The commercial maritime industry began advertising on Zippos in the 1940's. Until that time, the U.S. Navy was the principal sponsor of ship and marine themes to be engraved on the Zippo. A lot fewer Zippos with civilian ships and vessels such at paddle wheel boats, tugboats, freighters, ferries etc. have been produced than with Navy ships, making them rarer and more difficult to find by the Zippo collector. Among the lighters depicted below are two rare genuine scrimshaw Zippos. Scrimshaw is the art of carving designs on whalebone or whale ivory. Scrimshaw Zippos were test marketed in 1976-77 in three designs: the Outrigger, the Schooner, and the Whaler. Zippo found that "genuine" scrimshaw was too expensive for the average customer and in 1982 introduced scrimshaw designs on cases made of acrylic materials rather than ivory. These remain popular today, with a variety of attractive maritime-related designs featuring lighthouses and sailing ships.