Design, Fabrication and Evaluation of an Experimental Diver-Operated Construction Assistance Vehicle

Abstract

Abstract An experimental diver-operated Construction Assistance Vehicle (CAV) was designed, fabricated and evaluated to determine the utility and general specifications for a prototype diver work vehicle. The CAV, fabricated from off-the-shelf components, is capable of carrying 1300 pounds of wet-weight cargo between the surface and the ocean bottom work site. The craft's pneumatic and hydraulic power is available to operate hand power tools. Over one hundred test dives were conducted in the ocean. During these tests, a maximum depth of 110 feet was reached. Operational testing proved the CAV to be a safe and effective means for both delivering cargo and powering diver tools. Introduction Under the sponsorship of the Naval Facilities Engineering Command (NAVFAC), the Naval Civil Engineering Laboratory (NCEL) has been engaged in developing safe and reliable diver work systems for use by naval underwater construction forces. As a portion of this program, NCEL has developed a Construction Assistance Vehicle (CAV) which provides working divers with an underwater "pickup truck" capable of short-haul transportation of tools, power supplies, equipment and personnel between the surface and the underwater construction site. The CAV (Figures 1 and 2) is 26 feet long with a ten-foot beam. To minimize development costs the catamaran-hulled vehicle was fabricated primarily from mild steel and equipped ith off-the-shelf components. Two SCUBA divers operate the free-flooding submersible from a cockpit located in the bow (Figure 3). The aft section consists of a 4-1/2 × II-foot deck which can accommodate up to 1300 pounds of wet-weight cargo. Two ballast systems are provided to obtain neutral buoyancy during submerged operation and to compensate for changes in cargo weight. Primary power for the electro-hydraulic propulsion system is supplied by lead-acid batteries. Thrust for propulsion is provided by two articulated hydraulic motors located on angled struts above the cargo deck and two fixed hydraulic motors located aft and just below the main hull structure. Since there are no movable rudders or diving planes, steering is accomplished by controlling the speed and direction of the propulsion units. This paper describes the design, fabrication and evaluation of an experimental CAV which was developed to determine the utility of the concept and to serve as a test-bed vehicle for the evaluation of other underwater construction tools, Description Of The Vehicle Structure The CAV is a catamaran-hulled vehicle fabricated primarily from mild steel. The main hull structure consists of two longitudinal 26-inch I.D. cylindrical tubes that run the length of the craft and four transverse tubes that tie the hull together. Most of the submerged buoyancy is provided by these tubes which were designer for a collapse depth of 250 feet. Ballast The main ballast tanks are located below the longitudinal main hull tubes. The primary function of the main ballast tanks is to provide 5000 pounds of buoyancy for surface handling of the vehicle. In addition, the tank structure functions as a landing skeg and as a support for the trim weight system. These tanks are completely flooded when the vehicle is submerged. Two auxiliary ballast tanks, integral to the main hull structure and centered at the cargo deck, provide a variable seawater ballast capability to compensate for changes of cargo weight. The auxiliary system is also used for correcting port and starboard trim. Water is transferred to and from the sea and between the tanks by means of a hydraulic driven pump. Pneumatic System A schematic of the vehicle's compressed air syste