A Vessel for Offshore Construction In Heavy Seas

Abstract Increased worldwide demand for oil is accelerating offshore exploration and production and is extending its boundaries to deeper and rougher waters. New technology and equipment is required for operation in these conditions, since the utilization of conventional equipment is diminished and its use, therefore, becomes uneconomical. In June, 1969 the world's first column stabilized construction barge was christened "CHOCTAW". CHOCTAW's construction followed an extensive design and development program which included three series of tank tests. During the past year, CHOCTAW was engaged in construction and pipelaying operationsin the Bass Strait, where she compiled an impressive record of performance in rough sea conditions. This paper discusses the engineering considerations which led to the CHOCTAW design and how they were realized. Actual motion and mooring forces data obtained on board the vessel is presented and compared with tank tests predictions. Based on the available preliminary data, the paper describes a method to predict CHOCTAW's motions in various sea conditions. While conventional construction barges will no doubt continue to develop oil fields in relatively calm waters, a new generation of column stabilized construction barges will operate in rough sea areas. CHOCTAW realized actual performance in seas exceeding 16 feet, and being the first such vessel, constitutes a unique departure from the conventional design. Foreword Increased worldwide demand for oil and oil products and political uncertainties in some of the major oil producing areas. are accelerating the search for oil offshore and extending its boundaries to deeper and rougher waters. Search for oil is currently being conducted in the Norwegian North Sea. the Grand Banks of Newfoundland. New Zealand's Cook Strait. Australia's Bass Strait. the Coast of Argentina and a number of rough sea areas off the African coast. The offshore drilling industry has developed a number of exploration vessels which can operate in these areas with minimum downtime. Once oil is discovered. its production necessitates the construction of platforms and production facilities. as well as underwater storage and pipelines. A great many construction barges were built to fill this need. Until June. 1969. all construction barges had conventional box shaped hulls. a feature which limited their operations to seas not exceeding five feet. Because of the excessive motion in high seas. these barges had to be towed a way to sheltered waters whenever a storm was forecast. In June, 1969, the construction barge CHOCTAW was christened. CHOCTAW was an important turning point in the industry in that she is the first column stabilized construction barge and is capable of sustaining operations in up to sixteen foot seas and maintaining her station in unrestricted oceans.