Day Skipper training module 11 of 17
Tidal heights, tidal curves, tidal diamonds, stream atlases, and secondary port corrections.
You are preparing a real trip and tidal diamonds and tidal stream atlases changes the decision. Use this module to explain the cue, the risk, and the next safe action before you move on.
8 lesson sections · 16 quiz questions · 15 flashcards
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Tides are caused primarily by the gravitational pull of the Moon (and to a lesser extent the Sun) on the Earth's oceans. As the Earth rotates, bulges of water follow the Moon, creating th...
When the Sun and Moon align (new moon and full moon), their gravitational pulls combine, producing spring tides — the highest highs and lowest lows. When the Sun and Moon are at right ang...
Chart Datum (CD) is the reference level from which depths on charts and tidal heights are measured. It is set at approximately the Lowest Astronomical Tide (LAT) — the lowest tide that ca...
Tide tables list the predicted times and heights of high water (HW) and low water (LW) for standard ports, for every day of the year. They are published in the nautical almanac (or the de...
The Admiralty tidal curve is the standard method for finding the height of tide at any time. Step 1: Find the HW time and height, and LW height, from the tide tables. Step 2: Calculate th...
Tidal diamonds are lettered positions on the chart (e.g., diamond A, B, C) that give the set (direction) and rate (speed) of the tidal stream for each hour relative to HW at a reference p...
Most ports are listed as secondary ports, with differences applied to a standard port. The almanac provides time differences (e.g., HW is 20 minutes later) and height differences or ratio...
Worked height example: HW is 4.9 m at 1200, LW is 1.3 m at 1800, and you need the height at 1500. The range is 4.9 - 1.3 = 3.6 m. 1500 is three hours after HW, so if the curve factor is 0...
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