Historical information

The lead line or hand lead is a simple navigational instrument used as a depth finder to measure the depth of water under the ship’s keel and to take samples of the sea bed. The long line may be marked at regular intervals with tags of different coloured and textured fabric, such as rope, leather and cloth. Each tag was a code to represent a certain depth. The leadsman’s eyes and hands could distinguish the depth easily as he drew in the lead line, day or night and in poor weather conditions.

A standard set of codes for the tags was used so that the depth of the sea could be easily and quickly read. The measurement used was a Fathom, which equals 1.83 metres. The codes were: -
2 fathoms = 2 strips of leather
3 fathoms = 3 strips of leather
5 fathoms = white duck fabric
7 fathoms = red bunting fabric
10 fathoms = leather with a hole
13 fathoms = blue serge fabric
15 fathoms = white duck fabric
17 fathoms = red bunting
20 fathoms = 2 knots

The lead weight could be between 7 -14 pounds (3.5 – 6.5kg) and the rope would be approximately 25 fathoms (45m). The hollowed-out end of the weight would hold a stick substance such as tallow or wax, which would pick up samples from the sea bed which would show whether the vessel was close to, or far away from, the shore.

The leadsman would stand at the front of the vessel and cast the lead line into the sea. When it hit bottom he would note the tag marker nearest the surface of the water and call out his finding. Then he would haul it up again and examine the kind of matter that adhered to the end of the weight, whether it be sand, mud, gravel, or the colour of it. This information would be given to the ship’s helmsman or navigator and would help indicate the proximity to the land.

Significance

This handheld lead is an example of early marine navigational equipment used by sailors to travel the seas to measure the depth of the water and sample the nature of the seabed. It helps to understand the history and progress made from the very basic to the sophisticated technology of today.

Physical description

Lead line, sounding line or depth finder. The long length of rope has a heavy lead weight attached to the end. Coloured fabric tags are tied onto the rope at regular intervals, representing different depths. The concave base of weight holds sticky substances such as tallow or beeswax, providing an adhesive surface to collect samples of sea bed like sand, shells or pebbles.