Most people are familiar with using a sat-nav for navigating in a car.
What is slightly less familiar, however, is whether you can use that same system for navigating a boat.
As it happens, the answer is a little more complicated than simply saying yes or no.
You can use a car GPS to navigate on a boat, but not on its own. A car GPS will give you a position, but it will not give you any information about underwater hazards, traffic separation schemes or other maritime navigational information.
When discussing a car GPS, most people are actually referring to a car’s Sat-Nav system.
The system is often pre-installed in your car or it is possibly a removable unit stuck to your windscreen.
GPS is just a technology inside a car’s Sat-Nav.
That same GPS technology is found inside maritime electronic navigation systems such as Chart Plotters, or an ECDIS.
GPS gives you your position, which is then fed into whichever type of navigation system you are using.
In a car, positional data from the GPS is fed into an electronic map containing streets and addresses.
On a boat, similar positional data is instead fed into an electronic chart containing maritime navigational information like water depths and underwater obstructions.
Alternatively, some GPS systems just give you the raw positional data and you then need to plot it on either a paper chart or a map.
Used in this way, when you are given the raw data, a car’s GPS could be used to get your boat’s position for you to plot on a paper chart.
What type of GPS do boats use?
Boats use two different sorts of GPS. Regular GPS, and Integrated GPS.
Regular GPS is used to give you raw data such as your position, course over ground, and speed over ground.
It is often found on older vessels that have not upgraded to modern Integrated systems.
Data from Regular GPS needs further interpretation to be able to navigate effectively. For example, it could be plotted on a paper chart.
Integrated GPS is found on more modern vessels, and is an upgraded version of Regular GPS.
It effectively just takes a raw GPS feed and plots it onto an electronic chart.
Examples of Integrated GPS systems include Chart Plotters, ECDIS, or a mobile phone running a Chart Plotter app.
Integrated systems all rely on storing and processing hydrographic data so that they can display accurate navigational charts in addition to GPS data.
What is the difference between a car GPS and a boat GPS?
The actual GPS system used by cars and by boats is the same.
They both use the same satellites, controlled by the same ground stations, feeding data to the same receivers.
The difference between a car’s GPS navigation system and a boat’s GPS navigation system is how it displays that data to the user.
In a car’s GPS, the user is shown a digital version of a road atlas, with the car plotted in the correct position.
The user can see all the roads surrounding their location so that they can navigate efficiently.
In a boat’s GPS, the user is shown a digital version of a nautical chart, with their vessel plotted in the correct position.
The user can see all the navigational hazards, water depths, and aids to navigation around them so that they can navigate efficiently.
How can you use a car GPS on a boat?
If you use a car’s GPS on a boat, it will still show you your position, but you will just appear to be in a plain blue expanse of water, void of any navigational features.
In order to use your car’s GPS on a boat, you will instead need to extract the raw positional data.
Within the menu, you should find an option to display your latitude and longitude.
Your latitude tells you how far North or South you are, and your longitude tells you how far East or West you are.
You then take your latitude and longitude and plot it straight onto a paper nautical chart.
Nautical charts are marked with latitude and longitude along both edges, so it is a simple process to transpose your position onto the chart.
Once plotted, you can then identify navigational features in your location so that you can navigate safely on the water.
Plotting a second position at a set time interval after the first can even be used to calculate your speed.
Car GPS systems can be used to navigate on a boat. You just need a way of interpreting the data to make it useful for navigation.
Are there GPS systems that will work in a car and on a boat?
The most common GPS nowadays is actually the one in your mobile phone.
Your mobile phone is capable of acting as both a car GPS or a boat GPS.
To use it as a car GPS, most phones come with a maps app. Regular map apps are great for use on roads, but they do not have any maritime navigational information.
To use your phone as a boat GPS, you can download a dedicated nautical charting app instead.
Searching in app stores will reveal a whole selection of different chart plotting apps that you could use.
My favourite one is Navionics, which displays charts as well as your own position, course and speed.
You can even plan passages as a series of waypoints, and the app will act in the same way as a car’s satnav, guiding you to your destination.
I recently tested a whole selection of different chart plotting apps, so you should check out that article to see the range that is on offer: Top 8 Apps For Marine Navigation (Judged By A Navigator)