NavList:

In the beginning, God created the Heavens and the Earth but there was no such thing as "time." Then, very much later, humans invented "time" when the need arose for different people to syncronise their actions, e.g., school teachers were in the school when the students arrived. But all time was local, there was no need to syncronize with people that were far away so every town kept its own solar time, until railroads came along. Then, to keep trains running in opposite directions on the one set of tracks from crashing into each other, trains leaving from different stations which kept their own time and separated in longitude, a system of zone times was created in the 1880's to cure this problem on land.

Prior to the invention of radio there was no need (or ability) at sea to syncronize or coordinate actions on board different ships out of sight of each other or with the shore so each ship kept its own "ship's time," which was local solar time. At the time of the noon sight the captain would command "make it noon" and the ship's clock would be advanced or retarded to 12:00, eight bells would be rung, and the forenoon watch would be relieved. This kept ship's time in synchronization with the only true, natural, universal time, the sun. People ate supper at noon and the watch schedule revolved around that schedule. On a ship traveling at 120 nautical miles per day east or west the solar time will change only eight minutes per day and this eight minute difference is accounted for in the forenoon watch. If the ship is traveling towards the west then the forenoon watch would be 4:08 and if traveling towards the east then the forenoon watch would be on 3:52. Does this mean that the crew members assigned to the forenoon watch reap the benefits if traveling east or get stuck with the penalty if traveling west, no. This is because of the two, two hour dog watches between four p.m. and eight p.m. which cause the watch schedule to rotate every day. If the port watch had the forenoon watch today then the starboard watch would have the forenoon watch tomorrow.

This is still a good system on a slow boat crossing the ocean. There is no reason to keep zone time until you make a radio call for berthing instructions at which point you will need to coordinate with shore facilities that are keeping some form of zone time so at that point it is good to set your clock to the local time, maybe daylight savings time, or an odd offset zone time.

However, for one person aboard, the navigator (after the invention of the chronometer) it was necessary for him to know the time at a different place, the navigator needed Greenwich time for his computations so he let the chronometer run, and didn't reset it during the voyage and made appropriate accommodation for the known rate of the chronometer. 

But now we have 25 time zones, with zone descriptions of plus one though twelve, minus one through twelve, and a zero time zone now known as UT or Zulu time (formerly GMT.)

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