I suppose this is an obvious question, but I was curious about how shifts were managed during long ocean voyages in pre 20th Century sailing? Did they have 6 or 8 hour shifts? Did they just let things ride on calls nights (I guess not). Were there regulations or best practices? I know nothing about sailing...
In the time period I'm interested in, Royal Navy ships' crews were divided into two (or rarely three) watches, port and starboard, and stood watch in what was basically a four-hour rota. The watches were set as such (keeping in mind the naval day started at noon):
The dog watches allowed men to eat their supper, and also rotated the watches so that the men would alternate the first and middle watches (although in calm waters/undisturbed sailing there was a certain amount of napping on deck that was tolerated). There were men who were not part of this watch system who simply worked during the day, usually specialists such as the gunner, boatswain, cooper, sailmaker, carpenter and their respective mates; those men were called "idlers."
I've written more about this before if it's of interest: https://www.reddit.com/r/AskHistorians/comments/2xf2si/what_was_the_old_naval_hierarchical_duties_like/
During the age of sail they used a system of watchkeeping. That is, while in operation of the ship a group of men was always 'on watch'. This would be a series of positions/jobs that were kept going at all times. This would be things like the helmsmen, lookouts and duty officer. This would also include men who were basically on standby to move sails, haul on ropes, go aloft, pass messages, etc.
A standard watch was four hours long, alternating between two sets of crew. Traditionally divided between the starboard watch and the larboard watch. One watch would be on duty for their four hours while the other watch would be available to to other things, like clean, make and mend, etc. To keep the system fair, there were two shortened watches late at night. These were only two hours long each and called the 'dog watch'. This had two advantages, it caused the watches to alternate, so that the same watch wasn't always on watch during the same time of day. It also allowed the men to possibly get more than four hours of sleep at a time.
They were organized by a system of time keeping with bells. One station was to watch a half-hour sand glass. Every time it emptied, they were charged with turning it over and having a bell rang. Thus the time was split into half-hour bell rings. The bell would ring for each half-hour that had passed in that watch, up to eight 'bells' marking four hours and the changing of the watch.
Thus there were:
| Time | Watch |
|---|---|
| 2000 - 0000 | First Watch |
| 0000 - 0400 | Middle Watch |
| 0400 - 0800 | Morning Watch |
| 0800 - 1200 | Forenoon Watch |
| 1200 - 1600 | Afternoon Watch |
| 1600 - 1800 | 1st Dog Watch |
| 1800 - 2000 | 2nd Dog Watch |
Finally, there were a subset of men who did not stand watch, these were known as 'idlers'. These were the professional craftsmen of the ship who would work only during the day. This included men like the carpenter and his mates, the gunner and his mates, the surgeon, the bosun and his mates, etc.