Article by Capt. Steve Katz
Networking
While the calendar has turned a page and the Labor Day holiday just passed marking an eventual change of seasons, thankfully the fishing and the weather remain hot, with anglers and boaters looking forward to less busy waterways and fishing grounds.
The slowdown from the busy summer season can allow anglers time to look forward to their next season; next summer or for some, winter fishing in warmer destinations. This future planning often includes boat maintenance and upgrades.
When it comes to marine electronics and related systems, adding on to an existing system is a popular way to upgrade to new features. Most of these add-on components connect to your existing marine electronics using a network. There are a few popular types of marine networks – NMEA0183, NMEA2000 and Ethernet. These networks are all different and independent and are often required to be present in parallel on a modern boat with multiple marine electronic displays and accessories.
NMEA 0183
The NMEA 0183 Interface Standard is used worldwide across many industry segments. The standard defines electrical signal requirements, data transmission protocol and time, and specific sentence formats for a 4800-baud serial data bus. Each bus may have only one talker but many listeners. This standard is intended to support one-way serial data transmission from a single talker to one or more listeners. This data is in printable ASCII form and may include information such as time, position, speed, water depth, etc.
NMEA0183, while it had been around for many years, it is still commonly used, mostly with VHF radio connectivity and other basic devices.
NMEA 0183 HS (High Speed)
The NMEA 0183-HS standard defines electrical signal requirements, data transmission protocol, and timing for a 38.4K-baud serial data bus.
Each bus shall have only a single TALKER but may have multiple LISTENERs. Specific sentence formats are common to both NMEA 0183 and NMEA 0183-HS and are defined in NMEA 0183.
NMEA 2000® Interface Standard
The most popular standard for serial-data networking of marine electronic devices is the NMEA 2000® standard. This network contains the requirements of a serial data communications to inter-connect marine electronic equipment on vessels. The standard describes a low-cost, moderate capacity, bi-directional, multi-transmitter/multi-receiver instrument network to interconnect marine electronic devices. It is multi-master and self-configuring, and there is no central network controller. Equipment designed to this standard will have the ability to share data, including commands and status with other compatible equipment over a single channel. It is based on CAN (Controller Area Network). All NMEA 2000® products must be certified by the NMEA. The data messages area organized by PGN, “parameter group.” It is a data record containing a Parameter Group Number (PGN) and a set of data fields. The number and meaning of the data fields vary from one PGN to another. Typically, a sensor device sends out PGNs at regular intervals, or when a value changes, and this PGN can then be read by any other device on the network. Some marine electronics manufactures have put their own spin on the NMEA2000 standard and gave it a new name, such as Raymarine’s SeaTalkNG or Simrad’s Simnet. While these re-branded networks are often compatible with NMEA2000, caution should be used with installing a mixed network.
Ethernet
Ethernet is a computer term describing a protocol that allows electronics to talk to each other over wired networks that use shared devices to direct traffic. Ethernet also works seamlessly with wireless protocols, too. Ethernet networks often use common hardware, such as the RJ45 connection and twisted pair wiring. When it comes to marine electronics networks, there are a variety of connectors, cabling and functionality adapted by each manufacturer to make use of Ethernet network. Marine Ethernet networks can carry a lot of information very quickly, typically used for radar images, sounder images, weather data and much more.
OneNet
An upcoming new NMEA standard will incorporate ethernet style high speed data and bandwidth with the stability of NMEA2000 PGN’s, this new standard is called OneNet. The OneNet Standard for IP Networking of Marine Electronic Devices is a marine industry standard, developed by members of NMEA, based on Internet Protocol, Version 6 (IPv6) and IEEE 802.3. OneNet provides a common network infrastructure for marine devices and/or services on IPv6. This allows OneNet to coexist with other protocols and services that operate parallel on the same network, including other marine standards such as IEC 61162-450. Like NMEA 2000, all OneNet products will need to be certified by the product manufacturer and verified by NMEA.
When it comes to your own boat, you may find that your modern marine electronics communicate with many sensors and accessories on-board, often using one or more networks. It is important to learn what is required to add a new piece of hardware but even more important to understand how your existing equipment is interconnected. §
