Wireless NMEA2000 on OpenCPN


Slowly but surely, NMEA2000 the latest marine electronics networking standard is making its way on to boats; old and new. With most new marine electronics equipment having an NMEA2000 interface, we are seeing more and more requests for our NavLink Wireless NMEA2000 Server, that allows you to wirelessly send NMEA2000 data to phones, tablets and computers.

Although there is some initial investment required to purchase and install an NMEA2000 “Backbone” (the T-Pieces, terminator resistors and cables) once you have your basic network setup adding extra equipment is very quick and easy. Just today we had a customer who phoned us concerned about how to install a new AIT2000 Class B Transponder and one of our NavLinks on to his new boat that already had an NMEA2000 network installed. The customer had never seen the “backbone” and had expected to need all sorts of tools, crimps, soldering iron, etc. He was very pleasantly surprised to discover that both units just plugged in to the network and the NavLink even took its power from the NMEA2000 bus.

NMEA2000 Backbone

It turned out that the customer was a big Apple fan and wanted to use all of the NavLink’s wireless NMEA2000 data in OpenCPN running on his Mac and maybe later on to purchase a suitable app to run on his iPad. With everything connected up, it was a simple matter of scanning for wireless networks on his Mac and connecting to the NavLink.

Then in OpenCPN, we got him to go to settings, select connections and click on the “Add Connection” button. Then in the connection properties section select “Network”, Protocol = UDP (so that multiple devices can receive the same data), Address = and Port = 2000 (as shown below).

OpenCPN Connection Mac

Once the connection settings were entered, it was just a case of clicking the “Apply” button and then the “OK” button to establish the data connection to the NavLink and the GPS and AIS data started to stream in from the AIT2000 AIS Class B Transponder.

OpenCPN AIS on Mac


Our customer was extremely happy that everything was so easy to install and setup and is now looking at installing the Dashboard or NMEA Instrument Plugins for OpenCPN so that he can use more of the NMEA2000 data available on the network.

By selecting the broadcast UDP mode (rather than TCP)  in the connection to OpenCPN, it means that he can simultaneously get the same data on his iPad, when he decides what App to get.

Permanent USB Connection to our AIT2000


Our AIT2000 transponder comes complete with a useful USB connection that allows you to quickly and easily configure the unit using our proAIS2 software. Once configured, there is no need to use the proAIS2 software again, other than perhaps to check the AIT2000 at the beginning of the season to ensure it is operating correctly.

A number of customers have also used this USB connection to permanently connect our AIT2000 to a PC or Mac, so that they can display the AIS data on suitable navigation software. For the majority of customers this works perfectly fine, but you need to be careful with your installation as the USB interface is designed to link consumer products.

The problem appears to be that the microprocessor’s USB interface can be damaged by static discharge (in lightning storms) or grounding differences between the boat’s electrical system and the PC/Mac power supply which is often AC powered or via a DC-DC converter.

In these situations, the ground connection in the USB cable can see high surges in current/voltage that can damage the microprocessor and to avoid this, we recommend that any customers who will be connecting the AIT2000 permanently to a PC or Mac, should use one of our NMEA to USB Adaptors (see image above) to provide an extra level of protection.

The part number of the adaptor is ZDIGUSBNMEA and below is a diagram showing how it can be connected to the AIT2000.

AIT2000 NMEA Connections to USB Adaptor


CPA and TCPA Alarms Explained

AIS CPA Alarm Indicators

One of the best features of the Automatic Identification System (AIS) is the ability on some chart plotters or navigation software to set alarms that warn you if and when you will get too close to another vessel. These collision avoidance alarms are a godsend and can save you so much time and stress when navigating across a shipping lane or in bad weather.

There are basically two alarms; Closest Point of Approach (CPA) and Time to Closest Point of Approach (TCPA). Most systems will allow you to enter your own CPA and TCPA values for when the alarm will be triggered and so you need to decide how close you want to let other vessels get to you (CPA) before an alarm sounds and also how much time you need to take avoiding action (TCPA). For instance, you might decide that 0.25NM is plenty close enough for large vessels to pass by you and you want to have 15 minutes notice so that you have time to take avoiding action and/or call them on the radio.

The image below shows the “imaginary” guard zone around the yacht that is set by the CPA alarm value (in this case 1NM) and also the distance the fast moving powerboat will be when the TCPA alarm goes off 5 minutes before the CPA situation occurs.


Prudent use of the CPA and TCPA alarms will definitely make your voyages safer, but do familiarise yourself with how your particular system works and know how to turn off the alarms when you are approaching busy harbour entrances and rivers, otherwise they will keep going off and drive you crazy !





ISAF Offshore Special Regs now mandate an AIS Splitter


An important change to AIS installations has now come in to effect for Mono and Multi-Hull Category 0, 1 and 2 offshore racing yachts. The new 2014-2015 International Sailing Federation (ISAF) Offshore Special Regulations (click here to download), that became effective as of 1st January 2014, include an important note that all AIS antennas (VHF not GPS) must now be fitted to the top of the mast.

Due to space and antenna separation issues (see previous post on this subject), it is not possible to have both a VHF and an AIS antenna mounted at the top of the mast, so in order to meet these new regulations, a yacht will need to fit a suitable antenna splitter. It is important that this splitter is suitable for use with an AIS Transponder and we would recommend one of the latest generation of “Zero Loss” splitters that do not attenuate the VHF Radio or AIS reception.

Our SPL2000 splitter is an ideal solution and can even be used with a Class A transponder, which Category 0 Mono and Multi-Hulls are required to fit. Installation is very straight forward (all of the cables are included) and the unit should be mounted close to the VHF radio and transponder.  

Once installed, the SPL2000 will automatically feed the received radio signals to both the VHF radio and the AIS. As soon as either the radio or AIS starts to transmits, the SPL2000 instantly disconnects the other device that is not transmitting. Priority is given to VHF calls and two LED indicators on the front of the unit show when either device is transmitting.

The benefit of using a splitter, and probably the reason for this change to the regulations, is that you get maximum AIS transmit and receive range. This is obviously important when racing offshore, and with the latest “Zero Loss” technology there is now no attenuation of the received signals, which traditionally has been the biggest dis-advantage of using a splitter.

Below is a wiring diagram showing how a splitter is connected to a typical AIS Class B transponder system.

Class B Transponder – Dedicated Antenna or Splitter ?


One of the most common questions we are asked by customers wanting to purchase an AIS Class B Transponder like our AIT2000, is what VHF antenna should they use ?

The AIS system, uses two special “Data Only” channels of the VHF frequency range to transmit and receive its packets of digital data. Therefore any VHF antenna can be used to receive and transmit AIS data and generally the same selection criteria, mounting advice and installation issues apply.

In an ideal world, to get maximum AIS reception, you would mount the AIS/VHF antenna at the highest point of the boat i.e. at the top of the mast on a sailing yacht or on the radar arch or flying bridge of a power boat. However, the VHF radio’s antenna is usually at this exact same location and you cannot have the two antennas within 2m of each other, otherwise all of the 25W transmit power of the VHF antenna will go straight in to the receiver of the AIS and damage it. See our previous post on antenna separation by clicking here.

On a power boat, you might be able to get away with having the VHF antenna on one side of the boat and the AIS antenna on the other side (depending upon the boat’s beam) and on a ketch/schooner you have the luxury of two masts and can mount the VHF antenna on one and the AIS antenna on the other. However, for the majority of yacht owners, who already have their VHF radio antenna at the top of the mast, they have to make a decision between;

1) Fitting a dedicated antenna for the AIS in another location on the boat


2)  Use a “splitter” to allow both the AIS and Radio to share the VHF antenna

Splitters have been around for some time and prior to AIS, splitters would be used to allow an AM/FM radio to share the VHF antenna. When the first AIS receivers were launched, many yacht owners used a splitter to allow the AIS receiver and the VHF to share the same antenna. Although this made installation quite easy, the traditional splitter was a fairly crude device that simply split the signal from the antenna – half of the power going to the VHF and the other half to the AIS. This meant that many yachtsmen, who went to a lot of trouble to fit a good quality VHF antenna at the top of the mast to get maximum VHF range, now found that their VHF reception range was significantly reduced after fitting the splitter.

For this reason, Digital Yacht have traditionally recommended the use of a dedicated AIS/VHF antenna for connection to their AIS units. Ideally this would be mounted as high as possible, for instance on an antenna bracket at the stern of the boat or, space permitting, on the spreaders. Failing this, the dedicated antenna can be mounted at deck level on the stern rail and still provide reasonable reception of the large ship Class A transponders – typically 10-15 miles. It is important to also note that Class B transponders only transmit at 2W so even with a perfect antenna installation at the top of a mast you can only really expect about an 8 mile transmit range – mounting on the stern rail will probably reduce your transmit range to 4-5 miles.

Another consideration of using a dedicated VHF/AIS antenna, is that with a bit of thought during installation, it can double as an emergency VHF antenna. If you keep the necessary adaptor (usually PL259 to BNC) then in the event of your main VHF antenna failing or a demasting, you can quickly unplug the AIS antenna and plug it in to the VHF radio.

You have to weigh up the cost/time of installing a dedicated VHF/AIS antenna versus the cost of a splitter. Our GV30 combo GPS/AIS antenna (see image above) helps to make installation easier by having just the one antenna to find a location for and slim FME type connectors on the two cables, to make routing the cables through the boat easier. On smaller boats the GV30 is an ideal antenna for any Class B transponder and is becoming a popular option with our AIT2000 transponders.

So why would you fit a splitter ? Well unlike the traditional splitters, our latest SPL2000 splitter uses a new “Zero Loss” technology that boosts the received signals prior to splitting them. This results in no loss of reception on either the AIS or VHF and for the first time yachtsmen can have a simple easy to install splitter with no reduction in performance. By using the main VHF antenna at the top of the mast, you get maximum AIS performance and installation simply involves unplugging the VHF antenna from the back of the radio and connecting it to the SPL2000 along with the supplied cables that go to the radio and AIS. Mounted in the same matching enclosure as our AIT2000 transponder, the SPL2000 is the perfect solution for larger yachts and will work with any Class B transponder – not just Digital Yacht ones !

IMPORTANT NOTE -  a Class B Transponder needs a special type of splitter that has two intelligent switches inside that can detect either the VHF or AIS transmitting and in less than a few milliseconds disconnect the other device while the transmission takes place. Traditional lower cost (£50-£70) splitters only have one simple switch and should never be used with a Class B transponder

spl2000 copy-01

Connecting an AIS Receiver to an Android Tablet with Boat Beacon

Android Tablet

Today we finished a series of successful tests, connecting our AIS receivers to a Google Nexus 7 Android tablet. This was made possible by a new version of Boat Beacon the popular AIS App for Apple and Android devices, which should soon be available (as a free update) on the Apple Store and Google Play Store.

One of the most popular features of Boat Beacon was that it allowed you to receive AIS data on your phone or tablet (from the internet) without having to install an AIS receiver on your boat. What is more, you could also transmit your position (without having an AIS transponder), so that you appeared on AIS websites like Marine Traffic, Ship Finder and AIS Hub, allowing friends and family to track your passage. In order to receive AIS data and transmit your position, you needed to have a 3G internet connection, but for many people Boat Beacon was a great app to have and introduced them to the world of AIS.

Relying solely on Internet AIS data does have serious limitations though, namely;

  • Holes in the AIS network coverage
  • Slow update speeds
  • Constant risk of losing the 3G internet connection

This is the reason why most boat owners ultimately decide to fit an AIS receiver on their boat, but then you have the issue of getting this AIS data on to your phone/tablet. With Apple devices, currently the only option is to use one of our Wireless NMEA units to convert the AIS data in to wireless NMEA data that an App running on the iPhone/iPad can read. Many Apps including Boat Beacon support Wireless NMEA, which we documented in a recent article (click here to read it).

However, many Android devices now support USB “On the Go” (OTG) which allows USB slave devices to be plugged in – see USB OTG cable in image above. In order for the USB slave device to work correctly, Android must have suitable drivers installed and there must be an App running that knows how to use the USB device. As part of our testing, we confirmed that the drivers for all of our AIS receivers (and our NMEA to USB adaptor cable) are pre-installed in Android and that the latest Boat Beacon App will read the NMEA0183 AIS data and display the AIS targets on its chart display.

Installation could not be easier, simply plug in the USB OTG cable to your Android device, download the latest version of Boat Beacon and then plug the USB lead of one of our AIS Receivers in to the OTG cable. Android should detect the AIS device and ask you to confirm that you want Boat Beacon to use this device.


Then Boat Beacon should open and you should see the live AIS data starting to come in and be displayed on Boat Beacon.


With CPA and TCPA alarms, colour coded AIS targets and the facility to also transmit your position back to the internet AIS sites via 3G, Boat Beacon is the best AIS App for Android and now with the option of connecting our AIS receivers via USB or any of our AIS units via one of our Wireless NMEA adaptors (WLN10, NavLink, iNavHub, etc.) you have an app that can be seriously used at sea as an AIS display and alarm system.

For more information on Boat Beacon visit the Play Store by clicking here.

New Improved Marine Traffic AIS Service

New Marine Traffic

Marine Traffic, the popular live AIS website, has had a major upgrade. First released in 2007, Marine Traffic has grown to be the most popular vessel tracking service in the world, with a large network of contributors that have installed AIS receiving stations (like our AISNet product)  in their homes or offices.

During the past few months they have completed a full redesign of their website and mobile applications, with more data and many new features. A video that shows the new features can be viewed by clicking here.

While keeping the basic service free, they have introduced a number of paid plans, built for users that need to make intensive use of the system resources and wish to access the value-added services, such as:

  • SAT-AIS  –  Satellite AIS data for global AIS coverage, including mid-ocean vessel tracking.
  • Detailed Nautical Charts  -  global Nautical Charts for in-depth insight and situational awareness.
  • Export AIS data  –  Export data to CSV files directly from the website.
  • AIS API  –  Use MarineTraffic API data services to feed data directly into your applications.
  • Historical AIS data  –  Retrieve historical AIS data within the billions of position records archived from 2009 onwards.

For Professional users they can now offer extended fleet management and notifications, via email and SMS alerting services.

Anyone who has an office or home near the sea (with an internet connection) who would like to contribute to Marine Traffic can use one of our AISNet Base Station units, which are easy to install and configure and just need a network connection to your wireless router and an external VHF antenna (mounted as high as possible) to receive the AIS transmissions.  Contributors to the Marine Traffic network, get free access to many of the paid services and if your area is not that well covered, you will be helping the whole community in improving the network of receiving stations.

AIS + VHF Antenna Separation



The AIS system works on two channels in the VHF frequency range and in order to receive or transmit AIS information it is necessary for the AIS unit to be connected to a VHF antenna. One option is to fit a VHF splitter such as our SPL2000, which allows both the VHF radio and the AIS to use the boat’s main VHF antenna. The other option is to fit a second VHF antenna which is then just connected to the AIS.

Any VHF antenna can be used, although some antennas are “AIS tuned” to get maximum gain on the two AIS channels and also have a BNC type connector fitted (common on AIS units), rather than the traditional PL259 VHF connector.

If you decide to fit an additional VHF antenna for the AIS, you want to mount it as high as possible but you should be aware that it cannot be mounted right next to the existing VHF antenna and a certain amount of separation must be maintained to avoid the 25 watts of transmit power from your VHF radio going straight in to the AIS receiver circuitry, potentially damaging it. The diagram below shows the recommended minimum separation of the antennas.

Antenna Separation


Introduction to Marine AIS White Paper

AIS CPA Alarm Indicators

Although AIS has now been in use around the world for over 10 years, it is surprisingly difficult for anyone interested in AIS to piece together information about this important technology. Wikipedia has a pretty good article on AIS, but we felt it would be useful to take some of the training material we have used over the last few years and publish a White Paper on this interesting subject. If you are thinking about purchasing an AIS or are simply wanting to learn more about what AIS is and why it is an important aid to safe navigation, please click here to download a free copy of our Introduction to AIS White Paper.

Integrating a PC into your boat’s navigation system

Utilising a PC on board brings important benefits not just for regular PC tasks such as email and web access but also for entertainment and navigation.  This document explains how to integrate a PC into a boat’s navigation system and this approach offers substantial cost savings over buying a multi station traditional navigation suite.  PCs also provide a much more powerful platform and with an internet connection, data such as weather can be integrated into the system.  Navigation software for a PC is sophisticated yet easy to use.

Installed PC or notebook…

Whilst a laptop or notebook provides a solution to run e-navigation software, it’s not ideal.  Power consumption is high and often you will need an inverter or adaptor to connect to the boat’s DC supply which introduces more losses and electrical noise.  Notebooks don’t like the constant vibration and momentum from the boat and of course they’re not designed for salty air.  They also don’t have interfaces for the boat’s NMEA system so integration can be tricky.  We’ve found that most users trial a system with a notebook but move on quickly to a dedicated, installed system like our Aqua range of PCs.

Aqua PCs from Digital Yacht

Aqua 2 PC with Logos-web

The Aqua range of PCs from Digital Yacht are designed to be permanently installed and can connect direct to the boats DC electrical system.  They are capable of operation from 8-18V so can deal with a fluctuating battery supply.  They also consume minimal power (typically around 1A at 12V DC) and are completely solid state with no moving parts.  There’s no cooling fan to suck in moist air and the solid state hard drives offer exceptional reliability and speed.  They also feature a dual NMEA input to integrate straight into your boats navigation system.  Despite their impressive performance they are as affordable as a good quality laptop and can support multiple monitors.

Using the AIS transponder as the navigation feed…

If you’re contemplating a PC system then you’ll probably also look at having an AIS Transponder.  Our AIT2000 features a USB output to connect direct to an Aqua PC and provides a feed of AIS and GPS information.  It also incorporates a NMEA multiplexer so will take your boat’s instrument NMEA data and combine with the AIS data and output via USB.  One  connection to your PC with AIS, GPS and NMEA boat data!

Navigation Software for your PC…

One of the beauties of a PC based system is that you can constantly upgrade, change and evolve with the addition of new software.  Of course, we’d like you to use our SmarterTrack navigation package which offers great value for money, amazing charting capabilities and one of the best AIS presentations available today.  SmarterTrack uses Navionic’s charts and you’re now able to copy a Navionic’s chart (on SD or CF card – like the ones used on plotters such as Lowrance, Raymarine and Simrad) direct to you’re PCs hard drive – that means no duplicated charting costs!   SmarterTrack supports weather overlays, instrument displays and can be supplied with a NMEA 2000 interface

Add wifi internet access with the WL510…

Internet access afloat really adds to boating.  Not only can you keep abreast of news and email, but it’s a great source of entertainment, TV and media when in port.  It can also be used to dowload the latest weather information.  Free GRIB files are available to integrate with PC navigation programs to provide animated weather forecasts with wind, swell, pressure and temperature information.  Whilst on board, you can access the internet through 3G/4G systems, WiFi and satellite.  Digital Yacht make a range of high power wifi systems which offer easy and cheap data access with ranges of up to 5NM.  WiFi is cheap, global and fast and for many coastal sailors, it’s ideal.  Satellite provides a trans ocean solution but at a high price and substantial running cost.  The WL510 will integrate with your on board PC system to provide internet access

Fitting it all together

So here’s how it all interconnects.  In the cockpit or flybridge you can use any standard 5, 7, 10, 12 or 15″ multi function display/plotter, linking via NMEA direct to the Aqua PC system.  5″ plotters from Garmin, Raymarine and Lowrance offer incredible value for money, sunlight viewing capability and waterproof performance.  Even a 5″ screen is ideal for use by the helsman and if you choose a Navionic’s based plotter, you can share the charting with SmarterTrack on the Aqua PC.  Make sure your plotter choice accepts an AIS input too

In this system, we’ve added the WL510 for internet access, connected to our WiFi hub called iNavHub.  This allows internet data as well as navigation NMEA data to be shared with mobile devices such as iPads/Phones.

We’ve also utilised our SPL2000 VHF-AIS antenna splitter to share the VHF antenna with the AIS transponder and provide an aerial feed to an on board stereo.

Its a powerful system that offers incredible value for money