Work and rest patterns and psychomotor vigilance performance of crewmembers of the USS Jason Dunham: a comparison of the 3/9 and 6/6 watchstanding schedules

Abstract

This study compares the patterns of crew rest and sleep, psychomotor vigilance performance, and work demands/rest opportunities afforded by two different schedules, the 3-hour on/9-hour off (3/9) and the 6-hour on/6-hour off (6/6) watchstanding schedules. The study was conducted aboard the USS Jason Dunham, a U.S. Navy destroyer operating in the vicinity of the Persian Gulf during the months of November and December 2012. Of the 122 participants in the overall study, 52 were shift workers using either the 3/9 (n=41) or the 6/6 (n=11) schedules. These 52 individuals are the focus of the current analysis. Although sleep deprivation was evident in both watch schedules, results show that crewmembers on the 3/9 received more sleep than their peers on the 6/6, with 6.46 + 0.77 hours versus 5.89 + 0.87 hours, respectively. The 3/9 schedule, compared to the 6/6, was also better in terms of the distribution of sleep episodes across the day. Specifically, crewmembers on the 3/9 received more sleep during nighttime hours, whereas crewmembers on the 6/6 had to sleep during the day to compensate for their lack of sleep during nighttime hours. In terms of work demands, crewmembers on the 6/6 schedule have considerably long workdays, with, on average, 15 hours on duty, which corresponds to approximately 30% more time on duty than allocated in the Navy Standard Work Week (NSWW) criterion (on average, 105 hours compared to 81 hours weekly). The two schedules differed significantly in the variability of psychomotor vigilance performance; specifically, crewmembers on the 6/6 schedule had larger variability than those on the 3/9 in 11 of the 13 Psychomotor Vigilance Task (PVT) metrics analyzed (p<0.05). The average value of the PVT scores was better on the 3/9 compared to the 6/6, but not at statistically significant levels. The findings of this study show that the 3/9 is better than the 6/6 in affording rest and sleep opportunities, sleep hygiene, fatigue levels, psychomotor vigilance performance, work demands, and acceptance from the participants.