In Dreams--Note to myself

[cyrano]

She was a ship of the line, and a time travelling device. I don't know whether they had to be 'ship of the line' class or not, but this one was. The navigator had to take careful readings--the time, longitude and latitude were critical. And if the seas were rough at all, hitting your target could be almost impossible. An unexpected swell could mean missing the target. And given that the ship didn't travel (only the agent), a miscalculation could easily mean the loss of an agent.