The U.K. Maritime and Coastguard Agency has released a research report into the eight hours on / eight hours off (8/8) watch keeping system which indicates it is preferable to a 6/6 system.
The aim of the study was determine what affect the system had on seafarer fatigue, performance and safety and included a comparison with other typical watch keeping systems.
The 6/6 watch keeping regime was found to be worse than the 8/8 watch keeping regime in terms of the quantity and quality of sleep obtained. Levels of sleepiness, stress, and fatigue were lower with the 8/8 system.
It was only between 02:00 and 04:00 at night that sleepiness levels were higher under the 8/8 system. During this 02:00 to 04:00 time interval those working 8/8 have been awake since 20:00, while those working 6/6 only since 00:00. Hence, less sleep pressure has built up in those working 6/6 between these time points.
The story was completely opposite for the 04:00 to 06:00 time interval. Here, 8/8 watch keepers had just woken up, while 6/6 ones had been awake since midnight.
Clear peaks in sleepiness were observed when the end of watch coincided with hours in the night and early morning, i.e., at midnight at the end of the 18:00 to 00:00 watch, at 04:00 at the end of the 20:00 to 04:00 watch, and at 06:00 at the end of the 00:00 to 06:00 watch.
40 watch keepers from five vessels participated in the study. They started working either under a 6/6 or 8/8 regime for three weeks. After three weeks leave, they then worked under the other regime.
A separate study also investigated the working patterns of selected tug crews. In this study, the 4/8 three-watch system was shown to be at relatively low risk compared to other systems.
The vessel report is available here.
The tug report is available here.