Getting the Most From The Marine GPS System

At the heart of modern marine navigation is the Marine GPS System, which is a network of 24 dedicated Global Positioning System (GPS) satellites spread out in geo-stationary orbit some 20,000km (12,500 miles) above the earth.

As the earth rotates below, at least four of the satellites are above the horizon at any one time and 'visible' from anywhere on earth.

Each of these navigational satellites knows precisely where it is, and kindly broadcasts this information at very accurately predetermined times.

The active antenna of our marine GPS system records the times taken for the transmissions to reach it and computes a three dimensional fix in terms of latitude, longitude and altitude to a high degree of accuracy.

But there's a lot more functionality to satellite navigation than position fixing...

What the Marine GPS System Can Do

As long as you give it a clue as to your intended route by entering a start and a destination waypoint, along with as many intermediate waypoints as may be required your GPS unit can perform a number of other useful tricks, including displays of:

Course Made Good (CMG) - the bearing from the starting point to the current position;

Cross Track Error (XTE) - the distance off either side of the desired course, often shown on a 'rolling road' graphic;

Estimated Time of Arrival (ETA) - the date and time of arrival at the destination based on current speed over the ground;

Estimated Time on Route - the time to go to arrival at the destination based on current speed over the ground;

Ground Speed - the velocity in knots relative to the sea bed;

Velocity Made Good (VMG) - the closing speed towards the destination.

The system goes beyond assisting with navigation—it also works as a vigilant safety tool.

Be Alarmed!

Your marine GPS unit can be a lifesaver, thanks to its alarm features. These alarms can notify you when:

Your anchor drags. This one will really get you out of your bunk in a hurry;

The cross track error exceeds a preset distance;

You approach your destination or an identified hazard such as a reef or shoal;

The GPS loses its fix.

Additionally, every GPS set includes a dedicated Man Overboard (MoB) button. Pressing this immediately records the current position and displays the quickest route to return to the point of activation. Advanced systems also integrate with distress signal technologies, ensuring your position is communicated to rescue authorities swiftly.

A Handheld Marine GPS Unit or a Fixed Unit?

Both handheld and fixed GPS units have their advantages. Handheld units are prized for their portability and reliance on replaceable AA batteries, making them great for small boats or as emergency backups.

Fixed units, on the other hand, draw power from your boat’s 12v supply and feature larger, easier-to-read screens. For most sailors, the best approach is to carry both: a reliable fixed unit for regular navigation and a handheld unit stowed in an emergency grab bag.

Beyond these choices, today's GPS units are equipped with cutting-edge technologies to make navigation even easier and safer.

A Fixed 'Standalone' GPS Unit

Integration with Other Systems

Modern marine GPS units often integrate with radar, sonar, and Automatic Identification Systems (AIS) to provide a comprehensive picture of your surroundings. For instance, AIS displays real-time details of nearby vessels, while sonar data can map the seabed to help you avoid underwater hazards.

High-end systems also include real-time weather overlays, offering insights into wind patterns, storm activity, and tide conditions. Combined with bathymetric data, these features allow for more informed route planning.

Additionally, many units now support autopilot integration, enabling your boat to follow pre-set routes without constant manual input—an invaluable feature during long passages.

Advanced Features

Some of the latest GPS units feature augmented reality overlays, which superimpose navigation data directly onto real-world views. This innovation helps you see waypoint markers, potential hazards, and port entries in context, making complex navigation more intuitive.

Wireless connectivity and cloud integration are also transforming marine navigation. With these features, you can sync routes across devices, back up data, and download software updates seamlessly. This connectivity even enables sharing routes with crew members or accessing them from remote locations.

Practical Tips...

To ensure your Chartplotter/GPS unit remains reliable, keep its software and charts updated. Outdated systems might not account for changes like newly marked hazards or updated port layouts. Regular maintenance, such as cleaning connections and ensuring firmware is up-to-date, will extend the device’s life and maintain its accuracy.

Security & Safety Enhancements

As technology advances, so do risks like GPS spoofing and signal jamming. To mitigate these threats, modern units are equipped with PIN-protected anti-theft features and even algorithms designed to detect and counteract spoofing. When choosing a GPS, prioritize models with robust cybersecurity features.

In terms of safety, ensure your unit integrates seamlessly with emergency systems like Global Maritime Distress and Safety System (GMDSS). Conduct regular drills to familiarize your crew with functions like the MoB button or distress signal activation.

The Future of Marine GPS

Emerging technologies are pushing the boundaries of marine navigation. Artificial intelligence, for example, is being used to optimize routes based on real-time data, including weather and traffic conditions. New satellite constellations such as Galileo and BeiDou are being integrated into marine GPS systems, offering better accuracy and redundancy alongside traditional GPS networks.

In the coming years, innovations like satellite-based Internet of Things (IoT) networks could allow your GPS unit to monitor onboard systems remotely, further enhancing efficiency and safety.

Bringing It All Together

The marine GPS system has come a long way from its origins as a basic position-fixing tool. By combining advanced features with a commitment to safety and environmental responsibility, today’s GPS units offer a comprehensive solution for sailors of all experience levels. Whether you’re navigating coastal waters or crossing oceans, a modern GPS system is an indispensable part of your maritime toolkit.

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