Worked DR and EP from Course, Log, and Tide

Start the DR from the last established position. For the chosen interval, plot the true course steered and the distance run through the water. In the convention used for this lesson, wind and current are not included in the DR; record the time and assumptions so another navigator can reconstruct it.

An EP modifies the DR with additional estimated information that is insufficient by itself to establish a fix. For a supplied tidal stream, calculate drift from rate × time and plot it in the direction of set from the DR endpoint. If leeway is also supplied, represent it consistently in the water-track or vector construction rather than adding the same effect twice.

Plotting symbols differ between training and operational conventions. The USCG handbook, for example, uses a semicircle for DR and a square for EP, while other schemes use different marks for electronic fixes or estimates. Use the convention specified by the course, chart or organisation, and label time and method rather than relying on shape alone.

A neat EP is still an estimate. Steering error, log error, changing stream, leeway and the quality of the starting position all travel with the construction. Near danger, shorten the interval and seek independent position evidence instead of allowing the plot to create false confidence.