Category Archives: Marine Data Networks

Marine Data Networks

8/7/2017: Updated “Hardware” section to include Rose Point LLC’s announcement, dated today, of “nemo™” “Signal K” device.

There was recently a question on a forum I follow asking, “are there devices that can allow different network technologies to ‘talk to one another.'”

Just understanding that question requires some knowledge of computer and network technology.  The question is asking if there is the capability to share data created by a software application on one computer with one or more software applications running on another computer.  That capability is actually extremely complex to achieve.

Networks are the “roads” over which digital data travels between computers.  The Internet is just a large and complex “highway system” for digital data travel.  Just as “roads” range in size from dirt trails to interstate highways, computer “networks” range from slow, limited in capacity to very fast and enormous capacity.  Just as Interstate highways can carry more traffic than city streets, some network designs carry more data than others.  Cars and trucks travel on highways.  “Units” of data travel on networks.  Each unit of data on a network is like one car on a highway, in that it can have a different destination than the unit in front of it or the unit that follows it.  Just as there are many sizes/shapes/brands of cars and trucks, there are many different formats for individual units of digital data.  Trains travel on a specific road bed called “tracks,” while cars travel on a specific roadbed called “pavement.”  Networks are designed to handle one – and only one – particular format-type (Syntax) of digital data, so a different unique network is required for each different format-type of data.

Increasingly, the navigation equipment found on pleasure craft are actually computers running operating systems (usually Linux) and software applications (called “firmware”).  Chart Plotters, AIS receiver/transponders, VHF Radios and autopilots are all special purpose computers.  These devices are connected together with network connections consisting of pairs of primary wire, coaxial cable, multiplex cable varieties, or radio waves in the case of Bluetooth and Wi-Fi.  They have imbedded operating systems and run apps of functionally-specific “firmware” which exchanges various kinds of information (depth, heading, course, speed, cross-track error, position, temperature and many more), back and forth among the components of the navigation suite.

So the question, “are there devices that can allow different network technologies to ‘talk to one another,'” is very complicated.  The real answer is neither “yes” nor “no;” the real answer is: “maybe;” “sort of;” “sometimes;” and “it depends.”

Over the past 15 years, the navigation electronics designed for and deployed on pleasure craft has exploded in function and complexity.  There are several excellent and highly competitive marine electronics manufacturers, each with worldwide markets, producing navigation equipment components and systems.  There are also companies specializing in developing sophisticated vessel monitoring and accessory equipment.  That explosion of marine function and technology has been accompanied by a similar explosion by technology companies that manufacture portable, durable, highly functional general-purpose consumer electronics and computing products.  There are many general-purpose computing equipment choices today that boaters did not have as recently as 5 years ago.  It’s highly likely the current rate of development will only accelerate in the near term future.

Whether in the realm of specialty navigation equipment or general-purpose equipment used to support navigation tasks, there are several technical realities that underlie the complexity of the navigation electronics market.  Key technology areas include:

  1.  data formats and data-exchange networks,
  2. capability of hardware devices, including designs for backward compatibility, and
  3. availability and capability of software applications, whether in the form of device-specific  firmware, smart phone apps or PC operating systems with application software, that all need to interoperate.

As youngsters learn to play various sports, they must learn the terms that go with the game.  In baseball, for example, the young ‘un must know what a “ball” is; a “bat;” a “base;” a “diamond;” a “hit;” a “strike;” a “foul;” an “infield fly;” an “umpire.”  In a discussion of digital data and networks, there are terminology and concept basics that need to be understood.   For this article, following are some of “the basics:”

  1. Interoperability – The ability of a buyer to purchase equipment from different manufacturers and be able to install that equipment into an existing suite of equipment with confidence that it will all work together.  When many different manufacturers make products that overlap in capability and are intended to provide the same functional capabilities in the same target market, “interoperability” is an essential requirement of the buyer/end user.  “Interoperability” must be designed into the equipment.  These designs are implemented by adherence to various industry standards and the architectural protocols of the communications network that the equipment utilizes.
  2. Syntax – The specific sequences of control information and user data that make up units of data traveling in a particular network.  In NMEA0183, data units are called “sentences;” in NMEA2000, data units are called “Parameter Group Numbers;” in Ethernet, data units are called “packets.”  The specific format of these units of data are all different from each other, but the construction of each kind of data unit follows very specific architectural rules.
  3. Protocol – Any defined, standardized scheme used to pass data between devices by which the data sent from one device can be received and correctly interpreted by another device.
  4. Simplex – A one-way (uni-directional) communications link between a device that sends data (like a compass sending a heading) and another device that receives data (like a chart plotter displaying a compass heading).  This technology can use a single pair of signal wires.
  5. Duplex – A two-way (bi-directional) communications link, like a telephone conversation.  In digital communications, this technology typically uses three wires, Transmit Data (TD), Receive Data (RD), and signal ground
  6. Serial – Data that is transmitted bit-by-bit, like typewritten words.  Think of a keyboard (typewriter), where the words of this article were created serially, letter-by-letter.
  7. Parallel – Data that is handled in frames of predetermined length.  The two most familiar items here are “32-bit” and “64-bit” operating systems.  What that means is that the internal processor chips and “motherboard” can handle either 32-bits or 64-bits at a time, instead of just one single bit.  Parallel operations add cost but speed up computer and network throughput speeds.
  8. NMEA0183 – A “first generation” marine serial data communications protocol standard of the National Marine Electronics Association (NMEA), used to enable interoperability between other NMEA0183 made-for-purpose navigation devices, including devices made by different manufacturers.  Furuno, Garmin, Raymarine, Sitex, etc, etc. all make GPS receivers, depth sounders, chart plotters, autopilots and weather instruments that can share their data (Interoperability) on a client’s boat because they all follow the same data architecture standard.  This network uses a pair of signal wires (data signal + and electronics ground).
  9. NMEA2000 (N2K) – A “second-generation” marine serial data communications protocol standard used to enable interoperability between N2K devices made by multiple manufacturers.  Faster and more extensive than its NMEA0183 predecessor standard, N2K includes support for data from accessory equipment (engine operating and performance data, battery monitoring data, bilge pump and tank level monitoring data, and more).  This network uses a 5-conductor cable with standardized connectors.
  10. CanBUS – “Controller-Area Network Bus,” is the technology used by the “computerized controllers” found in modern cars and trucks, worldwide.  N2K as used in marine applications is a CanBUS-compatible spin-off of the parent CanBUS technology platform.
  11. Ethernet – The full-duplex networking protocol standards (wired and wi-fi) used by general-purpose computers to exchange data over the public Internet.  The wired form of this technology uses Category 5 or Category 6, 8-conductor cable with RJ-45 terminal ends.  The wireless form of this technology uses two segments of the radio frequency spectrum.
  12. Multiplexor – A simplex (one-way) device that can monitor and forward data passing through NMEA0183 and/or N2K networks, at a minimum.  Some can also include Raymarine Sea Talk network data and Furuno NavNet data.  Multiplexors are designed to bridge data to another network and convert the data format so that it can be used in another kind of network (ex: NMEA0183 to Ethernet).  Conversion of data from one network syntax to another is a function requiring firmware intelligence.
  13. Signal K – An emerging full-duplex (two-way) technology that can convert data between NMEA formats and general-purpose Ethernet formats used by general-purpose computer networks.  This extended function allows the otherwise non-compatible NMEA networks to interoperate with laptop computers, tablets and smart phones using Ethernet (wired or wi-fi) communications networks.

Anyone who has ever read an advertising or marketing brochure for a marine navigation product has been faced with an array of technology terminology (“techno-babble”) like the above.  The “techno-babble” is often confusing, even confounding.  “It sounds wonderful, if I only knew what they were talking about!”  Adding to the confusion, each manufacturer has its own terminology for its features and capabilities.  Furuno has “NavNet.”  Raymarine has “SeaTalk.”  They are the same things by different names.  The manufacturer-specific marketing “techno-babble” adds to the complexity of comparing the capabilities of equipment from different manufacturers.

Data Networks and Data Exchange:

Interoperability is not necessarily a goal of marine navigation equipment manufacturers.   Garmin International has a corporate policy to keep much of their data proprietary.   For other manufacturers, that makes designing for interoperability with Garmin equipment difficult or impossible.  For example, Garmin does not share their autopilot control data syntax with Rosepoint LLC, the developer of Coastal Explorer navigation software.  Thus, Coastal Explorer cannot load route data into Garmin chart plotters.  Garmin’s goal is to “incentivize” buyers of their equipment to stay brand-loyal, since only other Garmin equipment can fully utilize Garmin proprietary data and capabilities.   Conclusion: Garmin doesn’t want true interoperability with other equipment manufacturers.

NMEA0183 (simplex) and NMEA2000 (“N2K”) (full-duplex) are communications network standards for two types of serial networking technologies.   Figure 1 shows the NMEA0183 network model:


Figure 1: NMEA0183 Simplex Network Model

Figure 2 shows the NMEA2000/CanBUS network model:


Figure 2: NMEA0183/CanBUS Full-Duplex Network Model

In an NMEA0183 network, the data units that travel the network are called “sentences.”   In an N2K network, the date units that travel the network are called “Parameter Group Numbers,” or “PGNs.”  The names aren’t important to the average boater.   What is important to know is that these two types of digital data packaging are not compatible with one another.

Within the two NMEA data standards, there are specific sections that provide for manufacturers to use proprietary data syntax.   Several manufacturers, including Garmin, Simrad, Raymarine, Stowe, the Brunswick Corporation, Mastervolt and others, use proprietary data for at least some of their device functions.   If a manufacturer chooses to use proprietary data for any given function, that function may or may not operate correctly in a network involving equipment made by another manufacturer.   More likely, most of the design features will work, but one particular feature – or feature subset – may not.   If that feature isn’t important to the buyer, nothing is lost.   If that feature is important to a buyer, well then, there will be disappointment.   It is not always possible to know in advance if that will happen in any given mix of equipment from multiple manufacturers, so the reality is, there is no absolute guarantee of interoperability.  Adding to the complexity of the technologies is the fact that equipment features and functions change every year as new gear rolls out.  It’s often good advice to stay with a brand if that brand meets your needs.

N2K is an “evolutionary descendant” of another communications protocol called CANBUS (Controller Area Network).   CANBUS is the networking technology used worldwide in automobiles and trucks.   CANBUS is a very fast and very reliable full-duplex serial network.  On boats, it allows modern diesel engine performance monitoring data to be included in an N2K network.  So for example, a marine chart plotter may have the capability to display Cummins or Caterpillar or Volvo engine operating and  performance data.

With the N2K and CANBUS standards, there is no native provision for an interface to an Ethernet network as found on a general-purpose consumer client devices (Server platforms, PCs, tablets, smart phones).   The World-Wide networking standard for general-purpose clients is IEEE 802.11 a,b,g,n wired Ethernet or IEEE 802.3 Wireless Fidelity (wi-fi) Ethernet.   Some marine manufacturers are in the process of adding Ethernet capability to their equipment, as a option for proprietary features/functions if not as a backbone communications network.   Anyone with a requirement to use a general-purpose client device within the Navigation suite will need a way to interface to the NMEA incompatible networks: NMEA0183 and N2K to Ethernet.  Check carefully on any device you purchase that has Ethernet built-in.  It may not be there to support interoperability with general-purpose client computers.


NMEA0183 is a simplex and serial network technology.   The incoming port to a device is known as the “Listener.”  The outgoing port from a device is known as the “Talker.”   Talkers cannot listen, and listeners cannot talk.   By design, an NMEA0183 network is limited to one, single “talker,” and about 4 – 6 listeners.   On most boats, even a “basic” navigation suite of compass, GPS, chart plotter, depth sounder and DSC VHF Radio will need several NMEA0183 networks to function as an integrated system for the user.  Both as new installations and for equipment upgrades, these networks can be a challenge to lay out, can be hard to expand in stages, and will require careful planning and forethought.   Figures 3 is a view of the five NMEA0183 networks I have installed in Sanctuary:



Figure 3: Sanctuary NMEA0183 Networks

Most marine instrument hardware today is made with both N2K and NMEA0183 built-in the unit.   The NMEA0183 interface supports backwards compatibility with older devices that have only an NMEA0183 interface(s).  Today, manufacturers add both NMEA0183 and N2K interfaces to most products in order to support an upgrade path from the old technology to the new.  This allows buyers to add devices with the faster, newer, more functional N2K networking technology in small and affordable increments.  Many – but not all – marine hardware devices support two NMEA0183 listener ports and two NMEA0183 talker ports in addition to an N2K port.   These devices can listen to incoming data on one incoming NMEA0183 listener port and spit it back out again (forward it) on an outgoing talker port.  In that way, data can be bridged to a second NMEA0183 network.   Specific data that can be forwarded is a function of the individual device.  Not all devices can forward all data.

Today, there are devices called “multiplexors” that can translate network data formats into formats needed by other network technologies.   Multiplexors can “listen to” NMEA0183, N2K, Furuno NavNet and Raymarine Seatalk networks and translate that variety of data into Ethernet formats that can be used by a computer or tablet.  Multiplexors can also translate NMEA0183 sentence data into PGN format and forward that data to an N2K network.   Most multiplexor solutions today are simplex (one-way), from the navigation suite to the PC/tablet.   Figure 4 shows the fully integrated suite of equipment aboard Sanctuary, including NMEA0183, N2K, the multiplexor and Wi-Fi.


Figure 4:  Integrated Suite of Equipment, Including NMEA0183, N2K, a Multiplexor and a Wi-Fi Feed For Use By PC and Tablet.

Today in 2017, there is a new development initiative underway.  It is an evolutionary descendent of existing communications network technology, not a new communications protocol standard.   Called “Signal K,” this is being lead not by a manufacturer, or a group of manufacturer’s, but rather a private group (open-source) of software developers.   Signal K is intended to be a full-duplex (bi-directional) solution.  That is, the Signal K hardware (gateway) will assemble NMEA0183 and N2K data and forward it via Ethernet protocols to a PC or tablet, and will receive Ethernet packets from from a PC or tablet and translate that data into NMEA0183 or N2K formats.   The idea is to create an full-duplex network technology platform that truly provides full interoperability.  The developers of Signal K claim that this solution will support Nobeltec, Rosepoint, iNavX, OpenCPN, MacENC, Polar Navy, iSailor, Navionics and other software applications runing on general purpose computing platforms (Servers, PCs, Tablets), all wirelessly via wi-fi feeds.

One such physical gateway is called iKommunicate.  The iKommunicate solution is, in 2017, an emerging technology.  Flash: today – 8/7/2017 – Rose Point Software announced their new “Signal K” gateway, called “nemo.”  Information on “nemo” is available here:  These devices are really highly specialized computers.  They are analogous to the Small-Office Home-Office (SOHO) Ethernet routers that are familiar to most of us.  They don’t do a lot, but what they do, they do very fast and very well.  In the case of iKommunicate, they are data translators, translating between the syntax of data arriving and leaving via different network protocols.

With a multiplexor solution, a computer or tablet application can listen to GPS position data and compare it to a pre-planned route installed on the computer.  A multiplexor is a simplex device, and cannot talk back to the network, so cannot provide control information to correct the course via the boat’s autopilot.   With the Signal K solution, application software running on the Laptop or tablet would be able to control and correct an off-course condition via the full-duplex Signal K network bridge.


In order to monitor, control and correct for dynamic situations and asynchronous events that occur on the water, a PC or tablet software application solution that has the needed intelligence and decision-making capabilities is also required.  The network alone is not enough.  Today, there are very few software applications that can do that, and NONE that I know of that can do it for all navigation functions.   The two most popular tablet apps – Garmin Blue Chart Mobile and Navionics – can’t do any of this.   MacENC on Mac OSX can do some functions for Mac users.   Coastal Explorer on Windows can perform some functions.   SEAiq is available for iOS and Android Tablets as well as Mac OSX and Windows PCs.  SEAiq can do some driving.   Consider though, if Garmin will not release the syntax of proprietary data to Rosepoint or SEAiq developers, then the apps cannot fully support these manufacturers devices.


So, yes, Virginia, there are devices that can allow different network technologies to “talk to one another.”   But, there’s more to it than just talking.   Just having the network is not enough.  Consider this scenario: put three people in a room, one a speaker of only Mandarin Chinese (syntax), one a speaker of only Arabic (syntax), and one a speaker of only English (syntax); yes, they will be able to talk at one another, but they will not understand one another.   Intelligence is needed to provide translation and understanding.  That is very much what exists in the navigation networking and data realm in 2017.  Any data converter or software application solution will need to understand and translate all three languages (data syntax) in all application areas.

Today, as in the early days of computers, end users of nav equipment must understand more of the technology than they would like to have to understand.  In 1995 or so, my neighbor ran a home-based medical transcription business.  Just to type dictations and send the finished transcriptions to the hospital medical records department, she needed to know a great deal about Windows and network connectivity, for which she had neither background, training nor inclination.  That’s how it is today for navigation electronics on pleasure craft.

Watch this space, though.  In a relatively little time – even today at the high end – we will have equipment that fits into systems, introduces itself as plug ‘n play, and just works.  We will have software apps that allow us to take advantage of all of the features the manufacturers design into their equipment.  And, we will be using PCs instead of made-for-purpose equipment, because it is both less expensive and more functional and flexible.  Were it not for the lack of full-feature software, I would be using only my iPad for navigation today.  As that gap closes, it may well become an all tablet world.