Human control of ships in narrow fairways

The ship navigation task may be considered as a hierarchically structured task. The voyage is prepared at a planning level. The progress is monitored and controlled at an execution level. A better understanding of the ship handler's performance is needed for various reasonst mainly originating from ongoing trends of automating navigational tasks. This article is focussed on the monitoring and the controlling of a ship's path in narrow fairways. Within this scope hypotheses are tested by means of experiments in a ship manoeuvring simulator. It is suggested that the ship handler's control behaviour is based on two complementary elements: preprogrammed control and feedback control. Notions on preprogrammed control are primarily based on stimulus-related control settings. Notions on feedback control are primarily based on the evaluation of the results of a control setting. The correctness of performance is continuously checked against a reference (perceptual memory). This element is relevant in those manoeuvres in which feedback can lead to accurate performance. Results of experiments on feedback control support the hypothesis of perceptual memory. The development of perceptual memory is shown as a function of practice in a tracking task. A slight motor memory development, contributing to the timing of control actlons, can be noticed. It is concluded that the ship handler's accurate performance is primarily based on perceptual memory with emphasis on the accuracy of references for evaluating the correctness of performance. Preprogrammed control is rather inaccurate.