Floatover Categories:

The standard passive float-though method of installation, where the vessel enters between the legs of the support structure, is generally feasible to 35,000 MT. However, the characeristics of the vessel used change depending upon deck weight primarily:

• 0 – 12,000 MT: In this range, there are a large number of conventional barges available with leg spacing
• 12,000 – 22,000 MT: In this range, designs are typically toward the Black Marlin beam of 43 M. Other vessels have been modified to fit this dimension.
• 22,000 – 35,000 MT: In this range, stability augmentation or a T-shaped vessel may be required to maintain a 43 m leg spacing, but standard floatover is still possible.

The height of the Topsides Center of Gravity (CG) is ignored in this categorization for simplicity. In general, a high CG will move the deck up to the next higher deck weight category.

Despite general differences in vessels, many aspects of the installatin remain the same:

• Method: In random seas, floatover is conducted by a straight ballast down method. The deck enters the slot, aligns with the substructure supports, the floatover vessel is ballast to transfer, and then removed. In swell condition, a wider diversity of methods exist without a standard being reached.
• Hardware: Leg Mating Units (LMU) with elastomer deflection are used betwen the Topsides and Substructure to capture initial alignment (cones & receptors), then mitigate impacts and finally facilitate even load transfer under waves. Deck Support Units (DSU) with elastomer deflection may also be used where separation impacts are expected. Lateral load rings may be required for high seas, quarter or beam seas environments.
• Position System: In shallower water, a spread mooring system may be used. In deeper water, dynamic positioning may be required. However, in both instanced a secondary system of soft lines is generally used to control relative movement more tightly prior to initial dockwith with LMU's.
• Friction Fender: The Friction Fender is a motion suppression system that may be employed to extend the installation season or to conduct floatover in harsher environments and swells. more...

For more information on the details of methods and systems, please contact an Offshore Kinematics representative.