BMEA

Nick Heyes is Managing Director of Marine Electronic Services Ltd (www.mesltd.co.uk), the UK’s leading specialist marine electronics reseller.   They sell a wide range of electronics and are well positioned to see the trends that are happening with interfacing.  Here are his thoughts on NMEA2000 developments….

Back in 1983, the National Marine Electronics Association in the US developed the NMEA 0183 data standard.  It was designed as a method to get onboard electronics to intercommunicate – typically a LORAN or Decca connected to a plotter or a plotter connected to an autopilot for automatic waypoint to waypoint steering.  The communication standard was based around a single device transmitting data (a talker) with connections to one (or many) receivers which acted as listeners.  Data speeds were limited to 4800 baud which equates to a maximum transmission speed of approximately 12 messages every second. 

High speed NMEA 0183 at 38400 baud was developed later for systems requiring more data throughput such as AIS, but even so, with today’s complex systems combining compass, GPS, instrumentation, AIS and more data, the NMEA 0183 data standard quickly ran out of horse power.  There was also no standardisation of wire colour coding, no certification process, no common cable or connectors and as such there were a lot of ambiguities within the NMEA 0183 standard which led to inter-operatability problems between different manufacturers.

Clearly there was a requirement for a new higher specification standard and back in 1994, NMEA 2000 development began.  The NMEA 2000 data standard was developed around CAN bus technology which is commonly used in automotive control and engine monitoring applications.  There are, of course, other data standards such as ethernet which offer significantly higher bandwidth capability but the CAN data standard was chosen as it consumes less power, is more cost effective for simple sensors such as temperature, voltage, speed, depth, wind etc and it can also be prioritised for real time control applications.  Because CAN is time determinate and hierarchical,  it means critical messages such as steering, throttle or other safety critical data can be effectively prioritised within the system. 

On a physical level, NMEA 2000 was designed to have adequate bandwidth to accommodate future needs, to be cost effective to implement and to offer failsafe and redundant capability – with a simple plug and play connection with defined connectors and cabling based around a backbone and spur system.

NMEA 2000 specifies cables and connectors to ensure plug and play capability and is based around a standardised, waterproof, thin cable with 2 wires for data, 2 wires for power and ground and a common shield wrapper.  The data pair and power pair are independently shielded to minimise interference and the whole backbone system is engineered for serviceability allowing devices to be plugged or unplugged without powering down the network and that also ensures that if a device fails, it does not affect the remaining network.

Field installable standard connectors make installations and fault finding much easier

A basic NMEA 2000 network consists of a backbone cable with individual items connected through spurred T pieces – like a spur running out of the network.  Power can be applied centrally through a suitable power tap and at each end of the backbone, a terminator is fitted to complete the installation.

 Typical small NMEA 2000 system showing backbone and cabling

The benefits to the user and boat owner are enormous in that one single cable can provide power and data for every product and any manufacturer’s equipment can be connected to the system so long as it is NMEA 2000 certified – that means no ambiguity, with products truly working “out of the box” and equipment can be added with ease at anytime in the future based on the open data standards of NMEA 2000. 

However, as with any data standard, it does rely on the “industry” as a whole to take up the standard and over the past 16 years, introduction of the NMEA 2000 data standard has been slow – in fact painfully slow!

Initially, it was hoped that boat builders would pre-wire boats for NMEA 2000 – or at least provide a backbone so that the boat was future proof.  In practice, this hasn’t happened and that’s primarily due to the cost of initially providing the cabling system but also due to the dominance of a handful of manufacturers who have promoted their own data networks and proprietary systems. 

The good news is that in the past two years, development and installation of the NMEA 2000 systems has become exponential with a sudden drive for more inter-compatibility in interfacing standards.  Many of the leading manufacturers have adopted it but some have taken a rather blinkered approach (and potentially quite foolish) by calling their N2K data system with a proprietary name – For instance, Simnet from Simrad or SeaTalk 2 from Raymarine.  These data standards, whilst based on NMEA 2000, can contain some proprietary information which makes true plug and play interfacing still problematic and subject to issues.  Frustratingly, some systems are even continuing to utilise older NMEA 0183 data standards to interconnect as this is providing an easier method of interconnection.

So where do we go for the future?  There’s no doubt that the NMEA 2000 data standard is here and is progressing sufficiently fast now to entrench itself into every marine electronics installation.  Most importantly, it is important for a buyer of modern marine electronic products to call on the expertise of a professional, knowledgeable supplier who’s previously configured systems like this.  It is frustrating that it is still not a plug and play data standard with every system requiring a bespoke amount of tinkering and tweaking in terms of interfacing to get the best possible solution – but that’s where a knowledgeable supplier can help .  There are still inter-compatibility issues between products and the protectionist approach by many of the larger manufacturers means that mixing equipment across brands can still cause huge interfacing headaches. 

NMEA 2000 also has competition with the ethernet method of inter-connecting with many manufacturers utilising ethernet on a proprietary basis.  Leading manufacturers’ like Garmin, Raymarine, Furuno and Lowrance all use a 100MB network type connection to share sonar, radar and charting information across a range of multi-function displays.  These are all proprietary networks with no common standard so whilst the cabling and terminations may be identical, the format of data is different from every manufacturer.  You can’t mix and match displays or sensors across manufacturers.  This heavy weight data standard does not lend itself to smaller systems such as depth, speed, wind etc where the inclusion of a costly ethernet interface would add substantially to the price of an instrument.  So there is a place for both standards to co-exist and operate within the marine environment and certainly if I was choosing a marine electronic item today, I would like to see an N2K compliant sticker on the outside of the box!

For further information, please contact:

Marine Electronic Services Ltd, Marine House, Unit 10, City Business Park, Easton Road, Bristol BS5 0SP.
Telephone: 0870 122 1099.  Fax: 0870 122 1098.

Email: sales@mesltd.co.uk

www.mesltd.co.uk