Abbreviation | General Nautical Terminology | Nautical Topics | Depths & Clearance | Navigation | Tides
Low Water (LW)
The lowest level reached by the tide during a particular tidal cycle.
Tides
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Abbreviation | General Nautical Terminology | Nautical Topics | Depths & Clearance | Navigation | Tides
High Water (HW)
The highest level reached by the tide during a particular tidal cycle.
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Astronomical Tide
The component of sea-level change predicted from the gravitational effects and motions of the Moon, Sun and Earth. Harmonic predictions describe this regular component for a location. Actual water levels may differ because of atmospheric pressure, wind, waves, river flow and other meteorological or oceanographic effects.
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Tide-generating Force
The differential gravitational effect that produces tidal deformation of the oceans and Earth. It arises because the Moon’s and Sun’s gravitational attraction and the motion of the Earth–Moon system vary across the Earth. The lunar effect is generally stronger, while the relative alignment of Sun, Moon and Earth produces the spring–neap cycle.
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Tidal Vector
A vector representing the direction and rate of a tidal stream for a stated time and place. On a passage plot it is combined with the vessel’s through-water vector to determine course to steer, ground track or speed over ground. The plotted length must use the same time and scale as the other vectors.
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Tidal Residual
The difference between an observed water level or current and the value predicted from astronomical tides. Residuals arise from meteorological effects, river flow, modelling limitations and other non-tidal influences. They can materially alter available depth and tidal-stream timing, particularly during strong winds or abnormal atmospheric pressure.
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Tidal Datum
A reference level derived from tidal observations and used for tidal heights or coastal elevations. Examples include mean high water and mean low water, while chart datum is selected for charted depths and predicted tide heights. A tidal datum is local to a place and epoch and must not be confused with a land-survey vertical…
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Coriolis Effect
The apparent deflection of motion relative to a rotating reference frame, including Earth. On Earth, freely moving air and water are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The effect is zero at the equator and increases with latitude and speed. It strongly influences large-scale winds,…
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Ferry Gliding
A technique for crossing flowing water by pointing the vessel into the stream so the current carries it sideways across the channel. The vessel maintains steerage through the water while its upstream heading and the current combine to produce a ground track across the flow. Adjusting the ferry angle changes sideways progress and upstream or…
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Syzygy
A near-straight alignment of three celestial bodies, such as the Sun, Earth and Moon at new or full moon. In the Earth–Moon–Sun system, syzygy combines lunar and solar tide-generating forces and is associated with spring tides, which have a greater-than-average tidal range. Exact local tides remain shaped by basin geometry, depth and weather. Syzygy is…
If you belive the Earth is flat, you're about to fall of the end...
If you belive the Earth is flat, you're about to fall of the end...
