Marine navigation apps for a tablet or mobile phone are a relatively recent innovation.
Not only did the technology need to be sufficient to be able to process the vast quantities of data from nautical charts, but connectivity needed to be developed so that the apps could actually receive useful information to process.
So, now that they are here, how exactly do they work?
Marine navigation apps work by combining raw vector chart information with navigational data from your boat’s instruments, and user-generated data in the form of routes and tracks. They then display it in a way that navigators can interpret as useful navigational information.
The first part of any navigational app is the underlying chart.
The chart is the foundation of the app, containing a full database of maritime navigational information such as buoys, lights, depths, contours, coastlines etc.
Once the app is able to display the chart, the next thing that is needed is navigational inputs to be able to add useful information to it.
Apps usually only need a position input from GPS to be able to function. It could be your device’s internal GPS, or it could be an external Bluetooth model.
If you use your boat’s NMEA network to source a GPS feed, it is possible to send a whole host of other data to the app as well.
The app will take any data that is sent and use it to form a useful output. Most commonly, it will plot your position on the chart, but it might also display things like the UKC, wind speed or direction, or even information about your fuel consumption.
The third element of a navigational app is user-generated data. This includes things like routes that you draw onto the chart. The idea is that following a pre-planned route will keep your vessel safe.
The app processes its navigational inputs and uses them to plot your position relative to your pre-planned route.
It can show you if you are on track, or even tell you the course and distance to the next waypoint, assisting your navigation along the way.
The whole idea of navigation apps is that they can process and display a great deal of data to help your decision making while navigating.
They are not a replacement for traditional navigational techniques, but they can be a great aid.
Marine navigation app charts
Underpinning the entire app experience are the charts.
Most apps use vector charts which are basically just a database containing positions and information about every charted feature.
It could be depths, or coastlines, or buoys, or lights etc.
For example, a sounding will contain the position of the sounding as well as its value.
The app processes the database of information and displays it to the user in a visual way so that it looks like a nautical chart.
As the data is built onto the screen by the app, you get a great deal of control in terms of the layers that you wish to display.
If your screen is getting too cluttered, you can switch off “layers” of data, keeping only the most relevant information on your screen.
Not all apps use vector charts, however.
Some use raster charts instead.
A raster chart is just a scan of a paper chart, displayed on a digital screen.
Raster charts will often be “quilted” which means the app will stitch them together in such a way that you can seamlessly scroll across the view.
As you zoom in, a quilted chart will pull up different charts corresponding with different levels of detail.
The main problem with raster charts is that there is no underlying database to interrogate to find additional information about any given point on the chart.
You could be zoomed in on one spot, and completely miss a note that is written in a different part of the chart warning you of danger.
For this reason, the majority of charting apps available will use vector charts.
Marine navigation app data inputs
To be able to use your chart app for navigation, you need to feed navigational data into the system.
The most basic type of data is your position.
Navigational apps use a GPS feed for a position, either from an internal GPS, Bluetooth GPS, or GPS feed through a NMEA network.
Regardless of the source, a GPS feed allows the app to plot your position at any given time.
Continuous monitoring of your position then tells the app both your speed and your course. These are often displayed on the screen as a vector.
If your app has a NMEA interface, it is possible to feed in any other data flowing around your boat’s network.
For example, some will display the depth of water under your boat, and others will show you the wind speed and direction from your anemometer.
It can even show other vessels on the app by taking an AIS input.
Different apps are capable of accepting different data feeds. If you want to see almost every possible feed, I recommend iNavX as a great app. It is highly customisable and able to display more data types than any other app that I have found.
Marine navigation app user-generated data
With the underlying chart and navigational data feeds in place, the only thing remaining is to have a plan of where you are going.
With navigational apps, your passage plan involves drawing a route on the chart, following a safe passage from your origin to your destination.
The idea is that with a proper track planned, you can just follow the track and you know your vessel will be safe.
Passage planning generates a great amount of user data for your app to display and monitor.
Routes are the most common thing to plan, but you can also add user-generated data in the form of notes, no-go areas, parallel index lines etc.
Different apps allow different amounts of user-generated data, so you can check out different ones to make sure you find one that will do what you need.
Marine navigation app passage monitoring
The final step in understanding marine navigation apps is to understand how they use all their data and inputs to help with navigation.
Usually, user-generated data will be overlaid on the nautical chart so that you can see both at the same time.
The navigational inputs are then used to plot your boat’s position and monitor progress along your pre-planned route.
With the route known, the app can supply you with additional information to assist with your passage.
It can tell you the range and bearing to the next waypoint, so you could make your way straight there.
It can also tell you the total distance left on your passage, and give an estimated time of arrival at the end of the route.
Every app allows you to monitor your passage differently.
My personal favourite is Navionics because it displays just the right amount of data, in an incredibly user-friendly way.
You can read my full Navionics review here: Navionics App Review.