Worked DR to EP: Coordinates and Assumptions

Start from a fix at 50°00.0′N 001°00.0′W. Steer 090°T at 6 kn for two hours, with no leeway: the DR displacement is 12 NM east. At latitude 50°N, one minute of longitude spans approximately cos 50° = 0.643 NM, so 12 NM east is 12 ÷ 0.643 = 18.7 minutes of longitude. The DR is therefore 50°00.0′N 000°41.3′W.

Apply a steady tidal stream setting 180°T at 2 kn for two hours. Its drift is 4 NM south, equal to 4 minutes of latitude. The EP is 49°56.0′N 000°41.3′W. This example assumes the course and speed were held, the tidal stream stayed representative, leeway was negligible, and the short east-west distance can be converted at the stated latitude.

The EP remains an estimate, not a fix. Mark and time both the DR and EP, retain an uncertainty allowance, compare the result with depth, visual, radar, or GNSS evidence, and obtain a fresh independent fix whenever practical—especially near danger.