Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.
Issue link: http://uscgproceedings.epubxp.com/i/264352
www.uscg.mil/proceedings 64 Proceedings Winter 2013–2014 into multipurpose supply vessels certifcated under subchapters D and O (tank ship) and subchapters I and L. Offshore supply vessels also serve as oil spill recovery vessels or as vessels of opportunity to apply oil dispersant chemicals or skim oil from the ocean. Current offshore drilling projects are moving far- ther from shore and into deeper water. This requires larger quantities of drilling mud, fuel, and drill pipe. This has resulted in OSV hulls approaching 300 feet, with larger and more numerous cargo tanks. Most operators view an offshore supply vessel hull as a temporary platform to build needed capability upon and then later change to meet new market demands, similar to a truck chassis that interchanges a box van with a cargo tank as needed. A notable example is the specialized OSV that conducts well stimulation or "fracturing" services for offshore facilities, which involves pumping chemical mixtures such as acids or aromatic hydrocarbons into a well to increase fow rates. As such, this type of offshore supply vessel lacks the large open cargo deck and instead will have multiple smaller-capacity integral and portable product tanks with multiple pumps and transfer piping systems. Some offshore supply vessels are also modifed to perform seis- mic survey work to assist locating commercially viable oil deposits. But even these more specialized OSVs have been converted to conventional multifunction offshore supply vessels when market demand changes. In a further design development, some OSV operators have investigated using LNG as fuel to reduce air emis- sions like carbon dioxide, nitrogen oxides, and sulfur dioxide. However, the logistical challenges of refueling at dockside, higher construction costs, and uncertain During the operation of an offshore facility, an offshore supply vessel delivers all of the consumables such as potable water, diesel fuel, groceries, and spare parts to a mobile offshore drilling unit (MODU), rig, foating off- shore installation, or fxed platform (also called offshore facilities). As a follow-on to the initial offshore supply vessel design, a very specialized type of OSV was developed called a liftboat. Rather than transporting routine cargo, these vessels primarily provide services to offshore facilities or transport heavy or large pieces of equipment. These self- elevating vessels force their legs into the seafoor until the liftboat is lifted out of the water. The liftboat can then serve as a stable platform for: • initial platform construction; • well maintenance, such as wireline work and pipe- line clearing; • structure maintenance, such as blasting and paint- ing; • end-of-life decommissioning and platform removals. Liftboats also began service as uninspected vessels, but moved to inspected vessels status by 1998. Current Design Trends The trend in OSV design incorporates greater capacity and capabilities, while keeping the multifunction charac- ter intact. This multifunction character is evident in some current offshore supply vessels that are dual certifcated to function as both an OSV (under subchapter L) or as a "cargo and miscellaneous vessel" (under subchapter I), when doing salvage work or other operations not related to offshore energy production. In the height of fexibility, one industry company recently converted two tank ships The 177-foot long, 3,915 GT liftboat Robert is a very large example of this special OSV class. Photo courtesy of Montco Offshore Inc. The 380-foot long multipurpose supply vessel HOS Centerline has its house in the aft part of the hull. Photo courtesy of Hornbeck Offshore Services. Winter �2013_45.indd 64 2/10/14 9:32 AM