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Day Skipper revision module 11 of 17
Tidal heights, tidal curves, tidal diamonds, stream atlases, and secondary port corrections.
8 guided lessons · 16 practice questions · 15 flashcards
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The gravitational effects of the Moon and Sun, together with the motion of the Earth-Moon system, create the main astronomical tide-producing forces. A simple equilibrium-tide diagram wit...
Authority cluster
Around new and full Moon, the tide-producing effects of the Sun and Moon reinforce one another and spring ranges occur. Around first and third quarter, the effects partly oppose one anoth...
Chart Datum is the zero from which charted depths and predicted tidal heights are measured. In areas with an appreciable ocean tide it is usually Lowest Astronomical Tide or a closely rel...
ADMIRALTY Tide Tables provide daily high- and low-water times and heights for standard ports, plus differences and methods for secondary ports. Almanacs and authorised digital services ma...
Start with the relevant high-water time and height and the bracketing low-water height. Calculate range = HW height - LW height. Express the required time as hours before or after high wa...
A charted tidal diamond identifies a position whose table gives set and rate, commonly from six hours before to six hours after high water at a named reference port. Set is the direction...
Standard ports have full daily high- and low-water predictions. A paper tide publication can provide secondary-port differences from a named standard port: separate time corrections for H...
Worked height: HW is 4.9 m at 1200, LW is 1.3 m at 1800, and the supplied curve factor at 1500 is 0.50. Range = 4.9 - 1.3 = 3.6 m. Rise above LW = 3.6 × 0.50 = 1.8 m. Predicted height = 1...
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This independent revision material is not a substitute for current official publications, competent instruction or on-water judgement.