Measuring depth The lead

The lead is one of the oldest navigational instruments and was used to measure the depth of the sea. This measurement was essential when the ship passed shallow waters near reefs, approaching ports of destination or in unknown harbours.

It was usually made of lead and tied to a line, the lead line. Pieces of coloured cloth were tied at fixed intervals along the line, and thus the depth could be measured in feet or fathoms. To find out the type of sea bed, the lead was greased with tallow to which mud, sand or seaweed would stick.