Marine Electronics

Introduction to Data Networks

In order to fully understand marine electronics it's important to consider exactly how on board electronic devices 'talk' to each other, and a good way to introduce the important elements of this process is to consider how we as people communicate with each other.

For example:

You want to communicate with a friend so you call on the phone - there's a telephone system to carry the signal, you're both using the western alphabet, with English language used to form the words and sentences conveyed as audio, you're both speaking and listening at a mutually acceptable rate, taking turns listening when the other person is talking, and you both know what to do or say if you don't understand, or can't hear the other person; for example if it's noisy where you are and your friend can't hear your voice over the background noise.

With Data Networks, all these protocols, nuances, and etiquettes have to be clearly locked in place by a common standard if electronic devices are to be fully compatible, and during this first section of Boat & Yacht Electronics you will learn about all the various standards in place - in great detail!

With Marine data communications, If any one single one of the elements above are missing - devices will not be able to communicate. As an example - this could mean that the vessels crew have no means to access the vessels position data simply because the device producing position data can not talk to the device that displays it.

Introduction to Data Networks Video Lesson

The video presentation below serves to introduce typical Marine Data Networks that you find on many vessels from as far back as 1983, right the way up to present day, but also the future standards in development.

Low Speed Data system

To get the ball rolling, let's just quickly look at a few basic, most common electronic devices you might find on board, that communicate with a low speed data system:

1. GNSS Global Navigation Satellite System (GPS)
2. VHF (Short range radio communications)
3. Multifunction display(s) (chart plotters with radar and other functions)
4. Depth Sounder
5. Wind indicator
6. Log
7. Electronic compass (fluxgate)
8. Autopilot

In order for electronic devices to communicate with each other they all must adhere to a recognised standard, just like your computer will work with a mouse that is USB for example, the USB communications standards have to be set so that any manufacturers' USB mouse will work on any computer with USB functionality.

Data Standards

In the maritime world the main body defining the standards of how devices 'talk' to each other is the NMEA National Maritime Electronics Association. These NMEA standards have also been recognised as the international standards by the IEC International Electrotechnical Commission.

In conjunction with this, a company by the name of Autohelm / Raytheom now known as Raymarine have along the way created their own proprietary standard 'SeaTalk' so we are going to look at these guys too.

Maritime Electronic Communication standards since 1980

• NMEA 0183 / 0183HS 1983 - 2002 still in use
• Seatalk 1 1989 - 2002 still widely in use
• NMEA 2000 2000 - present day
• SeaTalk NG / Sim NET / Furuno Can (NMEA 2000) 2002 - present day

There is much more to come on how we work with all these systems, and pretty much anything can talk to anything with the right converters, but it's important at this stage to fully understand the various standards.

High Speed data

Forget Kbps, now we're in Mbps territory!

The higher speed data network is required for equipment such:

• CCTV,
• Night vision
• Radar
• Networking multiple MFD's

High speed data networks are based around the existing Ethernet system using internet protocols, and whilst we call them high speed in this context, this is only to differentiate from the the much lower speed NMEA networks.

High speed data communications between typical boat and yacht electronics is usually around 10 to 100 Mbps; to put this into context most office LAN networks can run at more than 1000X faster

Why so slow? We don't actually need such high speed data for the task in hand, just as your computer keyboard doesn't require a high speed data connection to your computer (unless you can type at 10000 words a second)

Many yachts also have third separate high speed data internet based network with Wifi end everything else, for watching Netflix etc, this network is considered separate from the navigation networks. What we need for navigation is reliability, rather than lightning speed, most of what our instruments have to say is rather brief.

Even the old NMEA 0183 standard is still very much in use today in commercial shipping, why? Because it works well when used as it was designed, the low data rate is not an issue. A single 4800 bps connection was only really initially designed for one talker and one listener, if you consider a depth gauge for example, it will send the depth value around twice per second.

In the next few sections we will cover the various data standards in great detail.