A phone is no longer just a phone. It is a very powerful handheld computer. You actually have more processing power in your pocket than you could find in the early moon landers.
It should come as no surprise that you can use your phone for pretty much anything, including marine navigation.
You can use a phone as a marine GPS, or even as a chart plotter, by simply downloading an appropriate app. Many free apps will turn your phone into a Marine GPS, and lots of paid apps will turn it into a sophisticated chart plotter.
The simplest conversion is to download an app that will display data directly from your phone’s GPS, effectively turning it into a Marine GPS.
A Marine GPS will give you basic data such as:
- Course over ground,
- Speed over ground,
- Distance travelled,
- Bearing to waypoint,
- Distance to waypoint.
The list above is not exhaustive, but you get the idea. A GPS gives you numerical information that you can use for navigation, but not enough to navigate on its own.
To navigate with a Marine GPS, you need to use it in conjunction with a nautical chart.
A nautical chart tells you about navigational features in your location such as water depth and underwater hazards.
Nautical charts are traditionally printed on large sheets of paper, but there is now a more modern equivalent. The electronic chart.
Electronic charts are integrated into many devices, one of which could be your mobile phone via a nautical charting app.
Used in this way, your phone becomes so much more than simply a Marine GPS. It becomes a chart plotter.
Chart plotters combine the data from a GPS with information from a nautical chart, automatically plotting your position on a detailed map of your vicinity.
With a chart plotter, you can navigate.
You are now left with a choice. Do you want your phone to be a Marine GPS, or do you want your phone to be a Chart Plotter?
What does a Marine GPS do?
A Marine GPS is an independent receiver fitted to a boat that can detect signals from GPS (American) satellites. Modern marine GPS receives will also detect GLONASS (Russian), Galileo (European) and sometimes BeiDou (Chinese) satellites in addition to GPS.
The Marine GPS can be integrated into a boat’s systems to provide a data feed, or it can be used independently.
When I started navigating at sea, a GPS would be a completely independent device that you could use to read your latitude and longitude, see your ground speed, or set a series of waypoints.
The other crucial feature of a Marine GPS is that it will tell you its accuracy, as well as information about the signal.
For example, it will tell you the number of satellites that it is currently tracking, as well as its HPOD (Horizontal Dilution Of Precision) value.
In this respect, you can quite easily use your phone as a boat GPS because there are plenty of free apps that you can download that will give you the necessary information.
Best free marine GPS apps
A quick browse in the App Store or Google Play will quickly show you plenty of options.
When you are looking for a GPS app, you can find plenty of free options, so you can try out lots of them and see which one you like.
A few of my favourites include:
Developer: Propane Apps
GPS Data is an excellent GPS app that gives you information about all the satellites that you are currently tracking, as well as the expected accuracy of your position.
Its information screen gives you all the data you need for navigation including your speed, course, and position.
There is minimal other functionality, but it is one of the best apps that I have found for simply translating GPS data into a usable format.
Mariner GPS Dashboard & Recorder – RAMS Mariner
Developer: Watch & Navy Ltd
I like Mariner GPS because of its simplicity. You open the app and get a speed dial in knots, and the ability to log your trips.
Making a log entry records your position and time as well as lots of optional things like the weather, distance travelled, visibility etc.
The key thing is that you can take the latitude and longitude from the app’s logbook and plot it directly onto your nautical chart.
SailFreeGPS is a great GPS app that is automatically set up for maritime navigation, with coordinates in a plottable format and your speed in knots.
The main screen tells you your speed over ground, course over ground, and your position. Supplementary screens can be used for tracking waypoints.
From the main screen, you can immediately take your latitude and longitude to plot directly on a nautical chart.
Nautical Nav: Free Boating & Sailing Navigation
Nautical Nav is a little different to the other GPS apps in that it primarily plots your position on map. It does, however, still give you GPS information as a small overlay at the top.
The map itself is not very useful because there is minimal navigational information, but you can use it to get a general idea of where you are.
Otherwise, you take your latitude and longitude from the overlay and plot it directly onto a nautical chart.
How do you use a GPS on a boat?
To use a GPS on a boat, you only really need the latitude and longitude.
The latitude tells you how far north or south you are from the equator, and the longitude tells you how far east or west you are from the Prime Meridian.
Most nautical charts are plotted using the same coordinate system that GPS uses, so you can plot your position directly on the chart.
Up the side of the chart, you have the latitude scale, and along the top and bottom, you have the longitude scale.
You just need to directly match the GPS position to the scales on your chart. The point where they intersect is your position.
Pro Tip: Check that your chart datum is WGS84, the same as the GPS datum. Occasionally charts are plotted using a different datum, which means you need to convert your GPS position to the chart’s datum before plotting.
Can you use a GPS instead of a marine chart?
A GPS cannot be used instead of a marine chart, but they can be used together for navigation. The GPS tells you your position, which you then plot on a marine chart.
Confusingly, when a lot of people say “GPS” they actually mean “chart plotter”.
A chart plotter is not the same as a GPS. You can use a chart plotter instead of a marine chart because chart plotters contain an integrated electronic chart.
A chart plotter is an electronic system that combines the functions of a GPS and a marine chart into a single device.
Chart plotters can be used for maritime navigation on their own.
What does a chart plotter do?
A chart plotter performs the same functions as a marine GPS, but it also has an integrated electronic nautical chart. On a chart plotter, your GPS position will be displayed on the digital chart, enabling you to follow electronic tracks that you program into the system.
Chart plotters are primarily a digital version of a paper chart, which has the functionality to accept positional data from external (or internal) sources such as GPS.
Modern chart plotters display vector charts, which are just a database of maritime navigational information. The chart plotter interprets the data and shows it to the user in the form of a chart.
On the chart, you can program a series of waypoints so that you will see a track to follow.
The GPS feed into the chart plotter allows the system to plot your own position with reference to charted objects and your own track. It can then tell you a whole host of navigational information such as range and bearing to waypoints, distance to destination, ETA at destination etc.
You will notice that most chart plotters show your course and speed on the chart by using a vector from your own vessel.
For example, a 3-minute vector will tell you where the plotter predicts your position will be in 3 minutes time.
As for your phone, in a similar way to using it as GPS, modern phones can also be used as a chart plotter.
All you need to do is to download an appropriate app.
Best marine chart plotter GPS apps
There are many different chart plotter apps available in the App Store, or on Google Play.
Most of the best ones are available cross-platform, so you can get the same functionality regardless of the device that you own.
The main difference between chart plotter apps and GPS apps is their cost, and that is primarily associated with licensing fees for the charts that they use.
Chart plotter apps take data gathered by national hydrographic organisations around the world and display it to their users.
The main exception to the pricing structure is in the USA. This is because NOAA charts are in the public domain, in the same way as other US Government works.
Other countries charge licensing fees for use of their data. For example, in the UK, the UK Hydrographic Office charges users to access the data they compile.
Once we accept that chart plotter apps will all have costs associated due to licensing the charts, we can compare to find which is best.
I’ll summarise them below, but if you want more detail I have compiled an entire article about the best chart plotter apps: Top 8 Apps For Marine Navigation.
Navionics is probably the most popular, and user-friendly chart plotter app that I have found.
With Navionics, you can automatically plot your position and follow tracks that you program in advance.
Due to its popularity, Navionics is an incredibly well-refined app, displaying all the data you need in an intuitive way.
It is currently my favourite nautical chart plotting app overall.
Read my full Navionics review: Navionics App: Reviewed By A Professional Navigator.
iSailor is the most sophisticated nautical chart plotting app that I have found. It doesn’t just turn your phone into a chart plotter, it almost turns it into a commercial navigation system.
Its passage planning functions come with advanced features that I have only otherwise seen on large ships.
The only problem with iSailor is that it is not as compatible as Navionics. It needs a very modern phone to be able to run.
Read my full iSailor review: iSailor: Reviewed By A Professional Navigator
C-Map is a great nautical charting app that offers incredible value for worldwide use.
The app comes with access to worldwide charts that you can browse, as long as you have an internet connection.
When you want to download them to use offline (necessary for boating), you pay a single subscription and you can download charts from anywhere in the world.
Read my full C-Map review: C-Map: Reviewed By A Professional Navigator.
iNavX is the most comprehensive nautical charting app available.
Its extensive features and customisation make it one of the more complicated apps to learn, but once you get used to it, you’ll be able to do so much.
I wasn’t particularly a fan of iNavX myself, primarily because it is so expensive for users outside of the United States.
In terms of app capability though, iNavX can do it all.
Read my full iNavX review: iNavX: Reviewed By A Professional Navigator.
Seapilot is one of my favourite marine chart plotter apps because the way it displays charts is so familiar to me.
I am used to using commercial systems on large ships, and the Seapilot app was the most similar-looking one that I found.
Its features are similar to all the other apps, although its menu system feels a little dated.
Read my full Seapilot review: Seapilot: Reviewed By A Professional Navigator.