Understanding Radar: A Vital Tool for Safe Sailing

As offshore sailors and professional marine technicians, we often emphasize the importance of integrating radar with your vessel’s navigation system as a means of safe seamanship.

Radar technology has made significant advancements in the past decade. Gone are the days of bulky, heavy, and power-hungry radar domes. The latest pulse compression radar systems are lightweight—typically under 5kg/11lbs—consume minimal power, and provide excellent resolution at both short and long ranges. But why should you have radar on your boat?

In simple terms, radar helps you "see" what's around your boat, even in darkness, rain, or poor visibility. Whether you’re navigating a busy shipping lane in thick fog, tracking squalls offshore in the tropics, or pinpointing a tricky harbor entrance at night, radar quickly becomes an invaluable tool for both navigation and safety.

How Radar Works

Radar, which stands for Radio Detection and Ranging, works by sending out radio waves from a transmitter. These waves travel through the air, hit objects, and bounce back to the radar’s receiver. The radar system then calculates the time it takes for the waves to return and uses this information to determine the distance to the object, its direction, and even its relative speed.

A radar display will typically show blips or arcs representing objects or terrain around your vessel. More advanced systems may use digital interfaces with detailed mapping and can integrate with other navigation equipment such as your chartplotter or MFD (Multifunction Display), and AIS (Automatic Identification System) for enhanced situational awareness. Surprisingly, this level of integration and networking has become remarkably affordable and achievable for many boaters. Most cruising boats fitted with a robust NMEA 2000 network can easily install and integrate a radar unit.

Benefits of Radar

1. Increased safety in low visibility  

One of the primary benefits of radar is its ability to provide a glimpse of what’s around you in all weather conditions. Unlike the human eye, radar can "see" through fog, heavy rain, and even darkness, allowing sailors to navigate safely when visibility is poor. This is especially vital in areas known for rapid weather changes or in regions where dense fog is common. In the Pacific Northwest, the month of August is often referred to as “Fogust” due to the thick fog that regularly blankets cruising grounds from Southeast Alaska south to the Salish Sea. Low-altitude stratus clouds that form when moist air from warmer waters moves over cooler waters, causing the air to cool and condense into fog.

2. Collision avoidance  

Radar helps you detect other vessels and obstacles in the water, even when they’re too far away to be seen with the naked eye or in blind spots where the horizon is obstructed from deck-level view. This feature is invaluable for avoiding collisions, especially in crowded or narrow waterways. AIS technology has also progressed by leaps and bounds in recent years, with many cruisers installing receivers (receive only) or transceivers (receives and transmits) on their vessels. And while this is excellent news for reducing collisions, it is not a foolproof solution. Military and fishing vessels are widely known not to consistently transmit their position, increasing your reliance on radar for detecting these vessels (which are usually much larger!) so that you are able to avoid them. Further, it is unwise to assume that all the boats you encounter during your travels will have AIS installed AND that it is operational. AIS + radar is a far more prudent collision avoidance strategy.

3. Terrain and navigation awareness 

Radar is an excellent tool for identifying landmasses, buoys, and other fixed obstacles, which of course is critical when navigating in coastal areas or when approaching harbors and ports. It provides real-time data on proximity, so you can adjust course early if necessary. It’s important to remember that ATONS (Aids To Navigation), especially buoys can move! Even from one cruising season to the next, they may not be located in exactly the same place as the last time you cruised that area, or the last time the chart was updated. In some cases moored ocean ATONs can have swing radiuses of over a mile!

4. Weather monitoring  

Radar systems can display weather patterns, such as rain, storms, and squalls, plus track their movement. This helps you to prepare for and oftentimes avoid potentially dangerous situations. For example, squalls and squall lines in the tropics are easily visible at night on radar. With the right display adjustments you can easily track their speed and direction of travel and make adjustments to your sail plan accordingly. Most cruising couples stand solo night watches, and having even just a few minutes of extra time before a squall arrives can make all the difference to your safety and comfort.

Limitations of Radar

As with all technology, despite its many advantages, radar is not without its limitations:

1. Resolution and clarity

Radar resolution can be affected by several factors. Smaller objects, such as buoys or fishing nets, may not be easily distinguishable, especially in old or poor-quality radar systems. Sometimes radar can confuse similar signals, like those from multiple vessels or landforms, leading to clutter or false targets on the screen. One of many reasons why even with the most advanced onboard systems it is vitally important to maintain a dedicated watch.

2. Range and accuracy

While radar can detect objects at long distances, the further an object is from the radar, the less precise the data will be. Especially offshore, where objects on the horizon may initially appear just as tiny blips. And, as you would come to expect, the accuracy of radar data is influenced by the ocean conditions. Waves, weather, and improperly installed systems that are not robust enough to handle anything but ideal ocean conditions can distort readings.

3. Power consumption and maintenance

Radar systems can be power-hungry, though this is quickly becoming less of a concern, even for sailboat cruisers with simple electrical systems and minimal power generation. Older models, however, can be extremely power-hungry, plus require regular maintenance and calibration. It’s essential to ensure that your radar is properly maintained and that you understand how to use it to maximize its performance. And good practice to investigate just how much power that old dinosaur you’ve got onboard might be sucking up. In many cases, our boat refit consultation clients find that if they’re already planning to install or upgrade to NMEA2000 devices, adding a new radar as well just makes too much sense.

4. False returns and interference

Radar signals can be affected by interference, such as from nearby ships and even your own boat’s electronics. While modern radar systems are equipped with filters to reduce this, it still requires periodic adjustments and vigilance to ensure that false returns don’t obscure critical targets. In practice, the proof is in the installation. DIYers, this is one area where it pays dividends for years if you invest in professional assistance during the system design and installation process.

Coastal vs Offshore Radar Applications

The way you use radar can vary greatly depending on whether you're operating in coastal or offshore environments. Both have unique challenges that radar can help mitigate.

In coastal navigation, radar is primarily used for avoiding collisions, particularly in busy shipping lanes, ports, or narrow passages. In these types of applications radar helps you keep track of multiple targets, such as nearby vessels, docks, and shorelines, even in limited visibility. The short-range capabilities of coastal radar systems are typically more focused on providing immediate situational awareness rather than long-distance tracking.

Offshore radar use is more focused on long-range detection and environmental monitoring. These systems may be optimized to perform best in open ocean conditions, where the radar’s ability to detect weather patterns and other vessels at great distances is crucial. Offshore radar allows you to detect vessels, icebergs, or other large objects up to several tens of miles away which affords you a longer response time. 

In some areas and seasons, storms can develop quickly and with little warning. This is becoming more rare in many areas due to advances in weather forecasting and modeling, but still holds true waters seldom navigated by commercial vessels and in the case of tropical squalls. In many cases you can monitor the size, direction of travel, speed of travel, and sometimes even intensity of squalls. Monitoring your radar allows you to anticipate changes in weather and take evasive action or prepare for a change in conditions.

Radar vs AIS?

AIS may seem like an easy-to-use and cost-effective alternative to radar, and it certainly touts an abundance of benefits. When networked with your MFD it allows you to see nearby vessels and navigational aids overlaid on your electronic chart, providing details such as the vessel's name, speed, heading, and more. You can even assess potential collision risks and contact the vessel directly via radio using AIS data. However, it’s important to remember that AIS only displays vessels that are actively transmitting. It will not detect objects without AIS transmitters, and depending on the vessel's speed, the data could be delayed by up to 3 minutes (sometimes more), especially at lower speeds.

By combining AIS with radar, you can enjoy the best of both worlds. AIS helps you identify and confirm vessels that are transmitting, and radar ensures you can detect targets that may not be broadcasting on AIS.

Conclusion

Radar is an essential tool for sailors of all experience levels. Its unique ability to improve situational awareness in conditions where human vision is unmatched. While it is not perfect, understanding how radar works, its benefits, and its practical limitations can make a significant difference in ensuring your safety at sea. By investing time in learning how to properly use and maintain radar systems, you’ll be better equipped to navigate with confidence—whether you’re cruising along the coast or venturing far offshore.

Don’t forget that your best safety measure by far is a well-trained, attentive crew who practice safe, conservative seamanship. Take the time to learn how your radar system functions. Push its buttons and turn its dials. See what happens. Experiment in familiar areas to give you a better idea of its strengths and weaknesses.