the dorsal fin and create a more streamlined integration of the dorsal to flat upper Hull deck section. and 2) To 'fill in' the hollow section of hull aft of the bow curvature. Both these could be achieved with Carbon Fibre or Fibreglass covers as no load bearing strength would be required. Subsequent studies by the DSTO showed that the submarine's hull shape, particularly the redesigned sonar dome, the fin, and the rear of the submarine, focused the displaced water into two turbulent streams; when the seven propeller blades hit these streams, the propeller's vibration was increased, causing cavitation. These problems were fixed by modifying the casing of the submarine with fiberglass fairings. Propulsion system During trials of the first submarines, the propulsion system was found to be prone to failure for a variety of reasons. Most failures were attributed to the fifteen-tank diesel fuel system: the tanks were designed to fill with salt water as they were emptied to maintain neutral buoyancy, but water would regularly enter the engines due to a combination of poor design, gravity separation of the fuel and water being insufficient, and operator error resulting from poor training. Problems were also caused by bacterial contamination of the diesel fuel, which, along with the salt water, would cause the fuel pumps to rust and other components to seize. The fuel-related issues were solved by installing coalescers, improving training and operational procedures, and adding biocides to the fuel. Propeller shaft seals were a significant problem on Collins and Farncomb. Although designed to allow for a leak of per hour, during trials it was found that the seals would regularly misalign and allow hundreds of litres per hour into the boat—during one deep diving test the flow rate was measured at approximately a minute. ASC claimed that solving these problems could be done by manually adjusting the seals as the submarine dived and rose, but this would have required a sailor dedicated solely to that task, affecting efforts to minimise the required number of personnel. It was found that the problem could be temporarily alleviated by running the propeller in reverse for 100 revolutions, pulling the seal back into alignment, although a permanent solution could initially not be found, as ASC refused to accept responsibility for the problem, and the original manufacturer of the seals had closed down. New suppliers were found, with modified seals fitted to the