What is NMEA 2000 and How Does it Work?

It’s never been easier to build a custom marine electronics system. NMEA 2000 allows your boat’s electronic devices to ‘talk’ to each other and share data through a single cable. It’s ‘plug-and-play’, robust, handles up to fifty devices, and allows you to monitor all of your boat’s systems. It makes boats lighter, more reliable, and easier to control.

What is NMEA 2000?

NMEA 2000 is a marine Industry Open Standard created by the National Marine Electronics Association (NMEA). NMEA is a marine industry trade group made up of marine electronics manufacturers. They work together to enhance marine electronics technology, provide training, and set standards for how marine electronics communicate with each other.

They designed NMEA 2000 with four goals in mind.

  1. Allow marine electronic devices to communicate and share information.
  2. Create a standardized way for electronics to connect to each other.
  3. Verify that products certified as NMEA 2000 meet minimum standards.
  4. Ensure certified devices don’t interfere with other equipment.

How Does NMEA 2000 Work?

Devices certified as NMEA 2000 compliant contain microchips. These chips allow devices to share data with other devices. At the same time, the chip also lets the device receive data from other devices. Devices communicate with each other through a control area network (CAN). CAN allows devices to exchange data without going through a computer or master controller. Devices connect to each other through a set of cables and connectors that are part of the NMEA 2000 standard.

All NMEA 2000 compliant devices must be able to self-configure. What this means is that all the devices connected to the backbone cable organize themselves into a network. This is done automatically. There’s no need to hire a technician to set it up or even connect the system to a computer. Likewise, when you add a new device to the backbone it configures itself to the network.

Additionally, each device must be able to claim an address. The address is much like the URL of a website. It identifies the device as a unique unit.

What Does NMEA 2000 Do?

NMEA 2000 allows marine electronics to communicate with each other and share data. Every electronic device on the network can send and receive data, instructions, and updates to and from every other device. If, for instance, a Chartplotter needs to know the boat’s position it can receive coordinates from a GPS connected to the network.

In addition to sharing information, NMEA 2000 can monitor and control all of your boats onboard systems. Basically, if it runs on electricity, NMEA 2000 can monitor and control it. And, if it doesn’t run on electricity, there’s a sensor that can be used to monitor it as well. For example, NMEA 2000 can monitor batteries, rudder position, AC and DC electrical systems, motors, bow thrusters, awnings, and many other systems. On top of that, you can install sensors that will alert you to problems such as smoke, carbon monoxide, high bilge water, or a circuit going bad.

How Does CAN Work?

NMEA 2000 devices communicate with each other using the Control Area Network (CAN). CAN was developed for the automotive industry in the mid-1980s as a way to control engines, transmissions, and anti-lock braking systems.

CAN is a set of rules that allows devices to share data. With CAN, there is no central controller. Each device is free to send or receive data over the CAN bus. According to Wikipedia a CAN bus is an automotive engineering term that refers to “a specialized internal communications network that interconnects components inside a vehicle “.

When a device has data to send it checks the CAN bus. If the bus is not busy it sends a frame. The frame identifies and sets the priority, data message, source, and destination of the message. If another device is trying to send a frame at the same time the device with the highest priority sends its frame first while the other device waits.

Claiming an Address

When the NMEA 2000 network is turned on, or a new device is added, each device connected to the backbone claims a unique address. If two devices try to claim the same address the device with the higher priority wins out and the other device looks for a new address. As soon as a device has successfully claimed an address it starts to transmit data.

CAN Names

Each device connected to the backbone must have a unique NAME. The NAME is used to determine what devices have priority when claiming an address. The device NAME contains the following information about the device.

  • What the device does and who manufactured it.
  • A number to differentiate it from other devices of the same make and model connected to the backbone.
  • A number to differentiate it from other devices from the same manufacturer.

Parameter Group

Messages that are sent over the network are sorted into a parameter group. These are identified by a parameter group number (PGN) that is shown in the CAN identifier field. Parameter groups are classified as either address messages or broadcast messages.

Parameter groups are how devices exchange data. Each one contains a data record with one or more fields related to either the device sending the message or to the vessel. When needed, parameter groups repeat at regular intervals.

Parameter groups are sent as CAN frames. Each frame contains 8 bytes of data. When a parameter group contains more than 8 bytes of data, it sends additional CAN frames. Because of this, CAN frames include a CAN identifier field. This field includes the priority of the parameter group, what device sent it, and where it is being sent to. CAN frames are sent to every device connected to the backbone. Devices check the ID and decide to either use the data or ignore it.

nmea 2000 cables
NMEA 2000 Cables
1- Terminating Resistors
2- Backbone Cable
3- Power Tap
4- T-Connector
5- Drop Cable

Are all NMEA 2000 Connectors the Same?

NMEA 2000 uses a single backbone cable that connects everything together. Electronics, electrical equipment, and sensors all connect to the backbone cable through Drop Cables and T-connectors. The system draws power through a Power Tap wired to a fuse or circuit breaker.

Backbone Cable

A Backbone Cable connects all devices in the network together. It comes in different lengths or you can cut it to custom lengths. All NMEA 2000 cables and connectors use standardized male, female screw-down connectors rated to IP67. Cables come in 3 different sizes.

  1. Mini: 0.41-0.49 ” diameter, carries 8 amps of current, used for backbone or drop line.
  2. Mid: 0.33″ diameter, carries 4 amps of current, used for backbone or drop line.
  3. Micro: 0.24-0.28″ diameter it is usually used as a drop line because of greater flexibility.

T-Connectors

T-Connectors are inserted between sections of the Backbone Cable. They connect an electronic device, sensor, or piece of electrical equipment to the network through a Drop Line. T-Connectors make adding new electronics to the system quick and easy. Place a T-Connector between two sections of Backbone Cable, add a Drop Line to the bottom of the T, then connect the other end of the Drop Line to the electronic device, sensor, or electrical hardware you want to add to the network.

Terminating Resistors

A terminating resistor must be placed at either end of the backbone cable. The purpose of the resistors is to reduce disturbances in the network when a device is disconnected from the network.

Does NMEA 2000 Need Power?

Yes, the NMEA 2000 backbone cable draws power through a Power Tap. One end of the Power Tap connects to a fuse or breaker the other to a special T-Connector. Connect power as close to the center of the backbone as possible. Doing so will ensure even power distribution throughout the system.

However, the backbone cable is only able to power devices that draw up to 1 amp. Any device needing more than 1 amp of current must be wired to its own power source. Fortunately, NMEA 2000 certified devices show how much current they draw from the backbone cable on the label. The current draw is shown as a Load Equivalence Number (LEN). One LEN is equal to 50mA draw by the device. In other words, a device drawing between 51mA and 100mA has a LEN of 2, 451mA – 500mA (.5A) a LEN of 10, and so on until it reaches 1000mA or 1 Amp.

digital switching

NMEA 2000 + Digital Switching

Digital Switching replaces switch pannels and circuit breakers with digital control modules. These control modules are used to power and control all of your boat’s electronics and electrical systems. A switch, keypad, digital display, or multifunction display connects to the control module through the NMEA 2000 network or other connectors. The boat’s electronics and electrical devices are then connected to the control module. The control module includes digital circuit breakers to protect your equipment.

Digital switching simplifies installation and greatly reduces the number of wires running through your boat. It is flexible, expandable, reduces weight, and increases reliability. Best of all, it’s programable and gives you access to all the features NMEA 2000 has to offer.

Types of Digital Switches

  • Mechanical Switches: Mechanical switches include momentary switches and two-position switches. Most often, these are rocker switches or pushbutton switches. With these, you have control of the devices but get little feedback on its state. Mechanical switches are best for simple devices such as lighting, livewell, and horn.
  • Keypads: Keypads give greater control than switches. However, like switches you get a limited amount of feedback on the state of the device. They are best for controlling electrical devices that don’t transmit data such as lighting, livewells, and stereo. They can also be used to monitor critical functions such as battery level and bilge. Some keypads let you control multiple devices through a single switch.
  • Digital Displays: Digital displays are used to display critical information that is needed at a moment’s notice. These are often used in place of engine gauges but can also be used for an electronic compass, depth finder, or other electronics. Additionally, digital displays can set alarms to sound in case of trouble such ad an engine overheating or a drop in battery voltage.
  • Multifunction Displays (MFD): MFDs let you access data from all of your boat’s electronic devices from a central location.

In Conclusion

NMEA 2000 makes it possible for marine electronics to communicate and share information with each other. Additionally, it makes installing electronics and electrical equipment easier and more reliable. It eliminates much of the wiring on a boat and can be used to control and monitor almost all of your boat’s electronic and electrical systems. When combined with digital switching, NMEA 2000 allows even you to automate much of your boat’s systems.

In my next post, I’ll go into more detail about digital switching and how to take advantage of it on your boat. Make sure you don’t miss it by subscribing to my feed. Also, if you found this post helpful, please share it on your favorite social media site.