Health condition of crews and length of the period of sailing to the tropics.
D000328:Adult; D002908:Chronic Disease / Q000453:epidemiology*; D005767:Gastrointestinal Diseases / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009326:Naval Medicine; D012140:Respiratory Tract Diseases / Q000453:epidemiology; D014330:Tropical Medicine