CA-706 Copper-Nickel Alloy Hulls: The Copper Mariner's Experience and Economics
Actual four-year operating experience with the CA-706 copper-nickel alloy hull of the Copper Mariner has shown it to be a good business investment for workboats and potentially for large vessels as well. Capital recovery period is under seven years and return on investment between 12.9 and 16.7 percent after taxes for shrimp trawlers of this type. The resistance to biofouling is found to be a stable, enduring property of the same corrosion product film that gives the CA-706 alloy its very low 0.05-mpy (mills per year) corrosion rate. Both the corrosion resistance and biofouling resistance are unaffected by the amount of iron in solution or precipitated in the alloy, by the mill processing variables, or by shipyard fabrication. The CA-706 alloy hull demonstrated unusual resistance to crack propagation when subjected to unanticipated local high cyclic stress loadings. Construction, design changes, and damage repair procedures for steel are applicable to CA-706 alloy. The use of copper-nickel and copper-nickel clad hulls offers the marine industry an opportunity to operate vessels close to initial design efficiency for 30 years or more with no need to drydock for four or more years.