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Gear Test: LIGHTrule and ROADrule

Weems and Plath of Annapolis, Md., recently introduced two products that should be a welcome additon to anyone's navigation tool kit.

Weems & Plath of Annapolis, Md., has been in business since 1928 and produces a variety of precision marine instruments for pleasure boaters, cruisers, yacht racers commercial mariners and the military. The company recently introduced two products that should be a welcome addition to anyone’s navigation tool kit.


The LIGHTrule and ROADrule are simple-to-use identification tools that provide pictorial references for USATONS (U.S. aids to navigation) and COLREGS (Collision Avoidance Regulations — lighting configurations as defined in the Inland Waterway Rules of the Road) as well as several other areas of importance to anyone operating a boat on U.S. waters.

Knowledge of the information provided by the LIGHTrule and ROADrule is critical to the safe operation any vessel. Of course, this information is readily available from numerous other sources, but until the introduction of these weatherproof slide rule-style devices, locating it usually meant flipping through pages of a book or viewing already cluttered charts. This usually means we can’t conveniently find the information that we need, when we need it.

The LIGHTrule and ROADrule are identical in form, function and assembled quality. They are flat and constructed mainly of black PVC, with stainless steel rollers and clear Lexan viewing bars that magnify the definitions. They work like an old-fashioned slide rule, with the center section sliding through the outer sleeve. The center section measures 16 inches long and slides within the main 9-inch sleeve. The sliding section incorporates detents that ride against the stainless steel fasteners on each corner, keeping the selected viewing windows aligned.

The ROADrule identifies the most common aids to navigation by allowing the user to slide the center section of the tool to the left or right until the navigation aid or marker is displayed in the viewing window, with the corresponding chart symbol displayed in the window directly above. I found the chart symbols and navigation aids clearly and accurately illustrated.

After aligning the correct illustration in the window, rotate the tool a quarter turn and read the definition through the magnifier. For example, “Lighted Buoy — PREFFERRED CHANNEL TO STARBOARD — May be Lettered — Green Light Only.” Also on that side of the tool is information regarding bridge lighting configurations, buoy and beacon light descriptions (i.e., Fl G 6 sec) and Intracoastal Waterway markings. On the other side of the ROADrule are maneuvering and warning (sound) signals, along with the sliding selector window depicting which vessel is the give-way (shown in yellow) or stand-on. It also includes diagrams for sailing vessels operating under various wind directions and tacks.

The LIGHTrule operates in the same manner but shows 60 different lighting and day shape configurations. One side of the tool shows the lights as viewed bow-on or port side, with “Sound Signals in Restricted Visibility” printed on the sleeve, while the other side shows stern and starboard side views, with standard maneuvering and warning signals on the sleeve. The lighting configurations are printed in representative colors of white, lime green and red. Both the green and white are readily visible under reduced lighting conditions, though the red is more difficult to see and is almost impossible under red cockpit lighting at night.

I found both tools intuitive to use. They are stored in their own vinyl sleeve with instructions printed on one side. The ROADrule instructions are clear, accurate and easy to follow, but I did stumble with the LIGHTrule instructions. The tool is simple to use, but several people I handed the package to were confused by the printed directions.

Although I’ll keep the ROADrule and LIGHTrule at the helm station to serve as memory aids, I don’t consider them replacements for good, working knowledge of aids to navigation and COLREGS. They are excellent reference and study tools at home, as well. They can turn the occasionally tedious work of reviewing the material into an agreeable event.

Weems & Plath also offers a ROADrule for European inland waterways and international waterways, as well as a LIGHTrule for European waterways. Retail price is $24.99 each, and they are available on the Weems & Plath Web site ( ) and through most marine retailers that carry navigation tools.