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Instruments

Connect to onboard marine instruments to display depth, wind, heading, AIS targets, and other sensor data on the chart.

Features

  • NMEA 0183 over TCP — Connect directly to WiFi multiplexers (Yacht Devices, Digital Yacht, Vesper) that broadcast NMEA sentences on the local network. Automatic discovery via mDNS, or manual host and port entry.
  • Signal K integration — Connect to a Signal K server over WebSocket for real-time instrument data. Automatic endpoint discovery via mDNS/Bonjour, or manual URL entry.
  • AIS targets on map — Nearby vessels render on the chart with heading indicators. Tap for vessel details (name, type, speed, course, destination). Data from onboard AIS receivers or online services (AISStream.io).
  • Multiple connections — Connect to several instruments simultaneously (e.g. a Signal K server and a separate NMEA WiFi gateway). Data from all sources merges into the same store.
  • Background operation — Instrument connections stay alive when the app is backgrounded during track recording (piggybacking on the background location session).
  • Automatic reconnection — Lost connections retry with exponential backoff.

Connections

The connections screen (accessible from Settings) shows:

  • Discovered services — Instruments found via mDNS on the local network, with type badges (Signal K or NMEA).
  • Manual add — Enter a Signal K server URL or NMEA host and port directly.
  • Connection status — Each connection shows its current state (disconnected, connecting, connected) and recent data.

Data model

Instrument data uses a flat key-value store with Signal K-compatible paths as keys. All values are in SI units (meters, m/s, radians, Kelvin, decimal degrees). This means:

  • Signal K data flows in without path translation
  • NMEA data gets mapped to the same paths during parsing
  • Components don't care which protocol the data came from
  • Switching from a direct NMEA connection to a Signal K server requires no UI changes

AIS targets are stored separately, keyed by MMSI, with the same path-value structure per vessel. Stale vessels are pruned after a configurable timeout.

Supported data

Data Signal K path NMEA source
Position navigation.position RMC, GGA
Speed over ground navigation.speedOverGround RMC
Course over ground navigation.courseOverGroundTrue RMC
Heading (magnetic) navigation.headingMagnetic HDG
Heading (true) navigation.headingTrue HDG
Depth (transducer) environment.depth.belowTransducer DBT, DPT
Depth (below keel) environment.depth.belowKeel DPT
Apparent wind speed environment.wind.speedApparent MWV
Apparent wind angle environment.wind.angleApparent MWV
Water temperature environment.water.temperature MTW
Speed through water navigation.speedThroughWater VHW

See protocols.md for details on NMEA 0183, NMEA 2000, Signal K, and AIS.