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Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.
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Rigid flag A replica warning that a diver is down
A vessel engaged in diving operations which cannot display the full lights and shapes of a vessel restricted in her ability to manoeuvre exhibits a rigid replica of the International Code flag A, white and blue swallow-tailed, not less than one metre high, with all-round visibility. It means pass well clear at slow speed. The red flag with a white diagonal stripe is a United States and recreational convention, not a signal under the collision regulations.
Read definition →Getting through the calm belt near the equator as quickly as possible
The Intertropical Convergence Zone separates the two trade wind systems and brings light fluky airs, squalls and heavy rain. Its width and latitude vary seasonally and by longitude, and satellite imagery, forecast files and other vessels' reports are used to find the narrowest section. The usual tactic is to cross close to due south or north on the shortest line, motoring if fuel allows, rather than seeking wind by detouring.
Read definition →Log using sound frequency shift to measure speed over ground
Transmits acoustic beams, typically at several hundred kilohertz to a few megahertz, and measures the frequency shift of returns. In bottom track mode, available while the seabed is within acoustic range, often up to a couple of hundred metres, it gives true speed over ground, and dual-axis units also give athwartships speed at bow and stern for berthing. Beyond bottom track range it switches to water track, measuring speed relative to a layer of water.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.