A comparison between the 3/9 and the 5/10 watchbills

Abstract

This is the second phase of a longitudinal study comparing the fatigue levels, workload, and performance of crewmembers working on the 3-hrs on/9-hrs off (3/9) and the 5-hrs on/10-hrs off (5/10) watchstanding schedules. Detailed results on the 5/10 are included elsewhere (Shattuck, Matsangas, & Powley, 2015). Crewmembers from the Reactor Department on the USS NIMITZ (N=117, 24.6±3.89 years old, 95 males, 109 enlisted, with 4.25±2.65 years of active duty) participated in this study. Results show that the 3/9 is better than the 5/10 in terms of sleep quality, subjective levels of fatigue, mood, psychomotor vigilance performance, and acceptance by the Sailors. Although crewmembers on both the 5/10 and the 3/9 received, on average, approximately seven hours of sleep per day, the sleep hygiene and acceptance of the two schedules differ considerably. On the 3/9, significantly fewer Sailors reported not having enough time to sleep, as contrasted with the 5/10 (3/9: 52%; 5/10: 88%; p<0.001). There were differences between crewmembers on the two schedules in the expression of negative opinions about the adequacy of their sleep (3/9: 30%; 5/10: 80%) with over twice as many negative opinions for the 5/10 group. Daytime sleepiness and mood states deteriorated during the underway when using the 5/10, whereas daytime sleepiness and mood states of Sailors on the 3/9 did not change. Crewmembers on the 5/10 also had lower psychomotor vigilance performance than their counterparts on the 3/9 schedule (15% longer reaction times and 59% more 355-millisecond lapses greater combined with false starts). Crewmembers on the 5/10 also had lower psychomotor vigilance performance than their counterparts on the 3/9 schedule (15% longer reaction times and 59% more 355-millisecond lapses greater combined with false starts). Overall, these results may be explained by considering the timing of sleep and the periods of sustained wakefulness experienced on the 5/10. Over a 3-day rotation cycle, a crewmember on the 5/10 watchstanding schedule sleeps at three distinctly different times on each subsequent day, experiences two periods of sustained wakefulness, and has one night with only a 4-hour opportunity for sleep. In contrast, Sailors on the 3/9 have a fixed sleep schedule every day and they experience, at most, 16- to 17-hour periods of sustained wakefulness. Even though the 3/9 schedule, as a whole, is better than the 5/10, analysis showed that two 3/9 watch sections, those standing the night watches, were accepted less by the Sailors. We postulate that concerns about the implementation of the 3/9 schedule may be ameliorated by adjusting sunlight exposure, providing sleep hygiene training, and by considering an alternative distribution of duties between watch sections to allow protected sleep times for those on night watch duty.