Fatigue at sea in Swedish shipping—a field study

BACKGROUND: Today many merchant ships sail with only two nautical officers, working a shift schedule of 6 hr on and 6 hr off. There are concerns that such a shift schedule is related to fatigue. However, little data exist from onboard studies of seafarers. METHODS: Data were collected on board 13 ships. Fifteen participants worked on a 6-on, 6-off watch system and another 15 on a 4-on, 8-off watch system. Electrooculography, actigraphy, diaries, and reaction time tests were used to measure the effects of shift system on fatigue and sleep. RESULTS AND CONCLUSIONS: Sleepiness was higher during the night shift in the 6-on, 6-off system. Moreover, sleepiness increased more during the watch in the 6-on, 6-off system compared to the 4-on, 8-off system. There was a trend toward shorter sleep episodes in the 6-on, 6-off system and sleep was more often split into two episodes.