True vs Navigation Almanac

The wind you feel on a moving boat isn't the real wind. True-Wind Calculator turns the apparent wind you measure into the true wind you need — in two taps, no wind instruments required. In use since 2013, completely rebuilt in 2026. HOW IT WORKS Enter boat speed, apparent wind speed, apparent wind angle and heading. The app does exact vector math — no lookup tables, no approximations — and gives you true wind speed and true wind direction instantly. Boat speed and heading can be filled automatically from GPS and compass with one tap. FREE • True wind speed, direction and angle — unlimited calculations • One-tap GPS fill for boat speed and heading • The formula explained, so you can trust the numbers • Works completely offline — no account, no ads, no tracking PRO (one-time purchase, no subscription) • Performance — live VMG, target boat speed, % of target VMG and point of sail, driven by your boat's polar • Tactics — tack preview, windward-mark laylines, and whether you can lay the mark • Boat polars — pick a preset or build your own in the editor • Compass rose view — heading, apparent and true wind on one dial • Calculation history — every result logged with its inputs • All speed units — knots, m/s, km/h, mph Bought the app back when it was paid? Pro is already yours — it unlocks automatically. PRIVACY Everything stays on your device. Location is read only to fill the input fields and never leaves your phone. No analytics, no third-party SDKs.

Navigation Almanac is a complete celestial-navigation toolkit for iPhone and iPad. It reduces a sight, tabulates the almanac data you would otherwise look up on paper, and works entirely offline - no signal, no subscription, no account. SIGHT REDUCTION Enter your position and the date and time in UTC or local time, then pick a body. You get azimuth and computed altitude, GHA, LHA, SHA and declination, semi-diameter and horizontal parallax, along with the magnetic variation from the WMM-2025 model and the current value of ΔT. ALMANAC The Sun, Moon, Venus, Mars, Jupiter and Saturn together with the 57 navigational stars, each with azimuth, altitude, hour angles and declination for the moment you have chosen. RISE, SET AND TWILIGHT Rise, meridian transit and set for any body, with civil and nautical twilight at the Sun's standard altitudes (-0°50′ / -6° / -12°), shown in UTC or local time. SKY VIEW The sky drawn as a chart of azimuth against altitude, or as a full-sky dome with the zenith at the centre. Background stars, constellation lines, and a predicted GNSS satellite layer computed from a bundled orbital catalogue. GPS Live position, course and speed over ground, altitude and horizontal accuracy, the magnetic variation at your position, and the ephemeris of the selected body. One tap fills the observer position for a reduction. COMPASS ERROR Solve gyro and magnetic compass error from an observed bearing, with variation and deviation kept separate, the way the correction is actually applied on the bridge. FIX CALCULATOR Cross two lines of position from your reductions, advance the first line for the vessel's run between sights, and read off the observed position. WORKS OFFLINE The ephemerides are computed on the device from the VSOP87 and ELP2000 series with IAU 1980 nutation - they are not downloaded. Everything above works with the phone in airplane mode, weeks from shore. SIXTEEN LANGUAGES English, Russian, Ukrainian, French, Spanish, Italian, Portuguese, German, Dutch, Polish, Swedish, Danish, Greek, Turkish, Latvian and Simplified Chinese. The navigation terminology in each was taken from that country's own nautical almanac and navigation textbooks rather than translated word for word. NAVIGATIONAL WARNINGS Warnings in force from the national coordinators of the worldwide navigational warning service, grouped by country and by NAVAREA, with the full text of every message and the positions read out of it. The feed is rebuilt every hour and the last copy stays on the device, so it is there when the signal is not. This is an experimental feature and the screen says so: the data is gathered automatically, it can lag behind the broadcast, and it can be incomplete. It does not relieve you of the requirement to receive Maritime Safety Information over NAVTEX and SafetyNET as provided for by SOLAS. Navigation Almanac is a computational aid. Carry the official almanac and tables required for your voyage.