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Timekeeping Aboard Titanic

Note: to avoid confusion, the word "watch" in this text refers only to either a four-hour period of duty, or to the men who worked during those four hours. The word "timepiece" refers to pocket watches used by gentlemen.

Timekeeping is based on the assumption that the earth turns exactly one revolution, or 360 degrees every 24 hours. This amounts to 15 degrees of longitude every hour. For the courthouse clock noon today day comes 24 hours after noon yesterday.

Unfortunately, the Earth does not rotate quite so precisely. Some days are longer or shorter by a small amount that can be ignored in daily life. The standard 24 hour day is known as "mean time." Navigators must apply a correction known as "the equation of time" when using the sun for navigation.

Things are not so neat for a ship like Titanic making a westbound passage. The courthouse never moves, but the ship steams some distance west between noon longitudes from day to day. This distance means that today's "high noon" comes a few minutes later than it did yesterday. (The reverse is true for an eastbound voyage. Here we will focus only on westerly trips because Titanic was going west.)

"High noon" on land is known to navigators at sea as "local apparent noon" (LAN). Both terms refer to the instant when the sun crosses the observer's meridian. This means the moment when the sun is at its zenith (highest point) for the day. Titanic used its LAN to establish shipboard time each day. At 22 knots Titanic moved west at the rate of not quite one degree of longitude (at 42º North latitude) every two hours. In 24 hours, it moved roughly 12 degrees which is equal to the rotation of the Earth in 8/10ths of an hour. On Sunday, April 14 the ship's westward movement worked to be 47 minutes. Those extra minutes were part of Sunday, so had to be "tacked on" to the end of the day. This meant the Sunday of Titanic's accident was to be 24 hours and 47 minutes long.

Navigators and astronomers use noon as the marker for the start of their "astronomical day" because the sun is visible in the sky. It was necessary to use noon to because prior to electronic navigation it was impossible to measure midnight. The familiar "civil day" starts at midnight 12 hours before the astronomical day. For example, 2 a.m. January 9 in civil time is the same as 2 p.m. January 8 in astronomical time. It would have been disconcerting to its guests if Titanic had changed day and date using the astronomical day. Passengers commonly used the civil day in their lives ashore, so thought of "midnight" as the start of the new day. In deference to passengers, Titanic adopted the civil day for ship's time.

By definition, "midnight" starts the new civil day. On shore it is no more than the tick of a clock. For Titanic, however, "midnight" was effectively a span of time rather than a single instant. This arose out of the need to set the ship's clocks back each night to match the ship's westward movement. Instead of a single tick, "midnight" was effectively became 47 minutes on the night of the disaster. This elongated "midnight" started at 12 hours after the ship crossed its noon longitude on Sunday, April 14th. It continued for those extra 47 minutes until civil midnight marking the start of Monday, April 15th.

While this may seem confusing, 47 minutes of midnight would not have been a problem for anyone except the ship's navigator if it were not for the need to share those extra minutes among the deck crew. Titanic's crew was divided into two "watches," the port and starboard. Each watch was to share about half of those extra 47 minutes. The starboard watch was to serve its time before and the port watch after the "midnight" change of watch. Second Officer Charles H. Lightoller confirmed this and explained that all clocks aboard Titanic were to be correct for April 15 noon at midnight. His statement meant that both the passenger and crew clocks would have been properly set back prior to civil midnight starting the new day.

It is obvious from Table A-1 why the “midnight” change of watch for the crew had to come 24 minutes after 12:00 o’clock in April 14th time or 23 minutes before 00:00 o'clock in April 15th hours. This required retarding crew clocks in two stages, each equal to the extra time served by its respective Watch. Hence the name “two-stage” for this method of time keeping..

Most sailors did not carry expensive and fragile pocket timepieces in 1912.  It would have been extremely confusing if the extra time was added after 8 bells. Men without pocket timepieces would not have been able to gauge 23 minutes while standing duty away from any of the ship's electric clocks.

Time Of Crew Change Of Watch

Table A-1

Table A-1 shows why the "midnight" change of watch had to take place midway between April 14th and April 15th civil time. This was the only way to split the 47 extra minutes equally between the port and starboard watches. However, this arrangement brought up the problem of ship's bells. Each watch started at 8 bells of the previous watch. One bell was then struck for every passing half hour. Two bells meant the first hour of the four had been worked. Four bells announced the halfway point. An immutable part of this timekeeping system was that 8 bells always marked the change of watch when the men on duty could go below for a few hours of rest. Table A-2 shows the traditional sequence of bells.

Table A-2

Note: Dog watches in Titanic followed British naval tradition. The first dog watch (4-6 p.m.) ended at "4 bells." The bell sequence for the second dog watch (6 to 8 p.m.) then re-started so that it also ended at "4 bells." This tradition eliminated "8 bells of the second dog watch," the infamous time of a mutiny during the Napoleonic wars.

However, adding those minutes within the schedule would not have been so confusing because of the way sailors really used their bell system. Hearing six bells did not tell a sailor he had served three out of his four hours on duty. Rather, he would have understood six bells as announcing one hour remained before change of watch.

White Star Line regulations allowed clock adjustments to start at 10 p.m. each night. Although this was late enough not to both passenger activities, the real reason for choosing that hour was convenience of the crew. Note that 10 p.m. is the midpoint of the 8 to 12 p.m. watch. Adding extra time in the middle of a watch would allow sailors to continue using ship's bells to measure their remaining time on duty. At 10 p.m. the crew's bridge clock was turned back to 9:36 p.m. This increased the normal 30 minute duration between four and five bells to 56 minutes. Even so, when 5 bells was struck, the crew knew it had an hour and a half remaining before the midnight change of watch. Table A-3 shows how adding the extra time at 10 p.m. would have allowed the starboard watch to serve its extra time and the ringing of 8 bells to mark the change of watch.