Longitude was then determined by a chronometer set to Greenwich Mean Time, compared to apparent noon at the ship's current location. The difference in time = the difference in longitude (basically).

While we're at it, I believe that neither the Olympic or Titanic had bow thrusters. Especially in a crowded harbor, if a stiff wind bore directly on the 2+ acres of area that the side of one of those ships presented, a collision was all too likely unless there were tugs standing by. It's easy to forget that a ship moves in a fluid, and does not track like a vehicle on dry land.
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All we can do is all we can do.