving chamber for at least two divers. A good practice is to pair up a member of the submerisble's crew with a scientist SO that the crew member can act as a tender when the scientist is in the water. It is preferable to locate the submersible close enough to the dive site so that excursions can all be made using a tethered hookah. This is essential under conditions of high currents (greater than 0.5 knot). Extreme care must be taken when selecting a dive site. Velocity and direction of currents, bottom topography, obstacles on the bottom and maneuverability of the submersible all must be assessed and taken into account prior to any diving. If proper precautions are taken the lock-out submersible can be an excellent tool for the diving scientist. 14.4 FREE FLOODED SUBMERSIBLES While conventional 1 atmosphere and diver lock-ou submersibles require a pressure resistant hull, free flooded submersible (wet sub) can be though of as an underwater convertible. When in use, these vehicles (Figure 14-16) are full of water and the divers breathe using scuba equipment. Th equipment can be open-circuit, semi-closed, closed-circuit systems and may be worn on th back or mounted in the vehicle depending upo the nature of the mission and the design of th submersible. Several configurations of wet subs exist. ! I some, as many as four divers sit one behind other while others are designed to have divers side by-side either sitting or in the prone position. Thes |