Harbor Quill Tides

Learn to read a tide curve on twelve invented harbours, driven by a real harmonic model.

Most tide apps hand you a table of times. Harbor Quill Tides hands you the curve itself, and then teaches you how to read it. Every harbour in the app is built from six harmonic waves summed over a mean level, so the shape you see is computed, not looked up.

DRAG THE DAY
The tide screen draws one full day. Drag the time cursor across it and read the height and the rate of rise at any moment you like. High and low water are found by bracketing the rate of change and closing in by halving, and each one is marked in brass on the curve.

THE GATE EXERCISE
A boat of a given draught needs to cross a drying sill with clearance to spare. The app sets the problem and you work out the window. Every exercise is checked by the same solver that draws the answer, so you never meet one that cannot be solved.

SPRINGS AND NEAPS
A thirty day chart shows the range swinging from springs to neaps, and you can watch that cycle emerge from two waves beating against each other rather than being told about it.

THE RULE OF TWELFTHS
The familiar rule of twelfths is drawn straight against the true curve, with the worst gap between them reported in metres. It is a good rule. It is not an exact one, and the app shows you exactly where it drifts.

TWELVE HARBOURS
The twelve invented harbours cover twice daily, mixed and once daily tide shapes, so you can compare a clean semidiurnal port against a mixed or diurnal one side by side. Six lessons each carry a live mini curve drawn by the same engine that draws the main screen.

WHAT IS IN THE APP
- A real harmonic tide model: six constituents summed per harbour, not a lookup table
- Twelve invented harbours across twice daily, mixed and once daily tide shapes
- Draggable day view with height, rate of rise and brass high and low water markers
- Gate exercise: given draught, sill and clearance, find the crossing window
- Fully offline, no ads, no accounts, no permissions - teaching examples only

Five simple screens: Tide, Ports, Month, Learn and How.

Harbor Quill Tides works entirely offline. There is no internet connection, no advertising, no sound, no account and no tracking, and the app asks for no permissions at all.

Important: the harbours in this app are invented for teaching. The numbers are produced by a model, not by a hydrographic survey, and must never be used for navigation. Use official tide tables and charts for any real passage.