Estimated Position (EP)
A DR position adjusted for estimated set and drift; it remains an estimate rather than an observed fix.
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In depth#
How this term is used in the rules, and where it tends to trip people up on the exam.
From dead reckoning to an estimated position
Start at the DR position for the observation time. Calculate the current's displacement from its set, drift, and elapsed time, then lay that vector off from the DR position. Its endpoint is the estimated position, conventionally plotted as a dot inside a square.
An EP is still an estimate
An EP corrects the DR track for an estimated current; it is not a fix based on observed lines of position. Between fixes, Bowditch treats it as the best available position when only the current can be estimated. Obtain and plot a new fix whenever reliable observations are available.
Exam questions#
What is the difference between an EP and a fix?
An EP adjusts a calculated DR position for estimated set and drift. A fix determines position from observations, so it does not rely only on the estimated current correction.
How is an estimated position marked on a chart?
Plot it as a dot inside a square and label it with the time.
Sources#
- NGA Pub. No. 9 — The American Practical Navigator, Vol. I, §803 (retrieved 2026-08-09)
Related terms#
See Estimated Position (EP) in a real exam question.
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