Coastal Skipper revision module 11 of 17
Tidal heights, tidal curves, tidal diamonds, stream atlases, and secondary port corrections.
11 guided lessons · 24 practice questions · 19 flashcards
A self-guided revision companion that explains essential concepts, then helps you practise and test them. It supports—but does not replace—recognised instruction, practical training, assessment or certification. Access is a one-time payment, not a subscription.
Use this module hub to choose the right lesson, then open the dedicated lesson page for the complete explanation, worked examples, FAQs, and practice questions.
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...
Most ports are listed as secondary ports, with differences applied to a nearby standard port. The almanac provides time differences (e.g., HW is 20 minutes later) and height differences o...
The simple six-hour tidal curve is only a model. Local geography can create tidal anomalies such as double high waters, prolonged tidal stands, rapid rises after a slow start, tidal bores...
Predicted tide data should be checked against what the water is actually doing whenever practical. Some harbours, estuaries, and offshore sites provide tidal observation buoys, current me...
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...
Tidal streams directly affect your course made good, speed over ground, and passage time. On a coastal passage, timing your departure to work with the tide can save hours — or avoid a dan...
Worked secondary-port example: the standard port HW is 0535 at 5.2 m and LW is 1148 at 1.1 m. The secondary port differences are HW +0015 and height -0.4 m; LW +0025 and height +0.2 m. Us...
Add the complete practice layer
Keep reading the public lesson articles, and add this module's guided flow, quizzes, spaced-repetition flashcards, progress, and mock exams with one payment.