The bridge chronometer and the engine room clock are both set from the same radio time signal and checked against each other at every departure, because the log books they stamp are legal records. On the evening crossing, and only that one, the engine room clock falls four minutes behind the bridge for about half an hour and then catches up, with no adjustment by anybody.
I am the chief engineer on a ferry, and the engine room clock is my clock.
How the clocks are kept.
The bridge has a chronometer and the engine room has a clock, both electronic, both set from the radio time signal, both checked against each other at each departure and the check written in both logs. Every engine movement, every alarm, every order from the bridge is timed in the engine log by my clock and in the bridge log by theirs, and the two logs are the ship's account of itself.
A clock that drifts is replaced. A drift of four minutes would be a clock in a bin.
On the evening crossing, my clock falls four minutes behind the bridge.
It starts about forty minutes out, the two drift apart over ten minutes to a four minute difference, hold there for about half an hour, and then close again over ten minutes, so that by arrival they agree to the second, as they did at departure.
Nobody touches either clock. I have stood at mine and watched it.
Watched it is the wrong phrase. A clock that loses four minutes over ten minutes is running at a bit over half speed, and you cannot see a second hand run at half speed without seeing it. I have stood with my watch beside my clock and my watch ran at the right speed and the clock's seconds ran at the right speed and the clock lost four minutes.
I know how that sounds. I have written it down that way because it is what I saw.
What has been checked.
The clock. Replaced twice. The new clock does it.
My watch. It does not lose. Neither does the bridge's, nor the phones of the crew, nor the engine control system's own timestamps, which come from a satellite receiver and which agree with the bridge.
So it is the engine room clock and only the engine room clock, and it is the evening crossing and only the evening crossing, and it is the stretch in the middle, over water I could point to on the chart.
The engine log.
Every entry in my log on that stretch is four minutes earlier than the same event in the bridge log, and when the two are read side by side, which they are, quarterly, by the superintendent, it looks like the engine room did everything four minutes before it was asked to.
He has queried it once. I showed him the clock. He watched it for the stretch, with his own watch, and saw what I see, and he wrote in his report that the engine room clock exhibited a transient deviation and should be monitored, and it is.
The four minutes.
I asked a man who knows the route, an old master, retired, whether four minutes meant anything on that stretch of water.
He said the evening crossing used to leave four minutes earlier, before the timetable changed in the nineties, and that the old ship on the route, on the old schedule, would have been on that stretch at the same clock time my clock shows, and that the old ship's engine room had a clock in the same place on the bulkhead as mine, and that he had stood beside it.
What is done about it.
The engine log carries a note on the evening crossing, in my hand, that says clock deviation observed, entries corrected to bridge time, and the corrections are made in red, four minutes, on every entry on the stretch, every evening, for as long as I have been chief.
What I do.
I keep the engine room.
The one thing I have changed is that I make the log entries on that stretch from the bridge clock, on the intercom, rather than from mine.
The reason is a night in the winter when I was standing at my clock with my watch, as I do, at the point where the drift starts, and the second hand on my clock did not slow, and my watch did not slow, and the difference between them opened anyway, and at about the two minute mark I heard, from the bulkhead behind the clock, where there is nothing but steel and the sea, a second clock, mechanical, ticking, four minutes out of step with mine, and I have not stood there since.