Houston Offshore Engineering

Concept-neutral experience with every major technology used to support offshore facilities.

Semisubmersible

Semisubmersible Project Similar to the Truss Spar, the spread mooring of a Semi does not influence the wave-induced motions of the platform. The Semi relies on its small waterplane area to help minimize vertical motions. Vertical motions of the many typical Semi designs in the GoM prohibit the platform from supporting top tensioned risers.

Advantages of the Semisubmersible

Less sensitive to water depth than TLPs
Wide range of payload capacity
Installed as a fully integrated system
Maximum execution plan flexibility
Support of remote wells
Drilling and workover capability (using subsea BOP)
Can be easily redeployed

Limitations of the Semisubmersible

Platform motions
Cannot support TTRs (click here for dry tree Semi option)
SCR fatigue

The above mentioned limitations are general in nature. The critical objective when developing a Semi configuration is to minimize motions to meet functional requirements such as SCR support and processing up time.

The Semi is perhaps the least complex to integrate and install but the overall motions performance is less favorable than the Spar or TLP. The motions therefore have more impact to functional capability and performance.