Counting Time 30 minutes at a Time
“When modern sailors tried to “keep” time they found the sand-glass met their needs quite well. They used at least two or three variations. To keep track of their speed they used a device called a “Chip Log” which required a sand-glass of 30 seconds duration. To keep track of how long they worked, they used a sand-glass of 30 minutes duration. Now the duty time aboard ship, called a watch, is traditionally four hours, and this can be traced back to Egyptian times thousands of years ago, so you might expect a sand-glass lasting four hours. But this would be too heavy and the sand in it more likely to clog. Instead, sailors used a sand-glass of 30 minutes length. By the way, the content of the “sand” glass usually was not sand, but a mixture of ground-up sea shells, stone, egg shells, marble or other materials which would be less like to stick together than sand. A “glass” of an hour’s duration might also be found aboard ship.
To make sure the ship’s boy was paying attention, for it was usually his job to turn the sand-glass every 30 minutes, and to let everyone know the time, each time the glass was turned, the ship’s boy would ring the ship’s bell. It would be rung once for each half hour of a four hour watch. So after the second hour, four bells would be rung; after the third hour, six bells. To enable people’s ears to distinguish how many bells there were, they were rung in pairs, two rings at a time. When eight bells were rung, four hours had passed and the next watch hearing the eight bells would come up to relieve the crew currently working. The count would begin again with one bell being rung after half an hour into the new watch, and so on till eight bells would be rung again. With 24 hours in the day, there were six watch.”
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