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Tide Calculator
Estimate tidal heights using the Rule of Twelfths. Select a reference port, enter hours from high water, and see the predicted tide height and curve.
Parameters
Southampton Data
- MHWS
- 4.5m
- MHWN
- 3.6m
- MLWN
- 1.8m
- MLWS
- 0.5m
Predicted Height
4.50m
Tidal Range
4.0m
Tide State
High Water
Tide Curve (Rule of Twelfths)
Horizontal axis shows hours relative to High Water. The gold marker indicates your selected time.
How the Rule of Twelfths Works
The tide does not rise or fall at a constant rate. The Rule of Twelfths approximates the sinusoidal tidal curve:
1/12
1st hr2/12
2nd hr3/12
3rd hr3/12
4th hr2/12
5th hr1/12
6th hrThis tool uses published tidal levels (MHWS, MHWN, MLWN, MLWS) for each reference port and interpolates between them.
Heights tell you the depth; tidal streams move the boat. Plot a stream as a vector for a DR and EP with the digital Portland plotter.