Watches and bells

Note: all times are based on the 24 hour clock, midnight to midnight. But, see Nautical time and civil date and GMT, Universal, Civil and Atomic

While the origins are somewhat uncertain, but date back at least to the fifteenth century, a "watch" is traditionally a time period of four hours, during which half the crew (the "Port Watch" or the "Starbord Watch") is on duty (working, on deck, etc - "on watch") and the other half is resting ("off watch").

The evening watch, from 1600-2000 hours (4pm to 8pm) is further subdivided into First and Last Dog watches (Second Dog watch in the US Navy); this gives an uneven number of watches each day, so that the crew alternates the "graveyard" watch (starting at midnight, this is normally the least popular time to be on duty) and also serves for the evening meal.

Bells are used to mark the time during the watch, and are based on turning a half hour watch glass (a figure-of-eight or double-bubble hourglass holding a known quatity of sand); at the first turn on each watch the bell would be struck once, on the second turn twice, etc ..., with the sounds grouped by pairs:

Note: The end of the watch is considered at 8 bells, hence the saying "Eight bells and all is well."

See also "Time at sea"