I was flying back to Iceland yesterday and since they didn’t want to give me any headphones and normal ones don’t work I was pretty much stuck with playing with the flight-information on the touch screen in front of me. As I was doing that I noticed that the screen suddenly jumped an hour when we were up in the air, supposedly when we passed a time zone line and that got me thinking about the following question:
Do sailors on those big ocean going vessels change their clocks when they pass into a new time zone? Let’s for example think of a big container ship that goes from Japan to Germany; would they always go on local time?
ETA: I seem to remember that the US Navy always acts on Zulu Time, so if that’s true, my question is mostly about civilian vessels.
AFAIK, in the open ocean (outside territorial waters), the time zones are defined in 15-degree slices of longitude, with each hour centred on the relevant meridian, so, for instance, the GMT zone extends from 7.5ºW to 7.5ºE, the GMT+1 zone from 7.5ºE to 22.5ºE, and so on.
I’m not quite sure what that last part means, as I thought the International Date Line was the 180º meridian, except in territorial waters where it follows the boundaries, keeping nations all in one day.
Hmm… then it would be pretty darn neat to time your “shifts” to correspond with time zone changes, so you always get an hour less of work, if you’re going to the east.
On merchant ships normally the time changes on the 12-4 AM watch. It is posted the day before. I do not know if it is done before crossing or after, ya would have to ask a deckie.
Back in the mid 20th century, I made several long sea voyages between Australia and Europe. (It was a time when air travel was relatively more expensive than it is now, so most long journeys were by sea). As several have said, on some days they would announce that the clocks would change on the next day, and I assume they changed some time shortly after midnight. (I wsas too young to stay up that late). I also assume that they tried to keep up roughly with the 15 degree zones, but changing the clocks in the middle of the night was more important than being exactly right with those zones. You’d also want to have the time the same as local time when you arrived at your next port – so you might need to change the clocks by 30 minutes if the next port was Adelaide or Bombay.
Things would get a bit strange with the daily schedule if this were the case - breakfast at sunset, for example. Zulu time is used for certain things (like recording the arrival of messages) but, as HtH notes, local time zones are observed.
U.S. submarines at sea often switch to Zulu time (aka GMT). Before going up to periscope depth, you had to check what the local time was to see if it was night or day on the surface.
On a nine day trip to Europe, the ship made an hour change every night for the first five. I had thought it would help me adjust to the time change more readily, but I found five one hour changes harder than a single five hour change. I don’t think they paid any attention to the actual time zones.
