KOURAKU
From celestial latitude to longitude and the chronometer, dead reckoning, chart and compass, tides, and GPS — knowing where you are, by stars and charts, by watching and interacting. An iOS / Android education app.
In each mode, use "Explore" to see the principle, then "Challenge" yourself: measure, find your position, and check your answer. Your progress through 30 stages (6 modes × 5) is kept in the Logbook, and difficulty labels (Beginner, Standard, Advanced) plus a "Start here" mark show you where to begin. Available in 9 languages: Japanese, English, Chinese (Simplified and Traditional), Spanish, Portuguese, Korean, German, and French.
Modules
Celestial Latitude
Take a sextant altitude of Polaris or the Sun and read off your latitude. See how the altitude of a celestial body is your latitude.
Longitude & Chronometer
Find longitude from the time difference to Greenwich — 15° per hour. An accurate clock unlocks the east-west at sea.
Dead Reckoning
Integrate heading and speed to estimate your position, and watch the current-induced drift error accumulate on the chart.
Chart & Compass
Correct a compass course to true using deviation and variation. Bridge magnetic north to true north on the chart.
Tides
Spring and neap tides from the Moon and Sun. Move a 24-hour tide curve and read the link between celestial positions and the rise and fall of the sea.
GPS Positioning
Trilateration from satellite ranges narrows your position; the 4th satellite resolves the clock error and fixes the point.
Series
Connected to KAIRAKU through tides, currents, and ocean observation. Learn navigation, then the ocean itself.