Capt. Bill Brucato at MTVA (Master of Towing Vessel Association) has an post up about CEMS (Crew Endurance Management System) - CEMS and the tugboat quandary.
The article links to a USCG page Crew Endurance Management
Capt Brucato's points out that there are sharp limits to improvements given the six on six off watch schedule and the environment aboard a tug.
It's good that the Coast Guard is pushing the concept of Crew Endurance. When I was towing, endurance was seen as a matter of will power and toughness.
I sailed mate on the Chilkat Chief on what Capt Brucato calls the "back watch" (the midnight to 6 am and the noon to 6 pm). Capt Brucato points to maintenance issues as one stumbling block to proper rest. On the Chief we did no preventative maintenance on deck so that was not the issue. The bugaboo was cargo operations.
The Chief pulled a tank/log barge, we would load gasoline at Cherry Point Washington and discharge it in various ports in South East Alaska. We would then tow the empty barge to Thorne Bay load logs for two day. The barge held about 700,000 board feet of logs. We then towed the barge to Ward Cove just north of Ketchikan for discharge. Then we would load a second time(at Long Island Ak?) and take the load to Port Angles Washington. After discharging we would spend a day in Seattle cleaning the bark off the barge and then, after a night in town, off to Cherry Point for another go round.
Because cargo operations were done during the day, and as mate I had to work any time cargo operation were conducted, I really caught it. If cargo operation finished, at say 8 pm, it might be 9:30 pm before I could get to my room then up at 11:30 for the mid to 6.
I don't recall how many hours I worked consecutively but I do recall one morning I was pulling a load of gasoline, approaching Snow Pass at the South West corner of Zarembo Island, when I experienced an episode of microsleep.
I was getting set down on the reef by current and had adjusted my course to port a couple of times when I suddenly found myself too close to the reef. It was like watching a movie with part of a scene missing. One instant I was ok and the next I was too close.
There is a lighted rock in Sumner Strait on the north side of Snow Pass called "The Eye Opener" - maybe someone on the back watch southbound had a similar experience.