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 first two submarines in late 1996, before completely re-designed seals were fitted to the boats in late 1997, solving the problem.