Celestial navigation and dead reckoning, in one piece of software.

Position, date, and observation settings

Latitude, longitude, height of eye, horizon type (natural, artificial bubble or reflecting, dip short), temperature and pressure correction, index error, limb observed for the Sun and Moon. Position can be frozen, and UTC date/time entered with a local offset.

Three interface levels (including "Expert", shown here) adjust the density of the fields displayed to your level of practice.

GHA, declination and altitude for every body, at any instant

Sun, Moon, all eight planets and the First Point of Aries (GHA Aries) computed simultaneously, with apparent horizontal positions (altitude, azimuth, zenith distance). Sunrise, sunset, meridian passage, civil dawn and dusk computed for the entered position. Compass check by azimuth/amplitude and local circumstances of a solar eclipse are included.

Which bodies to shoot, and when

At nautical dawn or dusk — or at any given time — the software lists every body above a minimum altitude, with altitude and azimuth computed, and suggests a set of 3 to 4 well-spread bodies for a robust fix (plus a warning when Venus is visible to the naked eye in broad daylight).

From sextant altitude to a fix plotted on the chart

Enter up to 4 observations (body, UTC time, sextant altitude): the program computes the calculated altitude, the intercept and the azimuth for each line of position, solves the fix by least squares, reports the RMS residual, and plots the lines on a chart with automatic or fixed scale — with an automatic warning when the geometry is degraded (lines too nearly parallel). Running fix and running fix by bearings are also available, along with an NP401/HO249 reduction worksheet and SVG export.

Identify a body at a glance

Rectangular sky chart or circular planisphere, with all 88 constellations plotted (IAU figures, d3-celestial/Stellarium data under a BSD licence), background stars, Sun/Moon/planets positioned live, time animation of the sky, and a tool to identify a body from its coordinates.

Plan a route, see it on the chart

Multi-leg route planning, leg by leg, in great-circle or rhumb-line, with course, cumulative distance and estimated duration at the entered average speed; GPX export. The Map tab overlays current position, GPS track, calculated route, dead-reckoning position and last observed fix on a worldwide Natural Earth basemap.

Plug into your onboard electronics

Live GPS reception over serial port (NMEA 0183), UDP network (NMEA 0183 multiplexer), NMEA 2000 (fast-packet frames) or SignalK/WebSocket, with direct position capture in the Observer tab. A built-in GPS simulator can emit these same protocols to test reception, with no hardware required.

Worldwide tide prediction, fully offline

Harmonic calculation computed directly from constants embedded in the software — no connection required — for a catalog of 4,170 stations (source: TICON-4, DGFI-TUM/GESLA-4, CC BY 4.0 licence, via the Neaps database). Monthly table of high and low tides, tide curve for the day, secondary-port corrections, station search by map, dedicated printing.

MOB, error budget, and a tamper-evident logbook

The MOB button (reachable from any tab) instantly marks position and time, then continuously displays the bearing and distance to return — from a live GPS fix when available, or from the entered position with a staleness warning otherwise. An error budget documents the expected precision of the fix, and every line of position is recorded in a logbook chained by SHA-256 hashing, guaranteeing it hasn't been altered after the fact.

An onboard calculator, a glossary, and a full manual

A deck-unit converter (distance, speed, depth, angle, wind, pressure, temperature, volume, mass) and an engine-unit converter (power), instant and nothing saved. The Definitions tab gathers celestial-navigation vocabulary, and the Help tab holds the full manual, printable, with a collapsible table of contents and keyword search.