I’ve been looking forward to typing up this blogpost for a while, but I haven’t quite managed to get to it since the project it concerns have taken a while to get fully completed.

Boat electronics happens to be an interesting topic to me. With a background and education in IT and Software Engineering and having fiddled with electronics for most of my life, this is an area of much curiosity and joy.

Overview of current equipment

Our boat was refitted somewhere around 2004-2005 with a complete Raymarine system, top-of-the-line at that time, hooked up to a Seatalk network bus to which the following equipment were connected:

  • Raymarine windvane 
  • Airmar depth sounder
  • Airmar log and temperature sensor
  • Raymarine ST5001 Autopilot Controller with Fluxgate Compass, rudder angle sensor and a linear drive actuator, connected to the steering quadrant.
  • Raymarine ST7001 Doubled autopilot controller
  • Raymarine ST60 Tridata
  • Raymarine ST60 Wind instrument
  • Raymarine GPS Antenna
Raymarine ST60 TriData Display

Plotters

We have dual Raymarine RL70C+ Chart Plotters (one in the cockpit and one at the nav station). These are linked using Raymarine proprietary network called HSB (High Speed Bus) which means they can share chart data, settings, routes and radar data. The plotters hold dual slots for charts memory cards and when you hook them up via HSB you can have them both access chart data from four memory cards at the same time.

These plotters are built like tanks and although the software is slow, by modern means of measure, they still function perfectly. They have excellent brightness and heavy duty buttons (touchscreens were still only a dream in those days). Replacing them would mean throwing tonnes of money into the boat and replacing a wide set of electronic charts.

Raymarine RL70C+ Chart Plotter

This is a very clean setup and the only addition we’ve done to it previously is to add an additional plotter to the Nav Station. For all intents and purposes, this setup has served us very well and with the significant investment made by the previous owners it feels silly to throw this out and start again.

New requirements and new gear

The reason we have started fiddling with this setup at all is that we have the need to add additional equipment for safety and navigation purposes. We have decided to add a radar for low visibility and nighttime navigation as well as an AIS Transponder, for similar reasons. 

  • Raymarine RD218 Radar – We bought this one almost three years ago and it has been sitting in storage since.
  • ICOM423G VHF Featuring a built in GPS
  • Camino 108S Class B AIS Transponder – Just released in 2017

In addition to adding this equipment, we have realised we want to be able to use navigational data on an iPad, phone or laptop connected to the boat WiFi.

Raymarine RD218 Radar

The radar hooks up easily to the Raymarine plotters. They will share the radar data between themselves over the HSB connection. The plan is to connect it to the plotter at the nav station as running the cable to this position is far easier than wiring it to the steering piedestal.

ICOM 423G Fixed mount VHF

We previously had a Raymarine VHF which had failed some years ago. It could only occasionally receive a clear signal and transmission was broken entirely. Not very trustworthy so we decided to replace it with a tried- and trusted unit. The ICOM423G VHF has the essential feature set you expect of a modern VHF. As a bonus it has a built-in GPS receiver, which is a good backup to have, should any of the other ones on-board fail. The GPS data received can be used by other instruments if you hook it up to your NMEA0183-bus (more on that further down).

Camino 108S AIS Transponder

The AIS Transponder, for those of you who are new to this type of equipment, is a device which connects to the VHF antenna and continuously broadcasts the boats current position, speed, heading, name and Callsign. It uses a dedicated GPS-antenna to acquire this data. It also receives this data from other vessels within transmission distance.

Transmitting data is the key security feature from our point of view. Being a small vessel, it feels comforting to know that larger vessels can spot you on their displays and collision alarms. It also means that people ashore, can see where we are at any given time, should anything occur.

The data we receive from the AIS Transponder can be used to display, on a chart, other vessels, their direction, speed and heading. Using a collision alarm we can get warnings should we be at risk of colliding with another vessel, based on a calculation using the two vessels speed, heading, and location data. 

The AIS Transponder connects via a network called NMEA0183 to other marine equipment and via USB to a computer. Just using the transmitting feature does not require any additional fiddling with networks. But if we want to use the received data, then we need to work out a solution.

This means we have to tackle the task of interfacing a wide range of equipment, from different manufacturers. I’ll try and explain how you could go about doing this. First, let’s talk about boat networks!

What is Seatalk?

Seatalk is a proprietary instrument network owned by Raymarine. It was superseded by Seatalk NG as NMEA2000 entered the scene. The Seatalk network cabling is very simple, it consists of three wires: power, ground and one signal wire. This means all equipment connected to Seatalk can be powered directly off the bus itself. 

In order to use the data on the network by any other type of equipment, a converter needs to be added to the network. These come in various forms and can translate back and forth between Seatalk and other protocols.

NMEA0183

NMEA0183 is a network specification (electrical and data) which has been widely adopted by marine electronics manufacturers. If you have a boat of about ten years of age it very likely has a NMEA0183 backbone. This spec has been replaced by NMEA2000 which is the dominant system implemented on modern boats.

NMEA0183 wiring is also simple, although it does not carry power on the bus. Rather it has a positive and a negative signal carrier. I won’t go into details but the key thing to understand is that you cannot simply wire together an NMEA0183 and a SeaTalk network without some additional equipment.

Converting and combining data streams

There are a number of options for converting and combining data from two or more networks. Some chart plotters and Autopilot controllers has a built in SeaTalk-NMEA bridge. That is the case with both our RL70C chart plotters and our ST5001 and ST7001 AP controllers. 

When combining equipment of different ages and purposes you might also run the risk of introducing problems caused by different transmission speeds. SeaTalk has a transmission speed (called Baud rate) of 4,800bps. This means 4,800 symbols (or characters) per second can be sent over the network. The AIS Transponder has a transmission rate of 38,400 bits per second. Simply wiring this up to one of our plotters for bridging would wreak havoc on the SeaTalk Network.

The solution when you are in this situation is to introduce a piece of equipment called a Multiplexer. 

The Shipmodul Multiplexer

Shipmodul is a Dutch company who makes marine multiplexers of various sorts. I bought the MiniPlex-3USB-N2K last year and it has functioned excellently, thus far allowing us to hook up a laptop, via USB, to read data off of the SeaTalk network. It also has allowed us to hook up an additional Raymarine Plotter and get wind, heading, speed and other data to display on it.

The beauty of a Multiplexer like this is that you hook up all your buses to it: SeaTalk, NMEA0183, and NMEA2000, and then you configure in software how these buses should interface to each other. You can define, down to individual message types, what data should be transferred from and to each bus. The Multiplexer handles the problem of connecting equipment of different data speeds to one another with (relative) ease.

The Multiplexer has a USB-interface which you connect to a computer. Then you use a special software from Shipmodul to carry out and troubleshoot the configuration. After some reading this is fairly straightforward.

Shimodul MiniPlex-3USB-N2K Multiplexer

Getting data onto your wifi

I said in the beginning that we wanted to be able to use data from the instrument networks on a tablet or an iPhone via WiFi. To solve this problem, you could purchase a router from Digital Yacht, which will create an onboard wifi and allow you to hook up NMEA0183 to it. This equipment however, is quite costly. Further, we already have a 4G Broadband Router which we use for laptops and for streaming data. 

The slightly more complex solution required, to get instrument data onto the network created by the 4G router, involves a Raspberry Pi microcomputer.

Raspberry Pi 3 Model B+

Raspberry Pi

The Raspberry Pi microcomputer is an incredibly versatile (and affordable) piece of equipment. It is in essence, a PC which can run a range of Linux operating systems. It has four USB ports, an HDMI-port for video, built-in wifi and bluetooth and a GPIO allowing you to connect all sorts of electronics such as temperature sensors, lights, displays and whatever you want to play with.

Our use of the Raspberry Pi is fairly simple. It’s one and only role is to be a client on our WiFi (created by the 4G router) and to broadcast the NMEA data stream onto that network.

The Raspberry Pi runs the Raspbian Linux distribution. We use a VNC client to connect to the desktop on the unit and to be able to start and stop applications. The unit is connected via USB to the Miniplex, which sends all NMEA data to the Raspberry Pi.

To get the data on to the WiFi-network, we run a simple program, called kplex, which reads data from the serial port (the USB-connection) and broadcasts it via UDP over the wifi. The data stream can then be read from any computer, laptop or smartphone which is connected to the same network.

The newly refitted nav station as of 2018

Lessons learned

This all seems straightforward and simple. Of course, in retrospective it seems just like that. However, there has been a number of obstacles to overcome along the way. Everything from troubleshooting wiring connections, configuring the multiplexer and setting up the Raspberry Pi and kplex software.

If you plan on expanding your current setup I strongly advise you study what gear you already have, what connections it has and also to get straight what requirements you have when adding new gear. By thinking ahead you understand what, for instance, type of multiplexer you will need.