Module 11 - Tides & Tidal Streams
Worked Secondary-Port and Tidal-Gate Example
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. Use secondary HW 0550 at 4.8 m and secondary LW 1213 at 1.3 m before using the curve.
The corrected range is 4.8 - 1.3 = 3.5 m. If the tidal curve factor two hours after HW is 0.72 of the fall from HW toward LW, the height is HW - (range x 0.72) = 4.8 - (3.5 x 0.72) = 2.28 m, rounded to about 2.3 m before applying safety margin.
Yachtmaster standard is not just the arithmetic. If the headland gate turns foul at HW +0400, corrected HW 0550 gives a foul-stream start at 0950. A plan to be clear by 0920 gives only a 30-minute margin; the examiner may ask what you will do if boat speed, visibility, or sea state reduces progress.
0535 + 15 min; 5.2 m - 0.4 m
Result: 0550 at 4.8 m
1148 + 25 min; 1.1 m + 0.2 m
Result: 1213 at 1.3 m
4.8 m - 1.3 m
Result: 3.5 m
4.8 - (3.5 x 0.72)
Result: About 2.3 m
0550 + 4 h - 30 min
Result: 0920 with a tight margin
| Step | Calculation | Result |
|---|---|---|
| Secondary HW | 0535 + 15 min; 5.2 m - 0.4 m | 0550 at 4.8 m |
| Secondary LW | 1148 + 25 min; 1.1 m + 0.2 m | 1213 at 1.3 m |
| Range | 4.8 m - 1.3 m | 3.5 m |
| Height two hours after HW | 4.8 - (3.5 x 0.72) | About 2.3 m |
| Gate latest time | 0550 + 4 h - 30 min | 0920 with a tight margin |
Key points
- Correct the standard-port times and heights before using the curve.
- Show whether the tide is rising or falling before choosing add/subtract logic.
- Convert tidal phases into clock times for the passage plan.
- State the contingency if the gate margin starts to disappear.
Continue studying Tides & Tidal Streams
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