In this charcoal on paper drawing by Clifford Ashley, shipwrights seal the planks of a ship. Caulking was a process to make the joints in a wooden ship watertight. The caulker forces oakum between the planks using an iron and a caulking mallet. Then, pitch (pine tar) is poured along the seam to make a seal. Caulkers were among the highest paid tradesmen because their work kept the ship afloat.