Documentation

Getting started

NauticCalc runs on iOS 17.6 and later and bundles over 31 tools across thematic areas — navigation, calculators, marine and logbook.

Offline, all core calculations, the logbook and GPS tracking work on your device without internet.

Live weather, worldwide online tides and the plain-text briefing need a data connection plus your own API keys from the respective providers (see the next section).

API keys for live data

For live services you can enter your own API keys (bring your own key): Stormglass and OpenWeather for weather, WorldTides for tides worldwide, and an Anthropic key for the plain-text briefing. NauticCalc does not sell a subscription for this — you set quotas directly with the respective provider.

Enter the keys in the app settings. Without keys, all calculators and the logbook remain fully usable; only the live services mentioned above are unavailable. For the plain-text briefing, a compact offline summary remains available without an Anthropic key.

Tides offline and online

Offline tides are based on embedded harmonic constants (XTide harmonics-dwf-free / NOAA National Ocean Service, public domain). Around 1,000 stations are included; the focus is US waters and selected international ports.

For regions without a suitable offline station — including many European cruising grounds — you can switch to live tides with a WorldTides API key. Coverage details are also in the homepage FAQ.

Trip planning and plain-text briefing

In trip planning you draw your route with start, waypoints and destination on the map. For each leg, NauticCalc shows weather, wind, tides, current and daylight, along with smart safety hints — such as an arrival after sunset or a reefing recommendation in strong wind. A trip plan can also be opened directly from a logbook trip; start and destination are carried over.

The plain-text briefing sums up, in one readable paragraph, how wind, swell, current, tide and sun times interact. With your own Anthropic key the AI writes this text; without a key you get a compact offline summary. Important: the AI only phrases, it does not calculate — all values come from the app's nautical calculations.

You can export the finished trip plan as PDF (real A4 pages with a route map), CSV or JSON.

Polar diagram and sail plan

In the boat profile you can store your boat's polar — as a .pol or .csv import, via the cruising-yacht preset, derived from your cruising speed, or by hand in the TWA×TWS grid. The polar assigns a boat speed to every combination of true wind strength and true wind angle.

With a valid polar stored, voyage planning works out the arrival time for each leg from that speed instead of one flat figure, and shows the sail plan (close-hauled, beam reach, broad reach or “motor recommended”). If the course falls in the no-go zone, you get a beating plan instead of an unholdable ETA: tack headings, close-hauled angle, extra distance and sailing time; for a course too deep, a gybing plan. The turning point can be added to the route as a waypoint at the tap of a button.

Onboard instruments over NMEA (beta)

NauticCalc can read live values from the boat network: speed through water, speed and course over ground, apparent wind and depth. NMEA 0183, Signal K and NMEA 2000 (raw) are supported. The values can be carried into the calculators, the logbook and voyage planning at the tap of a button.

This requires an NMEA gateway that puts the instrument data on the onboard Wi-Fi, and an iPhone on that same network; in the app you enter host and port. On the first connection attempt iOS asks for local network permission. The connection stays local — no instrument data leaves the device.

The feature is marked as beta and is being switched on gradually; it needs app version 1.7.0 or later.

Logbook, ship's kitty and export

The logbook records events automatically and manages crew and watches as well as vessels and trips; the weather can be attached to each entry. The ship's kitty adds an expense tracker for charter crews: record expenses, calculate shares and settle up fairly at the end.

All passage, logbook and ship's-kitty data are stored only on your device; we do not run a central server or cloud sync.

You can export data at any time — for example as CSV, JSON or PDF (logbook as well as the kitty settlement).

Calculators and magnetic field

NauticCalc bundles recognised nautical calculators — including current triangle, course correction (true ↔ compass heading), variation using the WMM2025 geomagnetic model (NOAA NCEI / British Geological Survey, public domain), apparent wind, ETA, light dipping below the horizon and taffrail log, plus unit converters for length, speed, temperature, depth and wind force.

NauticCalc is an aid for skippers and does not replace certified navigation equipment, official procedures or independent navigation decisions on the water.

Usage and shortcuts

HowTo guides with clear steps are in the guides overview — from variation and course correction to tide keys, logbook export and anchor alarm.

For quick answers, see the homepage FAQ as well.