Heaving the lead

As soon as a vessel came near land her crew would begin “sounding” the depth of water using a line marked with depths and a length of lead. The word sounding is dervived from the old English sund (for water) and the depths found could be related to depths marked on the chart to give an idea of position (especially if you had at least one position line). The lead was hollow on hte bottom and this was filled with tallow (called arming the lead). The sticky tallow would pick up a sample of what was in the sea bed and this could also be cross referenced to the chart. Sounds were a vital part of navigation in thick weather and were constantly taken whenever the ship was in fog.

The leadsman stood in the fore channels (or by the shrouds on smaller vessels) and swung the lead to drop it ahead so that it sunk to the bottom matching the ship’s speed. Sometimes the lead was dropped at the bow and the line was kept aft where the mate would be waiting with the line tub, to read the depth on the line which had hopefully hit the bottom by then.

The leadsman called: “All ready there?” and the mate shouted: “Heave!” The lead went arcing forward taking the line out of the leadsman’s hands or sometimes out of the tub. Other hands were positioned between the leadsman and the mate letting the line run out taut as it went aft. When the lead hit the bottom the line went slack and the nearest man made the sounding, and called the mark.

Marks were made in fathoms, or six feet (1.83m) lengths. And this was the length represented by the leadsman’s outstretched arms as he counted in the fathoms of the leadline. The name derives from Norse fathmr and Old English faedm or faethm, meaning outstretched arms.

Various marks on the line, of leather, calico, serge and bunting indicated the depth in fathoms and could be felt and identified in the dark. The lead was then retrieved. A hollow in its base would have been “armed” with a plug of tallow – which picked up a sample of the bottom; mud, sand or shell, which further helped identify the ship’s position. DMH

Lead lines are normally 20 fathoms in length, though 15 or ten would do for most small yachts if they are using the line as an aid to an electronic depth sounder. A lead line is still useful for calibrating the depth sounder and can be taken off in a dinghy to “sound out” an anchorage say. There are traditional ways of marking a lead line but marks in metres are a good idea to reflect your charts (unless you are using fathoms), and a simple system of knots or marks will work. Plastimo for instance make a 30m lead line with every metre marked by a colour toggle, with the colour changing every ten metres.

Traditional lines are marked thus: