Bottom fouling. It's a problem as old as boats. The Phoenicians and Greeks smeared hulls with pitch mixed with wax or tar and applied it hot. Or they mixed arsenic and sulfur with tar in hot oil and burned it into the hull with an iron — a method the ancients called "ship painting"
“Marine Fouling and Its Prevention,” a 1952 report that Woods Hole Oceanographic Institution prepared for the Navy, sheds light on these and other methods in the history of antifouling coverings and coatings.
The Romans used lead sheets fastened with copper nails over a corrosion-preventing layer of paper or cloth. While that process did keep ship worms at bay, seaweed still fouled the bottom; even still, the method remained popular well into the Middle Ages. (Leonardo da Vinci helped by inventing a machine for making sheet lead.)
Christopher Columbus preferred the antifouling qualities of a coating. His ship bottoms were “painted” with tallow and pitch. Fellow explorer Vasco da Gama charred his hulls to a depth of “several inches.”
Antifouling “paints” emerged in the 17th century. They were noxious mixtures: powdered iron, cement and a copper compound; glass mixed with tar, oil and lime; molten tin in a paste of zinc, limewater, black soap and salts of zinc; arsenic, iron sulfide and zinc mixed with varnish. They did not have a good reputation.
Then came copper sheathing. The 18th century cure-all worked as a protection against worms and didn’t foul. The USS Constitution, “Old Ironsides,” was copper-clad.
The 19th century iron hull changed all that. At first, the copper sheathing was insulated from the iron hull with a layer of felt soaked in tar; it didn’t work, and the demand for a non-corrosive, antifouling coating increased. The 20th century provided it. In 1908, the Navy approved a coating using red mercuric oxide in gum shellac, grain alcohol, turpentine and pine tar oil. Zinc oxide, zinc dust and “Indian red” were further additives.
It and other 20th century coatings, the report states, “led to the development of the modern paint systems.” (For the record, the advertisement here is from a 1959 issue of Motor Boating magazine.)
This article originally appeared in the November 2017 issue.