Introduction
NMEA 2000 is a communication standard used in marine electronics to share data between devices such as GPS receivers, depth sounders, autopilot systems, and more. It is based on the Controller Area Network (CAN) protocol, which is a high-speed, low-level communication protocol used in a variety of industries.
One of the main benefits of NMEA 2000 is that it allows multiple devices to share data over a single, standardized network. This makes it easier to integrate different types of marine electronics and allows for more flexibility in terms of what data can be shared and how it can be used.
To use NMEA 2000, devices must be connected to a physical network using special cables and connectors. The network uses a variety of different messages, known as "sentences," to communicate data between devices. These sentences follow a specific format and contain information such as the data type, device address, and the data itself.
NMEA 2000 also includes a number of features to ensure reliable communication, such as error checking and flow control. It also supports the use of "PGNs," or Parameter Group Numbers, which are used to identify specific types of data and allow devices to selectively filter the data they receive.
Overall, NMEA 2000 is a powerful and flexible communication standard that allows marine electronics to work together seamlessly and share a wide range of data. It is widely used in the marine industry and continues to be an important part of modern navigation and communication systems.
LEN
In the context of the NMEA 2000 (NMEA2000) marine communication standard, the load equivalence number, also known as LEN, is the number used to express the amount of current that is used from the NMEA 2000 network.
One LEN is equal to 50mA, and when determining LEN for a device on the network, the current is always rounded up to the next 50mA increment. Example: 56mA would be equal to 2 LEN.
As the NMEA 2000 network is limited to 3 amps, the maximum LEN that can be on a network is 60.
NMEA2000 System Layout
A NMEA2000 systems can be separated into several key components. Firstly, you have your backbone, which is essentially the highway that the data travels. On both ends of the backbone are terminators, which are resistors that absorb the signal energy ensuring that it is not reflected back onto the network (It is extremely important to only use these terminators on the ends of the backbone and not as covers on spare tees). Next, you have your tees which are intersection points allowing the equipment to be connected to the backbone via a drop cable. Finally, you have your power tee which provides energy to the network.
When setting up a network, there are some further restrictions that must be taken into account. Some of these restrictions are as follow:
Maximum Backbone Length: 100m
Maximum Drop Cable Length: 6m
Maximum Total Drop Cable Length (entire network): 76m
Voltage Input: 9-16 VDC
Power Requirements
On most N2K systems, the power requirements are relatively moderate and straight forward. But as a network increase in LEN or backbone length, it is important to verify network voltage drop.
To calculate voltage drop, you can use the following formula:
Voltage Drop = LEN x Backbone Length x 0.006
If the voltage drop exceeds 1.5V, data errors can occur which will cause significant issues on your network. If you exceed the 1.5V limit, the installation of a power insertion point may be required. Alternatively, if the backbone length can be reduced through the removal of coiled cables, or the power tee can be relocated to a more central location on the network, voltage drop issues could disappear.
SeaTalk NG/SimNet
SeaTalk NG (Raymarine) & SimNet (NAVICO) are manufacturer specific solutions to NMEA2000 protocol. These systems use the same communication protocol as NMEA2000, and with the appropriate adapters can be integrated into a N2K system.
With any new network installation, we recommend avoiding the use of these systems due to the availability of standard N2k equipment and the market trend that manufacturers are following in providing equipment with standard NMEA2000 connections.
Troubleshooting
If you are experiencing issues with your NMEA 2000 network, there are several steps you can take to troubleshoot and resolve the problem:
Check the physical connections: Make sure all devices on the network are securely plugged in and that the connections are not loose or damaged.
Check the power supply: Ensure that the power supply is functioning properly and that all devices are receiving power.
Check the network configuration: Make sure that all devices on the network are properly configured and that the network is set up correctly. This may include verifying the baud rate, device addresses, and other settings.
Check for software updates: If you are using devices with software, make sure you have the latest version installed. Outdated software can sometimes cause issues on the network.
Check for physical interference: Make sure there are no physical obstructions or sources of interference that may be affecting the network. This may include other electronic devices, electric motors, or alternators.
Check for diagnostic messages: Some devices may provide diagnostic messages that can help identify the cause of the issue. Check the manufacturer's documentation or consult with the manufacturer's technical support for more information.
Check to ensure the network is properly installed. Verify the correct ports on the NMEA Tee are being used for the backbone and drop cables.
Ohm out terminators on either end of the network. There should be a resistance of 60 ohms.
If you are unable to resolve the issue using these steps, you may need to consult with a professional such as Sea & Land Yacht Works for further troubleshooting.