Worked DR to EP: Coordinates and Assumptions

Start from the fictional fix 50°00.0′N 001°00.0′W. The yacht travels on 090°T through the water at 6 kn for two hours with no leeway, so its DR displacement is 12 M east. Near 50°N, one minute of longitude spans approximately cos 50° = 0.643 M. The longitude change is therefore 12 ÷ 0.643 = 18.7′ east.

Moving 18.7′ east from 001°00.0′W reduces the west longitude to 000°41.3′W. The 1400 DR is 50°00.0′N 000°41.3′W. Apply a steady stream setting 180°T at 2 kn for two hours: drift is 4 M south, equal to 4.0′ of latitude. The 1400 EP is 49°56.0′N 000°41.3′W.

The calculation assumes the start was accepted, 090°T and 6 kn were maintained, leeway was negligible, the stream remained representative and the short east-west conversion used an appropriate latitude. Mark and time DR and EP, retain an uncertainty area and compare with depth, visual, radar or checked GNSS evidence before using the result near danger.