Collision avoidance: The eyes have it

Terry Slattery

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A safe day on the water includes avoiding collisions with all the other boats. Even away from popular boating areas, it’s important to have good situational awareness so you can act early to avoid a collision.

Eyeball it

Your eyes are your primary collision-avoidance aid. By keeping a good lookout, you can identify potential collision situations in plenty of time to act quickly and clearly to prevent a collision.

Your crew can help provide eyes in the back of your head by pointing out nearby vessels headed in your direction. Take the opportunity to educate them about boating safety, the rules of the road, and how everyone is responsible for avoiding collisions.


Electronic navigational aids like radar can help us in situations where our eyes may have problems.

To be safe, treat radar and AIS information as aids to navigation, not as definitive collision avoidance mechanisms.

Radar allows us to “see” through inclement weather and identify unlit obstacles in the dark. Radar comes in two types: traditional pulsed radar and newer broadband doppler radar. Each has advantages, which vary somewhat by vendor. In general, pulsed radar has greater range and better storm visibility while doppler radar has greater close-in resolution. Another recent innovation is the use of MARPA (Mini-Automatic Radar Plotting Aid) to identify and track targets.

It’s important to practice using radar during good conditions to learn how to identify and track targets. Watch some YouTube tutorials, and then apply what you’ve learned out on the water. Take the time to understand how you can identify fixed targets like buoys or anchored fishing boats as well as moving vessels.


Another aid growing in popularity is AIS (Automatic Identification System). This system broadcasts vessel information that can be used to identify and avoid collision scenarios. However, AIS isn’t prevalent enough to rely upon, so always back it up by keeping a good lookout.

AIS proponents point to the number of phone and tablet applications that show vessels anywhere around the world. These systems rely on ground stations or satellite receivers to pick up the vessel transmissions. However, I know of at least one situation in which a coverage dead zone put a sailboat into the path of a large ship in a narrow channel. The sailboat had relied on one of the marine AIS tracking apps. However, due to a lack of coverage, the large ship didn’t appear on the app.

Fortunately, the ship sounded its horn in time for the sailboat to change course and avoid a collision. In another situation, two big ferry vessels nearly collided when only one was transmitting AIS. And fishermen often turn off AIS so they don’t alert others to their favorite fishing spots. In summary, the absence of an AIS target doesn’t mean that there isn’t a vessel or other hazard at that location.

To be safe, treat radar and AIS information as aids to navigation, not as definitive collision avoidance mechanisms.

Finally, the best advice for collision avoidance is standard for navigation: Use multiple sources of information to avoid collisions. And don’t let electronics control your focus. You don’t want to run over a crab pot, run aground, or collide with something because you were concentrating on your electronic devices.

Terry Slattery

Terry Slattery has extensive sailing and ocean racing experience in a wide variety of boats. He has taken multiple trips on the AICW, in the Bahamas and the BVIs. His engineering background prompts him to enjoy projects, documented on his blog, that would normally be handled by a boat yard. He contributes monthly safety articles to the Annapolis Sail & Power Squadron/5 newsletter, Anchor Watch.

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