Evaluating the motions of a semi-submersible platform with respect to human response.

The motions of a semi-submersible drilling platform have been evaluated so as to predict the effects on the comfort and activities of the crew. The horizontal motions at the drill floor exceeded the 'average threshold of perception' defined in International Standard 6897 (ISO 6897, 1984) by more than a factor of two; they were about half of the limit for the worst 10 min in five years for 'fixed offshore structures where work of a somewhat critical nature is carried out'. Other standards predict that the vertical motion would cause vomiting due to motion sickness in less than 5% of unadapted adults within the first 8h of exposure. The calculated probability of 'motion-induced interruptions' (loss-of-balance events) caused by deck motion was negligible. Notwithstanding the above conclusions, it is considered that current standards are insufficient to predict the effects of the motions of ships and floating platforms on the activities of the crew.