Motion sickness incidence on sea-going passenger vessels
The research reported in this thesis was undertaken to increase understanding of the occurrence of motion sickness on board ships at sea. It was intended to discover whether seasickness was related to vessel motion and, if so, to attempt to define the nature of such a relationship. The vessel motion variables of magnitude, axis, frequency and duration were considered in addition to personal variables including age and sex. A critical survey of the literature shows that, although some laboratory studies of motion sickness have been conducted, little research has been reported involving passengers at sea. The few studies that have been undertaken hitherto on board vessels have generally used unsatisfactory techniques for either motion measurement or sickness measurement. Current theories of motion sickness were found to produce few specific hypotheses concerning sickness on ships at sea. An ecological theory of motion sickness causation by gravitational disturbance is discussed. Motion sickness was investigated by means of surveys of passengers on sea-going ferries. Measurements of vessel motion and seasickness were made on six ships, from 1,255 to 14,368 tonnes, two hovercraft, and a hydrofoil. Motion measurements were made on 114 voyages of durations between 1/2 hour and nine hours. Data on sickness amongst passengers were obtained from 20,029 respondents to questionnaire surveys conducted on each voyage. Information was collected on the occurrence of vomiting, illness rating, time of onset of symptoms, the taking of anti-seasickness tablets, the consumption of alcoholic drinks, regularity of travel by sea, age, and sex. Both vomiting incidence and illness rating were greater in females than males, and there was a decrease in sickness occurrence with increasing age. People who travelled rarely by sea were more likely to be sick than more regular travellers. The incidence of sickness was related to the taking of tablets and the drinking of alcohol. Anecdotal information was also gathered from passengers, and consideration is given to the effects of environmental variables. The incidence of seasickness amongst passengers was found to be closely related to the motion of the vessel. Vomiting incidence and illness rating were linearly related to the root mean square magnitude of the vertical z-axis acceleration occurring at about 0.2 Hz. Sickness increased with increasing duration of exposure, and a measure of motion `dose' is proposed as a method of combining the variables of stimulus magnitude and duration. The high frequency motions measured in the hovercraft were found to be less provocative of sickness than similar magnitudes at lower frequencies. Motion in axes other than the vertical correlated less highly with sickness, although some intercorrelation between motion axes was evident. The results of the research show approximate agreement with previous laboratory studies. The combined data have been used to develop a procedure for predicting seasickness occurrence in marine vehicles and other forms of transport where low frequency oscillations are encountered.