Use of the Massachusetts Dip Oil Skimmer on Free Slicks in the Casco Bay (Portland) Spill

Abstract

ABSTRACT On July 22, 1972, the tanker Tamano, carrying a full load of No. 6 fuel oil, sustained a ruptured tank and reportedly spilled on the order of 100,000 gallons of oil in Casco Bay. For two weeks following the accident, the Tamano was anchored and surrounded by containment booms while its cargo was off-loaded and cleanup operations were performed. This paper describes the role that the Commonwealth of Massachusetts' newly developed Dynamic Inclined Plane (DIP) Skimmer played in the cleanup operation and presents observations and evidence of the need for, and effectiveness of, a mobile skimmer in large spill situations. The paper also discusses the necessity of testing an operating plan especially as it relates to the cleanup hardware to be used. The feasibility of skimming free slicks is discussed in the paper and demonstrated in a film. The role of support vessels in maintaining the skimming operation and handling the collected liquids and solids is examined. The effective use of skimmers is demonstrated over a wide range of environmental conditions and the full range of oil debris conditions from the newly spilled, relatively clean oil to the weathered straw-seaweed-debris-laden material that exists after several days. The oil skimmer was secured to the side of several different vessels and used in a sweeping mode to collect heavy, weathered No. 6 oil, oily straw, oily seaweed, and debris. Several conditions are presented including harvesting of windrows of oil and debris, harvesting thick oil in a free slick (in seas several feet high), and harvesting both thick oil and sheen leaking from a boom. The effectiveness of these operations is explored in terms of both pickup and transfer. There are a number of important observations and conclusions to be gained from this experience and from the experiences of other large spills. Skimming operations can be effective, not only at the outset of a spill, but also during all phases of the cleanup operation. Development work is needed if skimmers are to handle the large volumes of solids as well as oil present. Skimming of free slicks, and leaks from boomed areas, is not only effective, but necessary, to reduce the environmental and economic impact of the spill. There is an urgent need to provide mobile storage to handle the high volumes of heavy oil and debris which can be recovered by second-generation skimmers.