You'll find preferred channel markers where a channel splits in two or converges with another channel, or over an obstruction. You'll find dual-purpose aids in the Intracoastal Waterway between Texas and New Jersey at junctions with other bodies of water. You'll find special-purpose marks over or near temporary obstructions or hazards, such as fishing nets, dredging limits, anchorages, etc. You'll find range markers in busy commercial harbors. By positioning your boat so that the pattern or lights of two range markers line up, you’re is assured of being in the center of the channel.