BIMS – Becker Intelligent Monitoring System
05.07.11
Modern dynamic positioning systems (DP) and auto-pilot systems (AP) utilise a variety of input signals to maintain course or position, e.g. from positioning reference sensors, combined with wind sensors, motion sensors, gyro compasses, GPS data, etc. These data are processed by an IT system to allow the course or drift to be predicted and to calculate countermeasures controlling the actuators in the vessel’s propulsion system. Input data and processing is of high quality, but only reflects the vessel’s motion response. Inertia causes a massive decrease in the strength of these control signal, which do not meet or provide sufficient quality for manoeuvring. For rudder-propeller arrangements
relatively high corrections were applied to rudder angle, resulting in the generation of high rudder forces. The vessel turns more than necessary for the predicted course correction, resulting in a similar counteraction in the opposite direction. This effect results inhysteresis, or rudder flipping, causing the steering gear to work continuously and more or less strong fluctuations around a set course or position.
Source: The Maritime Executive (press release)