Oil Spill Risks From Tank Vessel Lightering (1998) / Chapter Skim
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3 Lightering Vessels, Systems, and the External Environment
3 Lightering Vessels, Systems, and the External Environment
Pages 50-68
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From page 50... ...
Cargo owners commonly contract with independent lightering service companies to provide equipment and supervisory services during lightering operations. These service companies may also operate the service vessels that shuttle cargo to refineries, or they may perform their services using chartered or independently operated vessels.
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From page 51... ...
The committee identified these systems based on its members' backgrounds and expertise in lightering as well as on a review of the literature and information gathered from industry, regulators, and others during the study.3 The key elements of vessels and special systems are vessel design, mooring systems, rendering systems, and hoses and transfer systems.4 The key elements iCompanies that have in-house guidelines and standards include Chevron Shipping Company, Skaugen PetroTrans, Maritrans, SeaRiver Maritime, Conoco, Statoil, and Shell Oil Company. 2For a more detailed discussion of navigation aids and electronic traffic systems, see NRC 1994a, 1996.
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From page 52... ...
Mooring lines, fenders, and hoses are usually delivered to these vessels just before a lightering operation, used during the offloading of one STBL, and then removed by the service company that was engaged to provide this equipment, expertise, and personnel for the lightering operation. These nondedicated vessels are of varying designs, so the special equipment must be able to accommodate a variety of on-board arrangements.
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From page 53... ...
recommended that the USCG implement operational procedures and crew training for existing tankers that are subject to problems with intact stability and develop design requirements to ensure the intact stability of new double-hull tankers. Although the IMO and USCG efforts to address this problem appear to be adequate for shipping in general, lightering safety in particular will require that vessel operators and crews adhere strictly to the new guidelines and standards.
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From page 54... ...
However, committee members who have visited lightering operations and those who are experienced with lightering have pointed out that high freeboard is a problem worthy of attention. Preventive measures, such as ballasting, are straightforward and could lead to a safer operation.
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From page 55... ...
Single-hull vessels that engage in lightering must also carry on-board equipment for emergency lightering transfer connections. The required equipment includes reducers, adapters, bolts, washers, nuts, and gaskets for at least two simultaneous transfer connections from the vessel's cargo manifold to cargo hoses ~ · .
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From page 56... ...
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From page 57... ...
Many companies have also established their own standards. Vessels moored together in an open seaway tend to move independently, and the motion can cause chafing and shock loads and the subsequent failure of mooring lines, particularly lines made of synthetic materials.
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From page 58... ...
Service vessel STBL FIGURE 3-1 Recommended mooring arrangements for offshore lightering. must be suspended and the vessels separated.
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From page 59... ...
59 mooring master or lightering service company representative tests the pressure of pneumatic fenders, which must be inflated according to the manufacturer's instructions (foam-filled fenders are sometimes used instead)
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From page 60... ...
60 OIL SPILL RISKS FROM TANK VESSEL LIGHTERING Fenders are deployed between the STBL and the service vessel. Primary fenders, which absorb the impact from the connection of the two vessels, must have the proper diameter in relation to the vessel's freeboard to prevent the fenders from riding up the sides of the vessel and rolling onto the deck.
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From page 61... ...
The guidelines specify numbers, types, sizes, and other criteria for fenders for particular operations and given conditions, such as vessel sizes and speed of approach. However, each operator should design a rendering system that suits the conditions of a particular lightering operation using the equipment performance data provided by the manufacturer.
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From page 62... ...
The industry guidelines for the construction and testing of hoses, together with the USCG regulations, provide high standards for the operations, testing, and inspection of hoses. Committee members who routinely conduct lightering operations noted that hose failures during testing are often caused by the separation of the internal liner.
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From page 63... ...
The National Data Buoy Centers operates offshore weather stations, funded by NOAA, that provide data to mariners by marine-band radio. Information from weather buoys and other sources is compiled by NOAA for weather updates broadcast by radio.
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From page 64... ...
, the wind direction and speed indicator were inoperable for most of 1997. There appear to be a number of ways in which weather forecasting could be improved to support lightering operations.
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From page 65... ...
These designations would assure mariners that specific areas are, and will continue to be, free of underwater obstructions and, therefore, provide safe anchorages. Designated Lightering Zones and Prohibited Zones To regulate certain lightering activities in the U.S.
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From page 66... ...
The committee recognizes that establishing lightering zones offshore would have both positive and negative effects on safety. On the positive side, the USCG could set safety standards with enforceable regulations and could prevent operators with questionable standards from engaging in lightering.
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From page 67... ...
First, lightering operations are safer when vessels have long parallel mid-bodies, an adequate number of well placed mounting points for fenders and enclosed chocks for mooring lines, and engines that enable controlled slow-speed operations. Second, all operators should use mooring lines with synthetic tails to absorb shock, adhere to appropriate standards when inspecting and testing hoses, and remain vigilant during their use.
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From page 68... ...
At present, the number of designated lightering zones or prohibited zones seems to be adequate, but one aspect of the current regulations could be improved. COTPs should have the authority to grant waivers allowing vessels engaged in lightering to depart from designated lightering zones when it would be safer than maneuvering or separating the vessels.
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