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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 Mercator turned on its side, good for narrow north-south areas
The cylinder is rotated so it touches a chosen central meridian rather than the equator, giving minimal distortion in a north-south strip a few degrees wide. It underpins the Universal Transverse Mercator grid and national systems such as the Ordnance Survey National Grid, and it is used for large scale harbour and coastal charts in higher latitudes where standard Mercator scale distortion would be objectionable. Rhumb lines are no longer straight, but over a single sheet the difference is negligible.
Read definition →Adding up several short legs mathematically to find one net movement
When a vessel sails a series of short courses, as when tacking, each leg is resolved into northerly and easterly components using departure equals distance times sine of course and difference of latitude equals distance times cosine of course. Summing the signed components gives the net difference of latitude and total departure, from which a single equivalent course and distance follow. Departure is converted to difference of longitude by dividing by the cosine of the mean latitude.
Read definition →Single masthead lantern combining sidelights and sternlight on small yachts
A sailing vessel of less than 20 metres may combine her red, green and white lights in one lantern carried at or near the top of the mast, keeping the standard arcs of 112.5, 112.5 and 135 degrees. Height gives excellent range offshore for very little current draw. It must never be shown together with deck-level sidelights, nor when the engine is driving the boat, and it is less useful inshore against shore lighting.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.