Fix interval

Fix interval is the time the officer of the watch allows to pass between successive position fixes, set short enough that the ship cannot run into danger before the next fix confirms its track. It is a function of speed and the proximity of hazards: in open ocean a fix every hour or half-hour suffices, while in pilotage waters fixes run every three minutes or less, often by parallel index or visual bearings rather than GNSS alone. The passage plan should state the planned fix interval for each leg under SOLAS V/34 voyage-planning practice. A useful rule is that the interval times the speed must stay well inside the margin of safe water.