1 A small platform on either side of a ship from which the leadsman took soundings to ascertain the depth of water. They were so called because originally, in the early days of sail, the leadsman cast his lead standing between the shrouds, which were attached to the chain-plates or, earlier still, to lengths of chain attached to the ship's side. The name was retained, and was still apposite while soundings were taken in this way, as a small chain was later threaded through stanchions at waist height rigged round the platform to prevent the leadsman from falling overboard as he made a cast. See also lead line.
2 The wooden projections from the sides of square-rigged ships, abreast each mast, which carry the chain-plates clear of the gunwale capping to prevent chafe, and to give the shrouds a wider base and spread from which to support the masts. They are secured to the ship's side by knees and bolts, each mast having its pair, one on each side of the ship. The name originated from the lengths of chain which preceded chain-plates as the fitting to which the deadeyes of shrouds were secured. They are also known as chain-wales (spelt and pronounced channels in the US Navy).