NETWORKING

The National Marine Electronics Association (NMEA) sets the standards for marine electronics networks. The best known is NMEA0183, which has been in existence for more than 20 years. Under this protocol devices communicate with each other by sending and receiving data “sentences.” Some devices are “talkers”and send data (for instance a GPS antenna), others are “listeners,” and still others can both talk and listen. When there are too many interconnected devices, the signals can become diluted and the network can become overwhelmed. It also relies heavily on crimp and other connectors, which are prime sources of trouble.

NMEA0183 has been phased out by most instrument makers, who have adopted the NMEA2000 (N2K) protocol. This not only sends and receives data 50 times faster, but allows many more devices—including those from different manufacturers—to be interconnected. An N2K network consists of a backbone cable into which you plug each device. The connectors are molded, eliminating the poor-connection scenario, and installation is much less complicated.

Some makers have come up with proprietary networking systems—Raymarine has Seatalk NG and B&G/ Simrad/Lowrance use SimNet—which are compatible with others via adaptors, while others use standard N2Kcabling and connectors.

Raymarine’s cables are color coded—blue and white for backbone, black and white for the spur cables— and are available in various lengths up to 30ft. The latter can be daisychained; the instruments I installed came with short lengths of spur cable. It is important to measure well because the cables and connectors are pricey and the cost soon adds up.

I used one five-way connector, to which I ran the power supply. With some trial and error I was able to integrate the various spur cables running to various parts of the boat into the backbone cable.