Keeping up to date with the latest navigation technology can be prohibitive. Mike Reynolds shares how to get the latest electronics for your boat for a fraction of the cost

Electronics technology is constantly improving, offering ever more impressive capabilities, writes Mike Reynolds.

It is making navigation easier, quicker and more accurate, and useful information easier to access.

It’s making recording and displaying historical data possible, supplementing the real-time (now) data we’re used to.

It costs, but only if substantial replacement of hardware is necessary.

We decided we wanted the best of both worlds — standard hardware with longevity, and software with the flexibility to take advantage of emerging trends.

OpenCPN offers clear, easy-to-use chartplotting and navigation functions.

OpenCPN offers clear, easy-to-use chartplotting and navigation functions. Credit: Mike Reynolds

We are electronics enthusiasts and configuring electronics isn’t everyone’s cup of tea.

But a little effort can deliver the very latest capabilities, tailored to your boat, for minimal additional cost.

For those not inclined to experiment, this article illustrates capabilities coming to future ‘plug and play’ systems.

Our boat Zen Again is a 1980s 34ft 3/4 tonner which we purchased 10 years ago.

She is fitted with a robust cruising navigation and communications system, with built-in redundancy.

For some years we’ve used standard NMEA-2000 sensors for position, speeds, depth and AIS.

The data is sent via WiFi to a laptop at the chart table and waterproof tablets on deck.

Zen Again is a ST10.4, a 1980s IOR three-quarter tonner designed and built in Japan.

Zen Again is a ST10.4, a 1980s IOR three-quarter tonner designed and built in Japan. Credit: Mike Reynolds

Recently we’ve added a NMEA-2000 weather station which added wind, temperature, atmospheric pressure and 3D attitude.

This required new SignalK interface technology to replace the old NMEA-0183 traditionally used over WiFi.

SignalK became a springboard into some really useful capabilities.

I will describe what we’ve done, and what it cost.

You can stop anywhere along the process but the further you go the better the capabilities, and the value of the investment!

Electronics: Gathering the Data

When contemplating upgrades we keep in mind our prioritised data list:

  • Position (from GNSS systems – GPS, Galileo, Glonass, collectively ‘GPS’)
  • Water depth n Boat speed and heading
  • Speed and course over ground (SoG and CoG)
  • Autopilot n Communication (VHF plus SSB and/or Satphone)
  • AIS transceiver
  • Wind sensor (apparent wind)
  • Environment sensor (atmospheric pressure, air temperature, attitude)
  • Radar

The autopilot is important enough for us to have two fully installed and calibrated units.

Radar is last since AIS pushed it down the list.

We had radar but it failed years ago.

A replacement hasn’t made the cut yet and we’ll ignore it here.

We’ll also ignore SSB and satphones.

Recognising that AIS transceivers integrate GPS we can translate the data list into a list of system elements:

  • AIS (position, time, SoG, CoG, traffic)
  • Thru-hull sensor (boat speed, water depth, water temperature, 3D attitude)
  • Autopilot (heading, rudder angle, route-related data, 3D attitude)
  • VHF (DSC messages)
  • Wind sensor (apparent wind)
  • Environment sensor (atmospheric pressure, air temperature, 3D attitude)

It’s interesting that 3D attitude is appearing in so many sensors.

The technology is now very cheap and easy to integrate into products.

A weather station for a boat

A more expensive weather station, with ultrasonic wind sensor, gave Mike the full range of data he wanted. Credit: Mike Reynolds

Our research revealed the availability of NMEA-2000 weather stations.

These integrate high-speed GPS and measure apparent wind, ground wind, air temperature, atmospheric pressure, 3D attitude and more.

No moving parts. It gave us all the environmental data we wanted and addressed a desire for GPS redundancy.

So our list became:

  • AIS transceiver (about £800)
  • Thru-hull sensor (about £300)
  • Autopilot (about £1,300 tiller, about £2,500 wheel)
  • VHF transceiver (about £300)
  • Weather station (about £1,500)

All of these system elements are readily available with NMEA-2000 interfaces.

The total cost is under £5,000 for tiller and £6,000 for wheel auto-pilots including cabling and mounting gear.

To save £1,200 the weather station could be replaced with a wind sensor (about £300).

We valued GPS redundancy and environment data highly so installed the weather station.

Displaying the Data

Marine MFDs (Multi-Function Displays) and chartplotters are nice.

Many boats have two. But they’re not cheap, and nor are charts for them.

We fitted a small one soon after purchasing Zen Again, and carried a spare.

A MFD mounted in the cockpit of a boat - some of the electronics needed to receive navigation data

A cockpit-mounted tablet provides MFD functions using SignalK. Credit: Mike Reynolds

As time passed one failed and the other was relegated to data display only.

Five years ago we started chartplotting and displaying data on laptops and tablets.

This change was enabled by the WiFi access point on our AIS transceiver.

This, together with the integrated GPS, makes the AIS the heart of the system.

Continues below…

It broadcasts its own data plus other data from the NMEA-2000 network.

We’ve crossed three oceans and circumnavigated the UK using only laptops and tablets for chartplotting and data display.

They’ve survived storms and a lightning near-miss which destroyed a marine-standard interface unit and damaged one of our autopilots.

With his new SignalK system for £200, Mike no longer needs an array of expensive standalone electronics at his chart table

With his new SignalK system for £200, Mike no longer needs an array of expensive standalone instruments at his chart table. Credit: Mike Reynolds

We carry fully configured spares.

With thunderstorms nearby we disconnect all their cables to minimise risk.

The apps we use are OpenCPN on the laptops and iNavX on the tablets.

OpenCPN is a free, open-source, full-featured chartplotter.

On OpenCPN we use ooSENC charts supplemented by satellite imagery.

iNavX is also an excellent chartplotter and uses Navionics charts.

We like the redundancy of multiple chart sources.

Both apps support display of real-time instrument data.

Most marine WiFi access points broadcast data as a NMEA-0183 datastream.

This limits the data to that supported by NMEA-0183. This was a serious problem in our latest upgrade which added the weather station.

Much of the new data is unsupported by NMEA-0183.

More research suggested SignalK was the answer.


SignalK is a free, open source marine data exchange format.

It provides a means of sharing marine data in a future-proof manner friendly to WiFi, mobile networks and the internet.

The heart of SignalK is a software server which inputs and outputs NMEA-0183, NMEA-2000 and other data streams.

The software translates the data streams to and from SignalK format and makes the SignalK data available to client apps.

Clients can be on the same computer or on other connected computers.

Each client gets only the data it requests.

Client apps can be on phones, tablets or laptops, aboard or elsewhere.

The only additional hardware required is a NMEA-2000 USB gateway for about £150. An example use of SignalK is the open source system OpenPlotter.

OpenPlotter uses a £50 Raspberry Pi computer to run SignalK and OpenCPN, providing a full onboard MFD solution, albeit not to ‘marine standard’.

SignalK supports more than described below, including monitoring and controlling devices, and generating alarms.

Cheaper electronics onboard, like a BeagleBone computer can help you get the latest tech on your boat at a fraction of the cost

A simple, cheap computer runs SignalK and records all NMEA2000 data. Credit: Mike Reynolds

On Zen Again we already had several BeagleBone computers aboard.

They’re less capable computers than the latest Raspberry Pis but consume less power.

We decided to try SignalK on one of them.

We purchased an Actisense NGT-1 NMEA-2000 USB gateway and set to work installing the SignalK software on the BeagleBone.

Installation wasn’t simple but it’s now documented on our blog.

OpenPlotter comes with the software pre-installed for a Raspberry Pi. Our experiment has worked out very well.

The Beaglebone now feeds SignalK over WiFi to OpenCPN on our laptops and to client apps iNavX and WilhelmSK on our laptop, tablets and phones.

A SignalK gateway opens up a whole range of real time and historic data tracking, giving a more informed picture of how conditions are changing.

A SignalK gateway opens up a whole range of real time and historic data tracking, giving a more informed picture of how conditions are changing. Credit: Mike Reynolds

It also transmits wired NMEA-0183 to our old autopilots.

We also have all the software installed and configured on a spare BeagleBone.

Both hardware and software have proven to be very reliable after several months of 24/7 operation.

WilhelmSK is a £20 SignalK client app which runs on iOS and MacOS.

It supports user-designed pages to suit your data and also your current situation.

For example we have sailing, anchoring and weather pages.

Beyond SignalK

With SignalK proven aboard we looked at what more we could do with our data.

We like to record our passages, which previously amounted to written hourly logs and electronic GPX files of our tracks.

SignalK supports output to the free database software InfluxDB.

InfluxDB was simple to set up on the BeagleBone.

This records all of our NMEA-2000 data, giving us a ‘black box’ recorder.

To view recorded data we installed the free graphing software Grafana on our navigation laptop.

The laptop accesses the BeagleBone’s InfluxDB database over WiFi.

Electronics engineer Mike Reynolds

Mike Reynolds is a consultant electronics engineer who occasionally lectures on yacht navigation and communications systems. Credit: Mike Reynolds

We created Grafana ‘dashboards’ to display our data.

While sailing we can view trends like speed, wind, current, atmospheric pressure and so on.

After passages we can capture summaries and highlights.

WilhelmSK can display web pages, including Grafana dashboards.

SignalK has given us a lot of information and enjoyment for the £200 hardware cost of a BeagleBone and an Actisense NGT-1.

Most of the software for these programmes is free.

Installing the software wasn’t trivial but it put the future of marine electronics on our boat today.

Adding recorded data display to real-time data display is certainly a plus.

Electronics gear

Actisense NGT-1 NMEA-2000 USB gateway

Actisense NGT-1 NMEA-2000 USB gateway

Buy it now on eBay (UK)

Buy it now on eBay (US)

Raspberry Pi 4 Model B 2GB Quad Core 64 Bit Cortex-A72 4x USB WiFi Bluetooth 5 (2GB)

Raspberry Pi 4 Model B 2GB Quad Core 64 Bit Cortex-A72 4x USB WiFi Bluetooth 5 (2GB)

Buy it now on Amazon (UK)

Buy it now on Amazon (US)

BeagleBone Black

BeagleBoard Black

Buy it now on eBay (UK)

Buy it now on eBay (US)

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