Why Onboard Electronics Shouldn't Make You Forget the Basics of Seamanship
At a time when our chart tables are dominated by touchscreens, navigation apps, and satellite weather routing, sailing has never felt so effortless. However, this wealth of technology creates a sense of security that can often be misleading. Whether you are blue-water cruising or coastal sailing, onboard electronics are a tool to assist you, not an absolute guarantee. What are the true limitations of your plotters and apps? How do you prepare for a total power failure or GPS jamming offshore?
Navily takes a closer look at the issue. Drawing on the expertise of Mathieu André (Head of Cruising at Les Glénans), discover our analysis and practical advice for sailing with peace of mind, ensuring you always stay in control, even when the screens go dark.
The Limits of Electronics in Offshore Navigation
The screen of a chartplotter, tablet, or laptop instantly displays a vessel’s position on a clean, sharp graphic interface. A symbol of modern sailing, satellite positioning gives an impression of infallibility. But this is an illusion. This visually appealing digital rendering is an imperfect representation of reality. It must always be cross-checked by consulting nautical pilots, comparing data from other onboard instruments, and, crucially, keeping a sharp visual lookout. In short, it is by thoroughly understanding the limits of your onboard electronics that you can truly get the most out of them. Mathieu André, Head of Cruising at the Les Glénans base in Concarneau, explains how.
- Which Type of Electronic Chart Should You Choose?
- How Much Trust Can You Put in Digital Charts?
- How to Better Prepare for Electronic Navigation?
- The Core Work of a Navigator: Weather Analysis and Route Optimization
- Understanding Power Dependency
- The Vulnerability of Satellite Positioning
- Conclusion: Finding the Right Balance Between Tech and Seamanship
Which Type of Electronic Chart Should You Choose?
First came raster charts, which are exact digital scans of official paper charts. They replicate the layout, colors, and symbols perfectly. While the data they present is reliable, it is static; you cannot add new layers or set up automatic alarms if your route heads toward a shoal. Because they require significant storage capacity, they have largely been superseded by vector charts.
Vector charts are essentially a visual rendering of a database. When paired with navigation software, the displayed information can be customized, filtered, and enhanced with specific details on features like lights and buoys. They require less memory than raster charts, are highly adaptable, and scale smoothly to any screen size without losing legibility. Currently, only vector charts meeting the S-57 standard comply with official Electronic Navigational Chart (ENC) regulations. These are the ones to look for.
How Much Trust Can You Put in Digital Charts?
While major hazards are perfectly visible on a paper or raster chart even at a wide scale, they can easily be filtered out or hidden on a vector chart. “Certain software and digital chart combinations do not display navigational hazards at lower zoom levels,” warns Mathieu André. “When planning a coastal or offshore passage, it is vital to zoom in extensively along your entire route to spot any potential shoals.” Speaking of zooming on vector charts, beware of overzooming (zooming past the chart’s native scale). On-screen, your boat might look perfectly clear of danger, but you lose sight of the bigger picture, which can lead to nasty surprises in the real world.
How to Better Prepare for Electronic Navigation?
“The skills required for navigation aren’t tied to a specific medium; they are tied to a methodology,” notes Mathieu André. “This method consists first of passage planning, and then maintaining a continuous log, whether on a paper chart or with digital tools.” Once your route is plotted, you must zoom in on the electronic chart to check for hazards or consult detailed paper charts, “at least for the departure and landfall phases.” This cross-check should always be backed up by consulting a pilot book, almanac, or sailing directions. Ultimately, whether paper or digital, the charts you use must be up to date.
Unlike paper charts, updates for vector charts generally require a paid subscription after the first year. If your digital portfolio is too old, you will eventually have to purchase a new edition. To perfect your planning, remember that Urgent Notices to Mariners (AVURNAV), which announce critical safety changes, are accessible on PING, the international nautical information platform. They can also be downloaded for free to be integrated directly into your navigation apps.
The Core Work of a Navigator: Weather Analysis and Route Optimization
“Sailing today means you can almost entirely avoid running into dangerous weather systems, thanks to the quality of modern forecasting,” says Mathieu André. The minimum baseline practice is to fetch the weather bulletin daily and monitor trends online. Offshore, out of cellular range, the boat must have at least one reliable method for receiving bulletins, such as a shortwave receiver or a Navtex unit. Even better, a satellite connection allows you to regularly download GRIB files to view inside routing software. According to Mathieu André, offshore navigation is fundamentally about managing and updating information. “Once my passage is planned, I can view my intended route on a tablet. I know exactly where I am going, my personal notes are visible, and having all the telemetry (wind, speed, heading) consolidated on a single screen is incredibly practical,” he explains. “It allows us to spend more time on deck, directly managing sail trim and optimizing our course.”
Understanding Power Dependency
Instruments like wind transducers, radar, depth sounders, satellite antennas, speedos, AIS, and autopilots can all be networked (most commonly via NMEA 2000) and accessed via Wi-Fi throughout the boat. This setup is the gold standard for fine-tuning sail trim and making helm management effortless. However, it also makes the skipper entirely dependent on a reliable power supply. Onboard electronics consume significant power, requiring strict battery management and a disciplined charging routine. As a precaution, captains must anticipate a total blackout by keeping a few paper charts and a backup handheld GPS with enough battery life to make landfall.
The Vulnerability of Satellite Positioning
After power dependency, the other major vulnerability for modern sailors is our reliance on satellite positioning. The first network, GPS (Global Positioning System), was launched by the US Department of Defense in 1978. Its free civilian signal remains subject to military discretion, just like the Russian GLONASS or Chinese BeiDou systems that followed. GPS jamming in conflict zones has been thoroughly documented for decades, notably in Iraq and Afghanistan. The European Galileo network is currently the only global satellite navigation system under civilian control. With a nearly complete constellation, it is fully operational and compatible with most modern smartphones and plotters. It is also used in modern EPIRBs (Emergency Position Indicating Radio Beacons).
However, like all components of the Global Navigation Satellite System (GNSS), Galileo’s signal can still be disrupted by jamming or spoofing, as evidenced by recent disruptions in the Baltic Sea, the Eastern Mediterranean, and near Ukraine following the 2022 invasion. Even though these hybrid warfare tactics are localized, skippers need to “know how to navigate in degraded modes,” as Mathieu André puts it, and have a backup plan ready. Close to shore, this means relying on the classic quintet: a hand-bearing compass, a plotter/parallel ruler, dividers, a pencil, and a paper chart. Offshore, without a sextant, you must rely on dead reckoning from your last known position until you make landfall.
Text by Laurent Charpentier / [email protected]
Conclusion: Finding the Right Balance Between Tech and Seamanship
Marine electronics and navigation apps have revolutionized the way we travel at sea. They reduce a skipper’s cognitive load, allowing for more time on deck in harmony with the elements. However, as we have seen, traditional seamanship and proactive passage planning (system redundancy, updated charts, power management) remain your best allies when things go wrong.
At Navily, we firmly believe that technology should serve your freedom, never replace your vigilance. Whether you are preparing for a transatlantic crossing or a simple coastal cruise, the key lies in cross-checking your sources: your digital tools for precision, your eyes for reality, and the feedback from our community for practical, real-world experience. Wish you fair winds and safe sailing!
Les Glénans is a non-profit association recognized for public utility and approved by the French Ministry of Sports. Founded in 1947 in the Glénan archipelago in Brittany, the school is now the largest in Europe and the gold standard for sailing instruction.
Since its inception, the association has grown continuously while remaining true to its founding values: volunteering, community living, solidarity, and self-reliance. Every year, it runs nearly 4,000 courses, bringing together over 19,000 students and instructors.
As a major force in the development of leisure boating, Les Glénans has expanded far beyond its Breton roots. From Paimpol to Bonifacio and across the West Indies, the association has been passing down its expertise to generations of sailors for nearly 80 years. Its teaching model has helped shape legendary sailors, including the likes of Vincent Riou and Franck Cammas.
