Both must be known to plan strategy. The test would see how far the ship could go in a specified time. Slowing or stopping for repairs would count against the ship's performance and reflect poorly on the ship and crew. The best a ship could do, then, was to maintain a constant fairly high speed for the entire time. The test for submarines was to run at a contstant standard speed for 48 hours.
Fog is a common factor off the California coast in winter.
The plan for the engineering run included contingency of turning to seaward in case of running into restricted visibility. The three boats started their runs on the morning of December 17, 1917. The first leg was a run to the south with a course reversal with La Jolla light abeam to port. The engines were direct drive to the screw, giving the boats a speed of about 10 knots. The run south was uneventful throughout the day and as the afternoon wore on, the line abreast was slightly ragged.