Construction and operation of a two-place diver's sled

tag:blogger.com,1999:blog-4961986629945631946.post-47795636189476987862008-03-14T05:41:00.000-07:002008-03-14T05:53:40.263-07:00Construction and operation of a two-place diver's sledFisheries gear researchers have employed scuba diver-operated sleds to evaluate towed fishing systems since the early 1950's. One of the earliest sled designs was a converted Stokes litter in which two divers sat tandem with the forward diver operating the diving controls (Sand, 1956). The litter was relatively easy to maneuver and provided a comfortable platform for observing operational fishing gear. However, the use of underwater photographic equipment to document gear performance was difficult due to the limited mobility of the observer-cameraman. A new two-place diver's sled, designed specifically for underwater cinematography, was introduced in the late 1950's (Hold, 1960). This sled allowed the divers to lie side-by-side which greatly reduced water resistance. The sled pilot occupied the port position, and the observer-cameraman, facing either forward or aft, occupied the starboard position. This design offered two advantages over the converted Stokes litter: 1) It was more maneuverable due to the location of its towing point and 2) it facilitated the use of underwater photographic equipment. Disadvantages of this steel sled were that it was heavy, subject to corrosion, and accessory flotation tanks were necessary for positive buoyancy. The weight and corrosion problems were solved in the late 1960's by replacing the steel frame and wooden control surfaces with aluminum (1). The lighter weight and reduced accessory flotation requirements made the aluminum two-place diver's sled more maneuverable than the steel sled. Because of its excellent handling and performance characteristics, it has become a standard piece of equipment for use in towed fishing gear evaluations by the Harvesting Systems Branch, National Marine Fisheries Service, Mississippi Laboratories, Pascagoula Facility. In addition to fishing gear research, a number of other applications for diver operated sleds have evolved, including: Evaluation of towed instruments; biological, archeological, and geological surveys; and search and recovery operations. This report provides the information necessary to construct and operate a two-place diver's sled. It is not, however, intended to replace instruction or field training in sled operations. Construction Constructed entirely of aluminum, the two-place diver's sled has an overall length of 2.3 m (92 1/4 inches) and a width of 2.2 m (87 3/4 inches) (Fig. 1). Fully rigged, the sled's out-of-water weight is about 41 kg (90 pounds). Watertight welds and two attached side floats provide positive buoyancy. Materials Required 1) 87 feet 6 inches of 1-inch internal diameter (ID) schedule 10 aluminum pipe 2) 1 foot 10 inches of 1 3/8-inch ID schedule 10 aluminum pipe 3) Four 26 1/2- by 15 1/2-inch sheets of 3/16-inch aluminum 4) Two 46- by 14-inch panels of #36 nylon webbing 5) One spool of #42 (or #60) nylon twine 6) One 3/4-inch shackle 7) One 5/8-inch swivel 8) Two 14- by 6-inch plastic (or styrofoam) floats 9) 12 inches of 3.8-inch aluminum rod 10) Two 2-link sections of 3/16-inch chain 11) Two 3/16-inch lap links 12) Two 3/16-inch shackles 13) Two #3 snap hooks 14) Diver depth gauge 15) Bicycle flag and staff Sled Frame--Top Section The top section of the sled frame is constructed from 1-inch ID aluminum pipe (Fig. 2). The two outside frame members measure 84 inches long and are connected at the after end by a 50-inch pipe section. Forward, they are connected by two 19-inch pipe sections and a central "Y" section. The "Y" section is made with two 23 1/2-inch pipes which join with a central pipe measuring 64 inches long. The other end of the central pipe is attached to the middle of the 50-inch pipe. A 3-inch pipe is attached between the two "Y" members to later serve as an attachment point for a towing swivel. Sled Frame--Bottom Runners The bottom runners are made from two 110 1/2-inch lengths of 1-inch ID aluminum pipe (Fig. 3). The leading end of each pipe is bent into a half circle with an inside diameter of 14 1/2 inches. The runners are attached 9 1/2 inches inward on the two 19-inch forward pipe sections of the top frame. Sled Frame--Diagonal and Cross Members There are 12 diagonal members (Fig. 4). Six outside diagonals attach between the runners and the outside top frame, and six inside diagonals are attached between the runners and the middle pipe of the top frame. The outside diagonals are 17 inches long, and the inside diagonals are 21 inches long. They are attached at three points along the sled frame. The first set of four (two outside and two inside diagonals) is attached to the after end of the sled. The next set is attached 17 inches inward, and the last set is attached 62 1/4 inches inward from the aft end of the sled. Four 45 1/4-inch cross members are attached between the forward and middle sets of diagonals. The outside cross members are attached 6 1/2 inches down from the outside top section, and the inside cross members are attached 8 1/4 inches down from the middle pipe of the top section.Gameshttp://www.blogger.com/profile/14861068317417793607noreply@blogger.com