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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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A sextant angle limit that warns you are approaching a hazard
A pre-computed vertical or horizontal sextant angle sets a boundary. For a vertical danger angle, the angle to a lighthouse of known height increases as the vessel closes; keeping the observed angle less than the pre-set value keeps the vessel outside a circle around the danger. Horizontal danger angles between two marks work identically, the angle growing as the vessel approaches. Both give continuous warning without plotting and remain valid regardless of compass error.
Read definition →The worse half of a tropical storm, where wind pushes you inward
The half of a revolving storm on the side where the storm's forward motion adds to its circulating wind, and where the wind tends to blow a vessel into the track ahead. It is the right-hand semicircle relative to the direction of travel in the Northern Hemisphere and the left-hand in the Southern. The opposite half is the navigable semicircle, in which running with the wind on the appropriate quarter takes a vessel clear.
Read definition →The correction printed on a chart to move satellite positions onto it
Charts not compiled on WGS84 carry a caution giving the adjustment in seconds or fractions of a minute of latitude and longitude to be applied to satellite-derived positions before plotting. The shift is stated with its direction, for example positions should be moved 0.05 minutes south and 0.09 minutes east. Where the survey is old or the shift is unquantified, the note may instead warn that the shift cannot be determined, and the chart must then be used with extra caution.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.