The Lead Line

Ancient navigators developed a simple but ingenious manual sounding device, called the lead line, which is still in use today. A lead (pronounced ‘led’) line consists of a long rope with a weight at the end. Knots, or colorful markers, tied into the rope mark off every fathom, that is, every 6 feet or 1.8 meters. Navigators can estimate the water depth by counting the markers on the rope as the weight sinks to the bottom.