Lead Line

A marked line with a weighted lead used to measure water depth and, in some forms, obtain a seabed sample.

The line carries distance marks that are read when the lead reaches the bottom and the line is approximately vertical. A hollow or tallowed recess in the lead can bring up material indicating whether the bottom is mud, sand, shell or another substrate.

Vessel movement, current, line angle, stretch and wave motion introduce error, especially in deeper water. A lead line remains useful as an independent shallow-water check, but it samples only one point and must be deployed clear of propellers, people and snag hazards.