GPS, Chartplotters, and VHF Radio: Understanding Modern Onboard Navigation

Hardly any modern sport boat goes without a GPS receiver, a chartplotter, or a VHF radio these days. These devices make boating more convenient and, in many situations, safer too. At the same time, they don’t replace the fundamentals you learn for the SBF See, Germany’s Sportbootführerschein für See, the required license for skippering sport boats above a certain size on coastal waters; instead, they build on top of them. This article explains how GPS, chartplotters, AIS, and VHF radio work together, where their strengths and limits lie, and how modern electronics fit sensibly into classic navigation.

Anyone who sees a chartplotter with its own position display for the first time quickly wonders why you’d still need a paper chart, a compass, and a pair of dividers. The answer comes down to reliability: electronics can fail, batteries can run flat, fuses can blow, and satellite signals can drop out when blocked. If all you’ve ever learned is to look at a screen, you’re left without orientation the moment that happens. If instead you know how to fix your own position using a chart, a compass, and bearings, you can always fall back on classic methods, no matter what the onboard electronics are doing. That’s why the same rule applies in practice as in the exam: modern navigation aids are a genuinely useful addition, but not a substitute for a solid grasp of the underlying navigation skills.

GPS stands for Global Positioning System, a satellite-based positioning system originally developed for military use and now freely available worldwide. A GPS receiver calculates your current position in latitude and longitude from the signal travel times of multiple satellites. On the water, GPS has long since become standard technology, since it works regardless of visibility or landmarks and shows your position accurate to within a few meters.

Position, Course Over Ground, and Speed Over Ground

A GPS receiver doesn’t just give you a raw position; from the change in position over time it also calculates two other important values: Course Over Ground (COG) and Speed Over Ground (SOG). Both differ from what you read off the compass and the boat’s speed log. The compass shows your heading, the direction the bow is actually pointing. Wind and current, however, can push the boat sideways, so the course you actually travel over the seabed, the course over ground, deviates from that heading. This drift is also covered as part of the navigation task in the SBF See exam. GPS shows you that drift directly, but it doesn’t replace understanding why it happens in the first place.

The WGS84 Reference System and Why It Matters

For GPS coordinates and a nautical chart to match up, both need to be based on the same geodetic reference system. Modern nautical charts and GPS devices today work by default with WGS84 (World Geodetic System 1984), so a plotted position will typically line up directly. With very old chart editions or charts drawn on a different reference system, however, a noticeable offset can still appear between the GPS position shown and the position plotted on the chart. Checking the chart margin for the reference system in use provides clarity before you blindly trust that the two will match.

The Chartplotter: The Electronic Chart in the Cockpit

A chartplotter links a GPS receiver to a digital nautical chart and displays your position directly on the chart image. That saves you the manual work of transferring coordinates onto a paper chart and gives you an immediately intuitive picture of your position, course, and surroundings. Many plotters also let you set waypoints and entire routes that you plan in advance and then follow on the water.

Fixed Plotters, Tablet Apps, and What to Watch Out For

Alongside built-in chartplotters, navigation apps on tablets or smartphones that work with electronic charts have also become established in recent years. Both variants follow the same basic principle as the paper chart: the same symbols for depths, shoals, and sea marks, just displayed digitally instead of printed. Once you’ve understood the logic of the nautical chart by working with it by hand, you’ll find your way around any plotter quickly, regardless of manufacturer.

One thing matters across all electronic solutions: chart scale. A chart image zoomed out too far can make smaller shoals or obstacles visually disappear, even though they’re actually plotted on the chart. A view zoomed in too far, on the other hand, shows too little of the surrounding area to plan ahead properly. For passage planning and ongoing checks underway, it’s worth actively switching the scale rather than staying at one fixed zoom level.

Staying Current and Keeping a Backup

Electronic charts need to be kept up to date just like paper charts: new wrecks, changed fairways, or newly placed sea marks are continuously published through Notices to Mariners (Nachrichten für Seefahrer, NfS) and need to be incorporated into the chart data. Anyone running outdated chart software risks missing important changes.

Because electronics can fail, whether from a flat battery, a blown fuse, or simply water getting into a housing, an up-to-date paper chart still belongs on board as part of a solid basic setup. It costs no time to reboot in an emergency and keeps working even if all onboard electronics go dark.

AIS: Seeing Other Vessels Before You Spot Them

The Automatic Identification System (AIS) is a radio-based system through which vessels automatically broadcast their position, course, speed, and further details such as name and vessel type. An AIS receiver onboard displays this information about nearby vessels, usually overlaid directly on the chartplotter. That’s especially valuable around larger commercial vessels: you can see early on what course and speed a cargo ship or ferry is approaching on, well before you could reliably judge that with the naked eye, particularly in darkness or reduced visibility.

There are plain AIS receivers, which only display signals from other vessels, and AIS transponders, which additionally transmit your own data and thereby make you visible to others too. One important point: a transmitting AIS transponder is a radio installation, and the same principles apply to operating it as apply to a VHF radio. If you want to know exactly which radio operator’s certificate is required for which cruising area, the details are covered in the article UBI or SRC – Which German Radio License Do You Need?.

Despite its advantages, AIS doesn’t replace keeping a proper lookout. Not every boat transmits an AIS signal; smaller sport boats without a transponder in particular remain invisible to you. AIS is therefore a valuable additional source of information, but not a complete picture of everything around you on the water.

VHF Radio: Standard Equipment With Its Own Certificate

A VHF radio is standard equipment on many boats, whether for communicating with other vessels, with locks and traffic centers, or, in an emergency, with search and rescue services. Unlike GPS or a chartplotter, the Sportbootführerschein alone is not enough to legally operate a radio: you need a separate, independent radio operator’s certificate, depending on your cruising area either the UBI for inland waterways or the SRC for coastal waters. How both certificates are structured, what they cost, and which one fits your cruising area is explained in detail in UBI or SRC – Which German Radio License Do You Need?.

Modern radios often include DSC (Digital Selective Calling), which lets you send an automatic distress call including your own GPS position at the press of a button. For DSC and AIS transponders to be clearly linked to a specific vessel, the boat needs its own MMSI number (Maritime Mobile Service Identity), which in Germany you apply for through the Bundesnetzagentur, the federal network agency. This number is tied to the boat and its radio equipment and should be in place before you first use a DSC-capable radio or an AIS transponder.

What This Means for the SBF Exam

Even though GPS, chartplotters, and AIS have long become everyday tools on modern boats, the navigation task in the SBF See exam still requires the classic approach: paper chart, course plotter (navigation triangle), and dividers. The reason is simple: once you’ve understood the logic of course, distance, and position by working through it by hand, you can transfer that knowledge effortlessly to any chartplotter, regardless of manufacturer, whereas the reverse path is considerably harder. That’s why it’s worth having the fundamentals from the articles on reading a nautical chart and compass variation and deviation firmly under control before you start leaning on the convenience of modern electronics.

In practice, classic and electronic navigation work best together when you use both in parallel, rather than relying exclusively on one method:

Plan your passage on the paper chart first, even if you’ll use the plotter underway. That way you keep the overall picture in mind and notice deviations faster.
Regularly cross-check your position on the paper chart, for example by taking bearings on known landmarks, instead of trusting the plotter display blindly.
Carry a backup power source and a backup device, such as a power bank or a simple handheld GPS, in case your fixed electronics fail.
Use AIS as additional information, but keep actively looking out, since not every boat transmits a signal.
Keep both chart software and paper charts up to date, so both sources show the same, corrected information.

Building these habits early lets you enjoy the convenience of modern technology without being left helpless if it fails.

Conclusion

GPS, chartplotters, AIS, and VHF radio have made navigation on the water noticeably more convenient and, in many situations, safer. But they don’t replace the fundamentals you learn for the SBF See: if you can reliably fix course, distance, and position using a chart and compass, you can use modern electronics as a genuinely useful addition while staying prepared for the moment the technology fails. Operating a radio also brings the matching radio operator’s certificate into play, which has to be obtained independently of the Sportbootführerschein.

The Boatpass app helps you build a solid grasp of the navigation fundamentals for the SBF See, with the complete official ELWIS question catalog and realistic exam simulation, so you always know where you stand, even without a chartplotter.