Estimated position from current set & drift

Bowditch Ch. 1 §102

Bowditch Ch. 1 §102 — Introduction to Marine Navigation Dead reckoning (DR) is the determination of position by applying course steered and distance run from a known starting point. DR accuracy degrades over time and must be confirmed by external fixes whenever possible.

Bowditch Ch. 23 §2302

Bowditch Ch. 23 §2302 — Navigational Errors Set and drift describe the effect of current on the vessel's track. Set is the direction toward which the current is flowing; drift is the speed of the current. The vector sum of the intended course (course made good through water) and the current vector gives the actual course over ground.

Bowditch Ch. 24 §2401

Bowditch Ch. 24 §2401 — Currents Surface ocean currents are driven primarily by wind, with major gyres in each ocean basin. Tidal currents are driven by tide rather than wind and reverse direction with the tide.

Bowditch Ch. 24 §2402

Bowditch Ch. 24 §2402 — Currents The vector triangle for current correction is: course steered + drift vector = course made good. Inverting it: from course made good and drift, derive the course steered required to make a given track over ground.

Bowditch Ch. 8 §801

Bowditch Ch. 8 §801 — Dead Reckoning A dead-reckoning (DR) plot projects the vessel's position from the last fix using only course steered and distance run through the water, ignoring current and leeway. A new DR position is plotted at every course change, at every speed change, at the time of each fix, and at least once each hour — more often in pilot waters.

Bowditch Ch. 8 §802

Bowditch Ch. 8 §802 — Dead Reckoning DR plotting symbols are standardised: a fix is a dot inside a circle, a DR position a dot with a semicircle, and an estimated position a dot inside a square. The course line carries the true course as "C 090" above it and the speed as "S 8" below, and each position is labelled with the 24-hour time. Consistent labelling lets any watchstander read the plot at a glance.