A friend asked me for: Brief Treatise on watches and bells at sea ...

Traditionally, a watch is 4 hours long. In the Navy they are named, in the merchant navy they are referred to by the hours they span.

Bells are rung at the end of each half hour, starting with 1 bell at 30 minutes into the hour, 2 bells an hour into it etc. 8 BELLS marks the end of each watch (and thus the start of another)

In the Navy the watch between 4pm and 8pm (1600 to 2000) is split into two 'dog' watches and whilst the bells follow the above rule, 4 bells is rung at the end of the first dog watch and 8 at the end of the last dog.

Bells are rung in pairs (eg five bells is rung "ding-ding, ding-ding, ding"

By tradition, 16 bells (two groups of 8) are rung at midnight on New Year's Eve. 8 bells for the old year and 8 for the new. They are traditionally rung by the youngest person on board.

See table below: