Aids to Navigation: Range Markers

In addition to dayboards and buoys, there are a few other aids to navigation to help mariners along their way. One example is a “Range”, also referred to as “Range Marks”, “Range Markers” or “Range Lights.”  A range is a pair of large rectangular dayboards, one higher than the other, that when aligned vertically, guide vessels through a navigable channel.

Range dayboards are mounted on structures, usually pilings, at two different heights.  From the navigable portion of the waterway, one of the dayboards is observed above and behind the other.  When you observe the rear dayboard directly above the one in front, you are in the navigable channel.  Each dayboard is painted with vertical stripes of contrasting colors for maximum visibility.

Ranges generally, but not always, mark the center of a channel.  On navigation charts, range markers are connected with a dash line in the non-navigable area, from which a solid line continues into the navigable channel.  The solid portion of the line indicates exactly where the range will keep you in the waterway.  When following a range, if the dayboards are not aligned, simply steer toward the lower one for course correction.

Almost all ranges are lighted. Your chart will indicate the color of the lights and their characteristic (flashing, fixed, etc.).  Unlighted ranges are usually in small waterways and are privately maintained.

Ranges are important both while approaching or traveling away from them.  They guide you in either direction.  However, watch out for a head-on collision possibility, since both you and the oncoming traffic may be on reciprocal courses.

We are reminded of an actual incident that occurred in the channel to a major Atlantic seaport.  We’ll change the names to “protect the innocent.”  Three sailors were heading for port aboard the sailing vessel “Confusion” when they approached what appeared to be a range.  They observed two white lights, one above the other, and kept them aligned.  They observed a red light to the right and a green light to the left of the range.  After four days at sea, they felt sure that the red and green lights marked the long awaited channel.

It was 1:00 a.m. and raining.  The silence was broken by a booming voice on VHF channel 16.  “This is the container ship “Gigantic” calling the vessel dead ahead of me.”  As Moe gave his shipmates Larry & Curly a terrified look, the voice continued, “Please alter your course immediately.”

The crew of “Confusion” quickly learned that what they thought was a range was the fore & aft masthead lights of an 800 foot ship.  What looked like red and green channel lights were actually the ship’s port & starboard sidelights.  After a frantic scramble for the helm, the crew of “Confusion” barely avoided disaster.  This incident gives new meaning to the saying, “That light at the end of the tunnel turned out to be an oncoming train!”

Had the crew of “Confusion” looked at their chart, the “imagined” range would not be found.  Also, they should have known that red and green channel markers have flashing lights, while a vessel’s red and green sidelights do not flash.  They won’t make that mistake again!

Until next time, we wish you clear skies, fair winds and calm seas!


World Wide Marine Training, LLC, is a U.S. Coast Guard Approved facility authorized to give examinations for captain’s licenses up to Master 200 Tons, Able Seaman up to Unlimited, STCW Basic Training, Radar, ARPA and other Endorsements. Please visit or call toll-free 866-249-2135.