Screwpiles: The Forgotten Lighthouses

Hydrographic Surveys – Lead Lines to Sidescan Sonar Sailors have always needed to know the depth of their water

and what was on the bottom. For centuries, the lead line was used, a simple method using a weighted line dropped overboard, the depth measurement taken when the lead hit bottom. Various weight designs were used to capture bottom samples so that the mariner would have an idea of what was below. Machines were eventually developed, making the process faster and more reliable. The method was tedious and yielded only a single point of information for each sounding. In the early 1900s, Nicholas Heck of the U.S. Coast and Geodetic Survey improved a wire dragging

Sounding apparatus, 1877 Wikipedia

technique, advancing hydrographic survey operations. His method used two vessels to drag a wire at a set depth. When an obstruction was encountered, the wire formed a “V,” indicating its position. The technique allowed for accurate and more rapid mapping over a wide area, and it was used extensively into the 1990s. 15

U.S. Coast & Geodetic Survey

Sidescan sonar and multi beam swath systems made the wire dragging system obsolete. With this technology, surveys could be taken over a wide area to any depth by a single vessel. The speed and accuracy of this system allowed for more detailed charts with more frequent updates.

U.S. Coast & Geodetic Survey

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