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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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The total water distance covered since the log was last reset
The fundamental input to dead reckoning, where the DR position is found by laying off the course steered from the last known position for the distance shown by the log. If no log is available it is computed as speed multiplied by time, for instance 5.5 knots for 40 minutes giving 5.5 times 40 divided by 60, that is 3.67 nautical miles. Recording it in the deck log at every fix and course change is essential practice.
Read definition →Books of pre-computed sea distances between ports
Admiralty Distance Tables, published in three volumes as NP 350, give the shortest practicable navigable distance in nautical miles between principal ports, routed through junction points and around continents and through canals rather than as straight great circles. Volume 1 covers the Atlantic and Mediterranean, Volume 2 the Indian Ocean and adjacent seas, Volume 3 the Pacific. They are used for voyage estimating, fuel and provisioning calculations and charter party distance disputes.
Read definition →One high water and one low water each day
Occurs where the diurnal constituents K1 and O1 dominate over M2 and S2, giving a single cycle of period close to 24 hours 50 minutes. Found in parts of the Gulf of Mexico, the South China Sea and sections of the Antarctic coast. The form factor F equals the ratio (K1+O1)/(M2+S2); values above about 3.0 indicate a diurnal regime, and values below about 0.25 a purely semi-diurnal one.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.