Glossary

NMEA 2000

Also N2K

What is NMEA 2000?

Standardised bus system for navigation and engine data on board. Chartplotter, log, wind instrument, autopilot and engine interfaces exchange messages with defined identifiers on it.

What matters about NMEA 2000 in practice?

It uses the same M12 connector system as the P-Bus, but is a separate, certified network. The two networks may only be coupled via a bridge; the fact that a connector fits is no approval.

Each side keeps its own termination. The bridge is a normal node on both networks via a T-piece and does not replace a terminating resistor.

How is an NMEA 2000 network built?

  • A continuous main cable, the backbone, with a terminating resistor at each end.
  • Devices connect to the backbone via T-pieces and short drop cables.
  • The network is supplied with 12 V and fused at one point, in long networks preferably in the middle.

What does the LEN rating mean?

LEN stands for Load Equivalency Number and describes a device’s current draw from the network; 1 LEN equals 50 mA. The total of all devices determines whether cable size and power feed are sufficient.

Which data run over NMEA 2000?

Navigation, wind, depth and engine data, but also battery and tank values. The chartplotter can then show, for example, state of charge and tank levels that a monitor such as the BTM2 puts on the network.

Related terms

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