NMEA 2000 Vs. NMEA0183
If your vessel is using nmea 0183 there will come a time that you will have the need to upgrade the way your systems communicate with one another through a data network. For the past 25 years or so, we have been using different versions of NMEA 0183 to pass these communications between equipment. About 5 years ago, NMEA2000 was on the market. Picture this, instead of having many wire feeds and daisy chains from one piece of equipment to another, picture only one. Essentially like a backbone. Each end gets terminated and a power feed is added. Equipment is then added to this “backbone” through “Tee” connectors very similar to the plumbing in your house. The backbone also provides power to the unit unless it requires its own dedicated power supply. Although the demonstration below looks simple, it’s design needs to be handled by someone with extensive knowledge in nmea2000 network structure to balance load equivalents and facilitate design to fullest capability for the present devices and possible future ones. The data passes from one unit to the other and if one piece malfunctions or is taken out, the rest of the network still functions independently. In the past you lost one piece and the network would crash until you manually bypassed through rewiring or fixed the unit.
NMEA 0183 Communications
• NMEA 0183 introduced in 1983
• NMEA 0183 single talker, multi-listener
• NMEA 0183 not a network (point to point communication)
• Results in very complex wiring systems
NMEA 0183 is Outdated
• Communication Speed – 4800 baud or bits per second
– (A Seldom used version high-speed 0183 is 38,400 baud)
• Typical 0183 message is 400 bits in size
– Result – NMEA 0183 is limited to 12 messages per second
• Compass: (requires 15 messages per second)
» Heading 10 messages per second,
» rate of turn 4 messages per second,
» vessel attitude 1 per second
• Now consider Compass, GPS, Wind, Depth, Speed, Temp,
AIS, etc.
• Message requirement climbs to more than 100/second
• Very simply NMEA 0183 can’t handle this volume of traffic
Other NMEA 0183 Short Comings
• Cable and connectors aren’t specified
– Therefore Plug-n-play impossible
» (each manufacturer uses different connectors)
• No standardization of wire color coding
– Reliability compromised as connection methods not specified,
corrosion due to poor wiring practices are common place
• Although NMEA 0183 is a standard, no certification process
– Standard is implemented differently by various engineers
» Leads to many interoperability issues (manufacturer A wont talk to
manufacturer B equipment)
• Ambiguities within NMEA 0183 Standard
– Messages can be transmitted in one of several different sentences
leading to interoperability problems between different manufacturers’
NMEA 2000® Because:
•NMEA 0183 Short-Comings
– Point-to-point – complex wiring
– No physical layer specified – plug-n-play impossible
– No real-time data sharing between multiple equipment
– Lack of bandwidth for today’s digital world
– No certification process – interoperability issues
– Interpretation ambiguities leads to interoperability
•Ethernet protocols Short-Comings
– Not suitable real time control applications
– Costly for simple sensors (i.e., temperature, voltage, etc.)
– More power consumption than CAN
NMEA 2000® Beginnings
• NMEA 2000® has been in process of development since 1994
• Industry developed by 40 marine companies & organizations
• Development aided and guided by US Coast Guard,
Oklahoma State University, Sun Microsystems
• Developed in cooperation with:
– Society of Automotive Engineers (Truck and Bus J1939)
– Agriculture and Forestry organizations (Off-road Vehicles)
– IEC and ISO (Global Organizations)
NMEA 2000® Original Objectives
• Network standard –
» data streaming around boat being shared amongst various components
• Facilitate real time control and command status information
» Navigation Information (time, position, speed, heading, variation, rate of
turn, set/drift, depth, waypoint, ETA, distance log, etc.)
» Autopilot control and status (rudder command, rudder angle, cross track
error, radius turn order, etc.)
» Drive-by-Wire Functions (electronic steering, throttle, shifting)
» Engine/Transmission Monitoring (RPM, temperatures, pressures, voltages,
fuel rates, trim, etc.)
» Vessel Monitoring System (pitch, roll, tank levels, batteries)
» Electrical system control and status (DC/AC load switching and status)
» Automatic Identification System (vessel data transmission and status
reporting)
» Environmental Information (wind speed and direction, temperature,
humidity, barometric pressure, sea temp, tide, current, salinity, etc.)
NMEA 2000 Objectives (Cont.)
• Bandwidth to accommodate future needs
• Specify physical layer (cable/connectors)
» To ensure plug-n-play compatibility
• Product certification
» To reduce/eliminate out-of-box interoperability
» Auto-addressing eliminating specialist to install
• Cost effective to implement
» Limiting price increases
• Time determinate
» Protect mission-critical data delivery
• Fail Safe and/or Redundant Capability
NMEA 2000® Based on CAN
• Controller Area Network (CAN) platform for NMEA 2000®
– CAN: high-integrity serial data communications bus for real-time
applications
– CAN has excellent error detection and confinement capabilities
– CAN operates at data rates of up to 1 Megabits per second
– CAN originally developed for automotive
» now used by aerospace, industrial automation, and other industries for real
time control and status applications
– CAN is an international standard: ISO 11898
NMEA 2000® Messaging
• Many industry groups use CAN platform and create their own
messaging
– Bus, truck, and agricultural industries created messaging standard
called J1939 (Used by marine engines)
– Industrial automation industry created messaging called DeviceNet
– NMEA (marine electronics industry) created messaging called NMEA
2000®
• NMEA 2000 currently has over 100 message types for
exchanging information (And is growing)
– Position, heading, AIS, radar tracked targets, waypoints, cross track
error, engine and transmission status, environmental, tanks, etc.
Physical Interface (Cable and Connectors)
• NMEA 2000® specifies cable/connectors ensuring plug-n-play
• Standardized Waterproof cable
» Data pair independently shielded, power pair independently shielded, plus
overall shield encompassing data and power pairs
» Color coded wires reducing wiring errors
• Standardized waterproof connectors
» Can be submerged in the bilge and still operate
» Keyed contact insuring correct wiring
» Gold plated terminals for reliable connections
» Threaded connectors prevent inadvertent disconnects
• Engineered for Serviceability
» Device can be plugged or unplugged without powering down network
» Device failure or removal of product does not effect rest of network