Lead line

A means of finding the depth of water near coasts and probably the earliest device used by coastal navigators to facilitate safe navigation. It consists of a hemp line with a lead weight attached (about 7 pounds). A lump of tallow is pressed into a hollow at the base of the lead to bring up samples of the bottom: sand, mud, shingle, etc. The lead line is marked at specific intervals: 2, 3, 5, 7, 10, 13, 15, 17, and 20 fathoms. Different kinds of marks are used so the leadsman can tell the depth even in the dark.