Drunken sailor? Effects of alcohol on the performance of ship operators.

The purpose of this study was to specify the effects of alcohol on the performance of ship operators as a contribution to the development of new strategies against the risks of alcohol in water traffic. The nautical performance of 21 captains before and after alcohol consumption was assessed on a ship piloting simulator. The simulated scenarios represented passages of a container vessel through the German Bight. Performance was examined by nautical instructors according to standardised protocols. Mean (S.D.) blood alcohol concentrations (BACs) of 0.100 (0.024) g/dl before and 0.100 (0.017) g/dl after the performance trial resulted in striking effects on the nautical performance. The categories most severely affected were foresight and analysis of situation (impairment in 18 of 21 cases), concentration (impairment in 16 of 21 cases), accurateness, risk disposition and navigation (impairment in 15 of 21 cases). Chart work, preparation and communication were impaired in 12, 11 and 10 of 21 cases, respectively. None of the participants were capable to operate the simulated ship with an adequate safety after ingestion of alcohol. From these findings, and in consideration of the well-established impairment of a multitude of mental and physical functions by alcohol, it can be concluded that even low BACs bear high risks in water traffic, a concentration above 0.1 g/dl will hinder a sufficiently safe performance of ship operators. This should be considered in alcohol education and legislation.

To what extent does the performance on ship simulators predict performance on real vessels?
Especially for ethical reasons, the effects of alcohol on the performance “onboard” cannot be investigated under real conditions. Simulation eliminates the risk of injury and property damage and is the only chance to achieve conditions at least close to reality by imitation of the complex demands on ship operators. From a technical point of view, the employed simulator replicates a real bridge perfectly. However, “simulator effects” may complicate the transfer of results onto true conditions. The participants were aware of the test situation and tried to compensate their alcohol-induced impairment. Thus the results might underestimate the effects of alcohol under real conditions. This risk of underestimation of alcohol-induced impairment has also been reported for flight simulator tests in studies on the impact of alcohol on the safety in aviation.

The effects of alcohol on the performance of ship operators

The observed effects of alcohol on the nautical performance were striking. The complex categories were most affected, namely the analysis of situations, foresight, concentration, navigation, risk disposition and accurateness (impairment in 15–18 of 21 captains). The categories preparation, communication and chart work which record more automated working processes were less affected (though also in ca. 50% of the participants). These results are in close agreement with the results of studies on alcohol and driving which prove an impairment notably in complex psychomotor tasks, even after alcohol doses that did not impair simple psychomotor task performance.

The impairment of nautical performance and the alcohol-induced mistakes can be explained by the well-established deterioration of a multitude of mental and physical functions by alcohol resulting in an impairment of perception, targeting foresight, attentiveness, flexibility, power of concentration, sense of responsibility and therefore in delayed, deficient or inadequate reactions. In this context, the recorded heart rates as well as the results of ophthalmologic tests performed during the experiments were interesting. The observed deterioration of optokinetic nystagmus, pupil reaction, accommodation and colour vision may cause mistakes and delays in the perception of data on the bridge, e.g. from navigation and radar systems. The continuously recorded heart rates revealed an attenuation of vegetative reactions in stress situations under the influence of alcohol. This may be due to an impaired perception of normally stress-inducing stimuli and to an alcohol-induced disinhibition with an inadequate reaction to such stimuli.

Three of the 21 captains exhibited an impairment in only 1–3 of 9 assessed categories. However, this was due to an extremely non-realistic, traffic-blocking, cautious performance as an attempt to compensate the intense perception of the negative effects of alcohol in the test situation. Though this abnormal attitude could not be recorded by the assessed categories, it indicated indirectly the intense negative impact of alcohol on the performance, as perceived by the captains themselves. In the test setting, these captains concentrated almost exclusively upon what appeared to be the primary task; this was “successful” in the assessed categories. It can be assumed that performance under these conditions will be seriously impaired in case of an emergency or other circumstances of increased workload. Similar observations in experiments with aircrew in flight simulator tests have been reported.

In the present study, BACs of ca. 0.1 g/dl during the performance trial were aspired. The actually observed BACs varied considerably, obviously because a meal was offered before the alcohol ingestion (to avoid hypoglycaemic, superposing negative effects on the performance). The drinking habits (as measure for the alcohol tolerance) of the participants varied substantially. Also captains with a presumably high alcohol tolerance and participants with relative low BACs exhibited a relevant impairment of performance. The latter finding confirms the assumption that ship operation is significantly impaired even at low BACs of ca. 0.04 g/dl.

Conclusion

None of the participants were capable to operate the simulated ship with an adequate safety after ingestion of alcohol. The observed impairment in the analysis of situations, in foresight, concentration, navigation, risk disposition and accurateness is not compatible with an adequate safety for men, property and environment in water traffic. This is true not only for the operation of container vessels, but also for other forms of commercial shipping and for recreational boating. According to the data of Howland et al. as well as to our data also relatively low BACs (at least above 0.04 g/dl) bear a high risk, BACs above 0.1 g/dl exclude a sufficiently safe performance in water traffic.

The risk of alcohol-induced impairment of performance in water traffic is still underestimated by jurists, mariners and the public; there is a need for information and education. With regard to the safety on water, to a predictability of legal decisions, and to the aim of a better prevention, an absolute BAC limit for water traffic should be established in Germany. An extension of the German road traffic BAC limit of 0.11 g/dl will not discriminate suspected persons, since a critical impairment of performance “onboard” can be assumed in virtually all cases with BACs exceeding this limit.