buoy

buoy (boi, b`ē), float anchored in navigable waters to mark channels and indicate dangers to navigation (isolated rocks, mine fields, cables, and the like). The shape, color, number, and marking of the buoy are all significant, but unfortunately there are two competing systems of color coding which have been adopted in different parts of the world. The International Association of Lighthouse Authorities (IALA) adopted a system in 1977 which uses red for the left–hand side of a channel returning from the sea and green for the right side. Because the American rule has always been "red to the right returning," the IALA accepted a second system in 1983 which would keep the traditional color–coding for U.S. waters. Both systems use yellow to indicate special zones, such as fishing areas, anchorages, dredging operations, etc. Although the spar buoys (upright posts) used in northern latitudes are usually wooden, large buoys are generally made of steel or iron. Nun buoys have conical tops; can buoys have flat tops. Buoys may be fitted with bells or whistles (usually operated by motion of the waves), and battery-powered light buoys are commonly used; radio buoys came into use in 1939. There are also mooring buoys, used for the anchoring of ships.