The Seth Thomas “Helmsman” ship’s bell strike clock has been popular for many years. It was introduced in the late 1950s or early 1960s, and made into the 1980s or longer.
The Helmsman uses a movement made by Hermle in Germany. The movements made in the 1960s have the patent number 2,974,473 stamped on the back plate. The patent describes a system for doing the ship’s bell strike. See this web page for strike examples. Ship’s bell striking operates on a four hour cycle with pairs of bell strikes on each hour, and pairs of strikes plus a single strike on the half hour:
12:00 XX XX XX XX
1:30 XX X
2:00 XX XX
2:30 XX XX X
3:00 XX XX XX
3:30 XX XX XX X
4:00 XX XX XX XX
and so on, repeating every 4 hours.
The inventor of the patent is Richard Kramer, and the patent was assigned to General Time Corporation (parent company of Seth Thomas at that time).
The fact that General Time, and not Hermle, received the patent, leads me to believe that this movement was specially made for Seth Thomas. Later, of course, other companies used this movement in their clocks (including the Chelsea “shipstrike” clocks).
One interesting feature of Kramer’s design is that a “dummy” strike without the bell is performed at 15 minutes before the hour. This prepares the strike for the next hour, when 1, 2, 3, or 4 pairs of strikes are sounded. In later years, the design was changed, and the “dummy” strike cycle was eliminated.