Let’s say I’m traveling from Southampton to New York on a ocean liner. The ship sails at 1800. Supper is at 2000, I assume Southampton time. The next night, the ship will have crossed a time zone or two. Supper at 2000 then means … “local” time, as it were ( meaning, the time zone the vessel is in)? Or is it 12 hours after the previous supper, meaning we’re still on Southampton time?
Related: do passengers on trans-oceanic voyages have an equivalent to jet lag? Or does the slow journey mean that passengers have plenty of time to adjust?
They adjust the Apparent Time Ship (ATS) nightly. Here’s an event log from the Titanic. Notice how the ATS slips away from where they started as they reset it each night.
I’ve done cruises that have crossed several time zones. They keep a record of ship times, and remind you of changes quite frequently. All scheduled events are according to ship time. They also have clocks that show the current ship time.
Never had a problem with “ship lag”, but of course, I can sleep however long I want! I’m on vacation!
Never been on a ship, but I took a train from Seattle to Chicago in 2023. The switch from Pacific to Mountain time happens well after midnight when the train crosses from Washington into Idaho, so by the time passengers and crew start stirring in the morning everybody is on Mountain time.
The switch to Central time, though, happens in the early evening when the train crosses from Montana into North Dakota, and for onboard purposes they stick with Mountain time for the rest of the day until morning - so your dinner reservation at 7 is Mountain time even if you’re already in ND and it’s now 8 Central.
If a ship goes to another time zone but doesn’t dock, it may keep the passengers’ apparent time in the first zone, or may change it. If you’ll be on land, or are crossing several time zones, you get a nice little card on your bed alerting you to this, and it’s published in the ship’s daily bulletin as well.
On long-distance east/west trains (in both Canada and Australia), we were usually instructed to go back (or forwards) one hour each night at bedtime - no matter where the time zone lines were (and Australia’s 2 1/2 hour jump at the WA border when SA is on DST).
I did a Transatlantic cruise from Southampton to NJ via Vigo, Lisbon, Tenerife, Lanzarote, and Halifax (supposed to be Bermuda but hurricane Tammy diverted us)
We changed time zones several times. There were various notices to set your clock before going to bed. The various video screens changed automatically of course.
Traveling West meant an extra hour sleep on many nights
In 1980 I took the QE2 from New York to France. We lost an hour every night, done in the middle of the night, not when we officially crossed the line between zones.
On a Baltic cruise we also changed zones at night, not when the line was crossed.
Same with me (except we gained an hour each night) when I sailed between Southampton and New York. That was in 1969, but I doubt much has changed on passenger ships.
On ferry journeys between Ireland and France, or Ireland and Spain, the ferry uses Irish time throughout the journey, with no time changes while on board. When the captain announces that we will be docking in Cherbourg at 10:00 am, this means 10:00 am Irish time, with no ambiguity.
The time change happens at 0200 (Dark 2:00). An hour is either added of taken away. If you are on the 12-4 watch it will either be 3 hours long of 5 hours long.