New Class Rules for OSVs

Wednesday, August 12, 2009

The current status of new class rules and complementary solutions for safer operation of offshore service vessels (OSVs) were presented by Germanischer Lloyd's Helge Rathje at the 3rd International Conference on Technology & Operation of Offshore Support Vessels in Singapore. "Our aim is to formulate a set of new rules that are comprehensive, strict and feasible enough to help construct safer and more robust OSVs and to minimize their operational risks," he said.
Offshore service vessels (OSVs) are becoming larger, more specialized and technically sophisticated as a result of the rising demand for more complex deepwater field developments. Currently there are some 2,500 OSVs worldwide, with a steady growth projected from now through 2020.

All these has led to an expanded definition of OSV which refers to "not only traditional supply boats, but also anchor handling tug/supply ships, well stimulation ships, and standby ships" and even those "built to carry hazardous and noxious substances, to fight fires, or to occasionally recover oil."
"It is now commonly recognized that the design and normal operation of such ships differ significantly from those of general cargo ships. Therefore, comprehensive international regulations are needed that take specific account of the practical demands of these ships," Rathje pointed out in his presentation. In 1981, the International Maritime Organization (IMO) adopted Resolution A. 469, the first document that specifically addressed OSVs, plus ensuing resolutions to treat issues arising from increased operational complexity and technical advancement.

"However, these resolutions are often voluntary or confusing when applied to OSVs or do not go far enough."
A generic class notation of "Offshore Service Vessel" will be assigned to seagoing ships that are specially designed for support service to offshore installations. "Basic requirements regarding materials, intact and damage stability, design loads, and structural strength shall apply to any OSV type", said Rathje.

Also the ship's hull arrangement including deckhouses and windows, cargo handling arrangement and towing equipment is covered by the generic class notation. Owing to the broad operational profile of OSVs, Mr. Rathje suggested additional task specific notations, namely, HNLS (carrying hazardous and noxious liquid substances), AH (anchor handling), WS (well stimulation), Fire Fighter, Standby (standby and rescue) and Oil Recovery. Taking as an example the cargo handling arrangement of ships that occasionally handle, store, and transport recovered oil from a spill shall comply with special requirement dedicated to oil recovery.

The new rules also aim to address practical constraints that contradict regulations for the design of guard rails, double bottom, stern tubes, bridge visibility, navigational lights, etc. For instance, the collision regulations (COLREGs 1972) require ships greater than 164 ft in length to be equipped with both a forward and an aft masthead light, with a horizontal distance between them of at least half the ship's length. But most OSVs are in the 60 to 70 m range. The solution would be to "place the aft mast somewhere on the cargo deck". This is obviously impractical for crane operations. Supportive measures to apply for exemptions in such cases are outlined.

"Prescriptive class rules do require supportive assessment regarding certain safety related design issues, such as operations in severe seas that may adversely affect the ship's controllability, causing loss of stability," said Rathje. As a complementary measure, computational fluid dynamics (CFD) based numerical simulations can predict the behavior of an OSV operating in severe seas and assess safety aspects beyond the scope of standard class rules. "It has proven to be an essential tool for future rule developments," he concluded.


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