Steering Gear Refit Project: M.V. Fairweather
After 30-50 years of service, even well-built steering systems usually require refit or upgrade. This is particularly true of control systems due to rapid improvement in control and monitoring. With over 70 years of experience in design and manufacture as well as extensive knowledge of different makes of steering, Autonav is in an ideal position to provide cost effective and reliable upgrades without the need to replace the complete system. With this knowledge and experience, Autonav can evaluate which part can be retained, which part needs to be repaired, and which parts needs replacement.
A typical example is recent refit of 231 feet length (70.4 meter) National Oceanic and Atmospheric Administration research vessel M.V. Fairweather. This vessel was built in 1968 and controlled by a mechanical different linkage dating back to the 1940s. This was of a dual loop type in which electric commands from the bridge operated a directional solenoid valve which powered a hydraulic reversing motor with geared input to the mechanical differential. This summed bridge commands with the rudder position and for any difference, it would adjust the stroke of a variable volume reversible flow pump to move the rudder to the commanded position. Any slight misalignment of this linkage would cause it to jam and drive the rudder hard over. Having solved this problem on a sister ship, Autonav was requested to attend the vessel and effect a temporary repair so the vessel could complete an ongoing survey task. Later a new Autonav control system, autopilot and pumpset was built to control the rotary vane steering actuator for future reliability and maintainability. Due to slack, friction, and delays in the original mechanical control system, the autopilot could not steer more accurately than +- 5 degrees.
The new Autonav control and autopilot was able to hold a course accuracy of +- 0.10 degrees on sea trials. This control accuracy resulted in a significant reduction in fuel consumption and improved reliability and manoeuvrability. An additional benefit was the elimination of the weight and space requirements of mechanical tie bars and tillers due to the use of electronic rudder synchronization. This coupled with a rudder speed improvement from the original 28 seconds to only 10 seconds as well as independent rudder control also allowed the vessel the possibility of future addition of Dynamic Positioning.