A Vessel for Offshore Construction In Heavy Seas
- Yoram Goren (Santa Fe International Corp.) | Bruce McMillan (Santa Fe Pomeroy, Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 1973
- Document Type
- Journal Paper
- 387 - 394
- 1973. Society of Petroleum Engineers
- 4.5.4 Mooring Systems, 4.2 Pipelines, Flowlines and Risers, 6.1.5 Human Resources, Competence and Training
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A new generation of construction equipment an evolving for offshore work in heavy seas. The progenitor of the line is Choctaw, the world's first column-stabilized construction barge. She is capable of sustaining operations in seas up to 16 feet and of maintaining her station in unrestricted oceans.
Increased worldwide demand for oil and oil products, together with political uncertainties in some of the major oil producing areas, is accelerating the search for oil offshore and extending its boundaries to deeper and rougher waters.
Offshore oil production necessitates the construction of platforms and production facilities, as well as underwater storage and pipelines. A great many construction barges have been built to fill this need. Until June, 1969, all construction barges had conventional box-shaped hulls, a feature that limited their operations to seas not exceeding 5 ft. Because of the excessive motion in high seas, these barges had to be towed away to sheltered waters whenever a storm was forecast.
In June, 1969, the construction barge Choctaw was christened. Choctaw represented an important turning point in the industry in that she is the first column-stabilized construction barge and is capable of sustaining operations in seas up to 16 ft and maintaining her station in unrestricted oceans.
Description of the Vessel
Choctaw Principal Dimensions
Length, ft 400 Beam, ft 106 Depth, ft 54.5 Low draft, nominal, ft 15 High draft, nominal, ft 29 Low-draft displacement, tons 14,049 High-draft displacement, tons 21,843 Light ship displacement, tons 10,429
The design principles used in the vessel are discussed in detail in Ref. 2. To restate the basic design philosophy, the designers recognized that a construction barge is seldom called upon to use her maximum crane capacity. For this reason, Choctaw was designed to operate in two different drafts. In the low draft, the crane can handle up to 800 tons at 90-ft outreach, and in the high draft, the crane can handle 150 tons at 110 ft with full deck load and no ballast compensation.
On several occasions the vessel was called upon to perform lifts heavier than 150 tons while in the high-draft condition. These exercises were carried out by maintaining the list angle to a minimum through transfer of ballast. Lifts of this type necessitate that careful planning and exacting calculations be carried out by the barge engineers.
The crane was designed to sustain a dynamic load produced by roll motion of 5 degrees in 9 seconds double produced by roll motion of 5 degrees in 9 seconds double amplitude (for all but the 800-ton load condition). The force produced by a 50-knot wind was superimposed on the dynamic loading. The crane was designed to sustain a 3 degrees barge list when lifting 800 tons.
The vessel was designed to operate in adverse climates: in temperatures ranging from -35 degrees to + 120 degrees F. Both design and construction were closely monitored and approved by Lloyd's Register and the U.S. Coast Guard.
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