Half hour sandglass from the wreck of HMS Invincible, before 1758
A sandglass was a method of keeping time at sea, this helped keep track of watches on deck, regulating life on board. During sea passages, the naval watch system divided 24 hours of the day into six four-hour watches with half the ship’s company on watch and the other half off duty. Each four-hour watch was marked every 30 minutes by ringing the ship’s quarterdeck bell.
After the first 30 minutes, one bell would be sounded; thirty minutes later two bells, and so on up to eight bells at the end of the four-hour watch. The circular ends are all made of turned oak marked with a large broad arrow.
The vertical posts are made of pine. The two bowls are separated by a brass control disc with a small central hole and bound together with a sail maker’s whipping.
