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BS is supporting the development of alternative
semisubmersible designs that address deepwater motion issues
for Gulf of Mexico installation. One such design includes the
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center pontoon (CP) semisubmersible concept, developed by Sea Engineering
and MODEC, which provides a unique approach to problematic motion
challenges, says Pao-Lin Tan, ABS Chief Engineer.
“A low-motion semisub is attractive to deepwater operators
seeking increased stability for their production platforms. Our
independent review of the strength and stability of this hybrid
design found proven technology and sound engineering practices,
opening the door for fast-track development,” said Pao-Lin.
ABS approval in principle (AIP) is the first step in a full ABS
review of the design and classification of the semi-submersible
as a XA1 Floating
Offshore Installation.
Approval for the concept is in accordance with the ABS Rules
for Building and Classing Mobile Offshore Units
and the ABS Guide
for Building and Classing Floating Production Installations.
The CP semi design calls for moving the pontoons of a conventional
semi inward toward the center of the structure. Flowline and export
risers are supported on both sides of the pontoon, promoting long
fatigue life due to low-platform heave motion. The shorter pontoon
span between the four-corner column supports results in increased
stability when compared with more conventional semisubmersible hull
forms.
ABS expertise with mooring design contributed to the approval
of the novel concept, says Pao-Lin.
“Mooring for the structure can include either taut polyester
or steel semi-taut systems. Selection of the appropriate mooring
option reduces overall motion, leading to better equipment function
and enhanced safety and comfort for the personnel,” he said.
The proposed mooring system meets the requirements of the ABS
Guidance Notes on the Application of Synthetic Ropes for Offshore
Mooring.
CP semi design parameters are based upon hypothetical field development
projects in water depths of 4,300 feet to 7,500 feet. The concept
is being considered for use on deepwater discoveries such as BHP’s
Neptune in the Gulf of Mexico, says Pao-Lin.
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