Basic research on navigator fatigue and lookout performance

Numerous ship collisions occur due to navigator errors such as improper lookout in a navigational watch, which is considered an error in the situation awareness (SA) of a navigator. Moreover, mental workload is considered one of the causes of human error, and navigators are often under a high mental workload onboard, experiencing fatigue and stress. The aim of this study was to confirm that the coefficient of variation of R-R interval (CVRR) and the adaptive weighted workload (AWWL) of the National Aeronautics and Space Administration Task Load Index (NASA-TLX) are effective indexes to measure navigator fatigue. Another aim was to show the effect of fatigue on navigator SA in lookout. Thus, subjective and objective mental workload of navigators caused by fatigue was measured in bridge simulator experiments. Navigator SA was measured by using a Situation Awareness Global Assessment Technique (SAGAT). The results of the experiments were shown that CVRR was confirmed as an effective objective index for measuring navigator fatigue. Further, navigator SA errors are likely to increase under fatigue conditions.