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DeepWorker Deployment and Recovery
Launch and recovery procedures are potentially the most hazardous aspect of any manned submersible operations. During launch and recovery, the lives of the pilot and the ship’s crew are at stake. Should anything go wrong, serious or fatal injuries are possible. That is why launch and recovery systems are carefully maintained and procedures are strictly followed by trained personnel. Background The launch and recovery of a submersible define the beginning and end of each dive. The launch process begins with satisfactory completion of the pre-dive checklist, and includes evaluation of weather and sea conditions, the ship’s arrival at the designated “station” where the launch will occur, and manning of the launch equipment. Recovery begins when the submersible surfaces, includes “hook and lift” operations to bring it up, and ends when it is safely on deck. Chain of Command At any one time during launch and recovery, 10-15 people are manning stations or performing tasks. To ensure the safety and efficiency of the operation, there is a clear and authoritative chain of command. The Dive Supervisor provides a single point of control for the activities occurring both on the ship and in the sub. All personnel involved in the operation receive commands directly from the Dive Supervisor, including the ship’s Officer of the Deck (OOD), who is on the bridge driving the ship. The Dive Supervisor is in direct VHF radio communication with the bridge, the tracking technician, the pilot, the chief boatswain, and the swimmer. As soon as the pilot is in the submersible and the hatch is closed, the Dive Supervisor takes command of the operation and maintains control until the submersible is safely back on deck. The dive supervisor then notifies the ship to resume normal operations. When the sub is unhooked from all launch and recovery lines and equipment, and is approved by the dive supervisor, the pilot assumes control of the sub, and his actions are coordinated with those of the ship. Considerations for Launch and Recovery Several factors must be considered before proceeding with launch and recovery operations. Failure to make each and every observation can jeopardize the lives of the submersible pilot(s), passenger(s) and crew members. It is the responsibility of the Commanding Officer (C.O.) and Dive Supervisor to concur on acceptable conditions and determine if dive operations can be conducted. Many combinations of wind and sea conditions may define the acceptable window for launch and recovery. There are no preset thresholds of velocity, height, or direction of wind or sea conditions that, by themselves, can shut down a launch or recovery opportunity. The combination of all the following variables must be considered: The trend of wind speed for the last three hours and current observations; surface current velocity and direction for the last three hours; wave height, wave period and wave direction for the last three hours; primary swell direction; secondary swell direction; visibility: fog, rain, cloud cover; thunder, lightning, squalls; other vessel traffic, and proximity to land or other obstructions. In preparation for recovery, the C.O. and Dive Supervisor will continue to assess conditions throughout the period of the dive. These conditions include weather, impending and/or hazardous vessel traffic, and emergency incidents on the ship or sub. Effects of Vessel Configuration on Launch and Recovery
Three main areas of vessel configuration affect launch and recovery operations. These are the propulsion system, the type of lift device and lift device location. The characteristics of vessels used to launch submersibles vary from ship to ship; some are equipped with bow thrusters, which significantly improve maneuverability, as do twin screws or propellers. Ships with only one screw (propeller) and no bow thrusters are less maneuverable. Ships with controllable pitch screws (the angle of the propeller blades can be changed) have the advantage of better speed control. However, when a ship with controllable pitch screws is at “all-stop” (a phrase meaning that the ship is not moving ahead or backward), the screws continue to turn and present two disadvantages: (1) significant acoustic noise is generated, interfering with both the tracking and underwater communications systems, and (2) a constant turning screw can be hazardous when a swimmer is in the water and lines are in the water in back of the ship. Ships equipped with a combination of Z-drive or similar propulsion system and an omni-thruster provide the best maneuverability of all. Lift Types and Locations There are three primary lift types used in manned submersible operations: A-frames, articulated cranes, and nonarticulated cranes. The positions of these lifts on the vessel greatly affect their useability for launch-and-recovery operations. Stern A-Frame The stern mounted A-frame is the preferred launch-and-recovery method for many submersibles, since the effect of ship roll (side-to-side movement) is reduced and the submersible is brought straight aboard. Horizontal rotation of the submersible is prevented or lessened by steadying lines (often called tag lines) attached to the submersible. These tag lines usually run to tugger winches or cleats on the port and starboard sides and are handled by deck personnel.
Stern Crane The stern mounted crane retains the advantage of reducing the effects of ship roll; however, since the stern crane sometimes swings in an arc and at some point is athwart (crossing the line of the ship), it has some disadvantages. When using a stern crane, tag lines, like those used for stern A-frame configurations, are used to steady the submersible while it is suspended. Side Cranes: Articulated and Nonarticulated A side-mounted crane can be severely affected by roll motion, making hook-up to certain submersibles very difficult. One advantage of the side mount, however, is the reduced effects of pitch (the alternative dipping of the bow and stern). Certain long-bodied or linear-shaped submersibles, such as the Delta submersible, prefer side-crane launch and recovery because it allows the submersible to be held flat against the ship, stabilizing it and keeping it from swinging freely as the ship pitches or rolls. An articulated crane has a knuckle, similar in function to a knuckle on a hand. It is a bending point that allows increased flexibility and movement. A nonarticulated crane does not have a knuckle. Articulated cranes are generally considered to be better than nonarticulated cranes since they can usually be brought closer to the submersible. This reduces the amount of lifting line and any subsequent pendulum effect while the submersible is suspended. Lines During launch and recovery, several types of lines serve different purposes. The primary line critical to getting the submersible into and out of the water is called the lift line. The lift line runs through the a-frame or crane and connects to a winch on deck. The winch is controlled by a crew member under the direction of the Dive Supervisor. Another critical line used to tow the submersible is called the tow line. Mostly used for stern launches and recoveries, the tow line keeps the submersible connected to the ship at a safe distance so that it does not come in contact with the ship during final preparations to hook it up or release it.
The tag lines are stabilizing lines attached to the sides or ends of the submersible that prevent it from swinging in mid-air while being raised or lowered. Tag lines are often handled by crew members on deck, but are sometimes controlled by special winches mounted to the ship deck, called tugger winches. When tugger winches are not used, the crew member must hold the tag line tight over a cleat to keep the submersible from swinging side to side and possibly hitting the ship or other deck equipment. Other Equipment
The operation of any combination of lift device and location can be greatly improved when a constant tension winch is installed. The constant tension winch eliminates the problem of the lift line alternately going slack and then tightening when the ship is pitching. This reduces the amount of stress on the equipment and helps to protect the swimmer who is attempting to hook or unhook the submersible. Swimmers The swimmer is a critical part of launch and recovery for many submersible operations. The swimmer is responsible for connecting and disconnecting the submersible from the lifting and handling equipment and lines when the submersible is in the water. During launch, the swimmer disconnects all lines, ensures all external submersible equipment is set and cleared of all lines, and attaches any additional gear to the submersible. During recovery, the swimmer prepares the submersible and equipment, often attaching special protective covers to expensive scientific equipment or cameras, and attaches all of the lift and tag lines. The use of the swimmer however, is minimized by any means possible because the longer the swimmer is in the water, the greater the chances of personal injury. |
