Fix Interval and Frequency

Definition

Fix frequency should be short enough that the vessel cannot reach a charted danger between fixes, allowing for the largest plausible positional error. Offshore in open water, hourly or two-hourly fixes suffice. In coastal waters ten to twenty minutes is usual, and in pilotage waters continuous visual monitoring by transits, clearing bearings and sectored lights replaces discrete plotting altogether. The interval is a passage-planning decision recorded before departure, not an improvisation at the time.