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Planning and Implementation

As you plan to change your watchbill, consider these important

Planning Factors

  • Type of rotation: Circadian is almost always better
  • Length of watches: Shorter is usually better (it is easier to maintain alertness for 3 vs 6 hours)
  • Number of sections: More is usually better (a 4 section watch is better than 2 or 3-section)
  • Rotation times: Cardinal points are simpler (use the hours of 12, 3, 6, and 9 on an analog clock face)
  • Direction of rotation: Forward is usually better (staying up an hour longer and sleeping in an hour in the morning is easier than going to bed and waking up an hour earlier)
  • Designated sleep times: Sleep at same time each day (work with your body's natural 24-hour rhythm)
  • Number of days in each rotation: Three weeks or more is better (some ships wait until port call to shift)
  • Day of rotation change: Weekends generally allow more flexibility with Sunday or holiday schedule
  • How to rotate: Lengthen the day by an hour or so rather than making a drastic change (shifting 6 hours takes about a week to completely adjust)


  • Heat stress limits (use PHEL curves to determine limitations for hot environments)
  • Drills, briefs and debriefs (who needs to attend and when to hold them)
  • Watch turnover SOP (crisp turnover procedures are important)
  • Pre-watch plant tours (if required, will lengthen turnover time)
  • Watch team cohesion (ensure your watch team has adequate time to bond)
  • Meal hours (galley hours may need to be extended to support a new watchbill)
  • Daily routine (design the work day so that watch and work or included in the plan)
  • Berthing arrangements (putting the same watch team together in berthing can reduce noise and unnecessary sleep disruptions)


Employing more effective watch schedules leads to increased endurance! 

For example, in the 3/9 watchstanding schedule, Sailors stand 2 watches each day, separated by 12 hours. The 4-section schedule rotates every 3+ weeks—probably on Saturday or Sunday--or coinciding with a port visit. As shown here, on Saturday evening, Sections 1, 2 and 3 each stand a 4-hour watch and then roll forward into their standard 3-hour watch the following day.

Advantages include: easy to remember watch assignment, everyone stands 6 hours of watch per day in two 3-hour blocks, no one stands longer than a 4 hour watch, no back-toback watches, at least 9 hours off between each watch. Note: on the day of rotation, one watch section gets 12 hours off, one gets 11 hours off and one gets 10 hours off before standing watch.


  • Shorter watches --> better focus
  • Stable routine --> more predictability
  • Circadian sleep pattern --> better quality of rest
  • Reduced heat stress --> better effectiveness 
  • Watchteam alignment --> better training, coordination
  • Sailors prefer the 3/9 watch rotation

Some Negatives:

  • More watch turnovers 
  • Repetitive watch cycle (potentially see same thing every watch)
  • Must modify standard ship’s routine (culture shift)


  • Institute crisp watch turnover policy
  • Watch rotation plan needs to be specified -- including the direction and duration of rotation
  • Leadership support and flexibility to adjust the plan


Little known facts about the 3/9:

The Roman Legions used the 3/9 nearly 2000 years ago!

In Rules for Encamping an Army from the “De Re Militari” or The Military Institutions of the Romans by Flavius Vegetius Renatus written in 390 A.D. and translated in 1767 by Lieutenant John Clarke.




“Then the legions and auxiliaries, cavalry and infantry, have the ground distributed to them to pitch their tents according to the rank of the several corps. Four foot-soldiers of each century and four troopers of each troop are on guard every night. As it seemed impossible for a sentinel to remain a whole night on his post, the watches were divided by the hourglass into four parts, that each man might stand only three hours. All guards are mounted by the sound of trumpet and relieved by the sound of cornet. The tribunes choose proper and trusty men to visit the different posts and report to them whatever they find amiss. This is now a military office and the persons appointed to it are called officers of the rounds.”


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Crew Endurance Team
Naval Postgraduate School


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Share Your Experiences

If you have been on a ship that implemented a circadian-based watchbill, consider sharing your experience with the fleet.  

Contact the Crew Endurance Team at NPS to pass along Lessons Learned and Success Stories.