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Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.
Page 15 of 22
A fix from a radar target's measured distance and direction
Radar measures range far more accurately than bearing, typically to within about one percent of range scale, while bearing error can be one or two degrees because of horizontal beamwidth. The preferred practice is therefore to fix from two or three radar ranges to well-defined isolated features, plotting arcs, rather than relying on a radar bearing. A single range plus a visual bearing of the same object is a common and sound compromise near the coast.
Read definition →Overnight land fog that can drift out over harbours at dawn
Forms over land on clear, calm nights when the ground radiates heat, chilling the air near the surface below its dew point. It does not form over the open sea, but it drifts down rivers and estuaries on a light land breeze and can blanket harbour approaches around sunrise. Moderate wind or daytime heating disperses it, so it usually clears by mid-morning in summer but may persist all day in winter.
Read definition →Crossing bearings taken by radio to shore transmitters or beacons
A fix from bearings of radio transmitters obtained with a direction finding receiver and loop or crossed loop aerial, plotted like visual bearings after applying quadrantal error correction and, over long distances, half convergency. Accuracy is modest, commonly a few degrees, and degrades badly at dawn and dusk through sky wave effects and near coastlines through refraction, so it is treated as an approximate position only. Largely superseded by satellite systems but retained conceptually for homing on distress transmissions and emergency beacons.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.