An Investigation of Stability and Workability of ESEMI Under the Pre-Service Condition in Gulf of Mexico

This paper presents a global performance characteristics of an extendable draft semisubmersible (ESEMI) under the preservice condition in Gulf of Mexico (GoM) environment. The ESEMI consists of a deep draft semisubmersible hull with the second tier pontoon (STP) attached by eight extendable columns beneath the main hull. The STP is positioned just below the main pontoon bottom during the dock-side installation and the tow-out, and is installed once the ESEMI arrives at the in-place location. The STP increases vertical motion compared to the conventional deep draft semisubmersible when it is towed out, and the metacenter (GM) value keeps changing when the STP is lowered down. Typically, the GM becomes minimum value when there is a sudden change of water plane area, when the GM is supposed to be positive to assure the stability. The hydrostatic stability during tow-out and installation is investigated and is checked if it satisfies the criteria. The motions at tow-out and some typical installation stages are also simulated and discussed in the view point of workability.