NMEA — your boat's own readings in the logbook
The Logbook app fetches weather data from the internet — convenient, but it describes the region, not your boat. An NMEA connection changes that: the logbook then holds the values your own instruments measured at that exact moment.
What you get from it
The difference shows in every entry. Instead of “wind from the west, 4 Beaufort according to the weather model”, it says what your masthead anemometer really shows — including gusts, wind shadow from land and everything a model cannot know.
- Wind: direction and speed from your sensor, always converted to true wind
- Depth: with an adjustable offset, so the real depth and not just the depth below keel ends up in the log
- Speed and heading through the water — from which the app also calculates set and drift
- Water temperature, log reading and GPS position including accuracy
What you need for it
A standard NMEA-to-WiFi converter is enough — often called an “NMEA to WiFi” gateway. It sits on your boat's NMEA bus and provides the data over WiFi, via TCP or UDP. There are devices for NMEA 0183, NMEA 2000 and SeaTalk; prices range from an inexpensive stick to a full multiplexer.
In the app settings you enter the IP address and port of the gateway and connect — after that everything runs automatically. For Android users it is handy if the gateway can join an existing on-board WiFi network.
The app evaluates the received data regardless of the manufacturer. There is one restriction with Raymarine: the built-in WiFi of current devices speaks a proprietary protocol that only Raymarine apps understand. A separate NMEA or SeaTalk-to-WiFi converter solves this.
Good to know
Apple does not allow NMEA data streams to be received in the background: as soon as the app is off screen — including when the device is locked — the connection is closed. That is why the app disables auto-lock while an NMEA stream is active. You can turn the display down to minimum brightness, but you should not lock it.
Technically the app processes the sentences RMC, MWV, VHW, DPT, MTW, VLW and GGA. Which device delivers them does not matter — the app evaluates the sentence regardless of the sender.