The models
Following exhaustive multi-body analyses and simulations a 6-week model test program was performed at the Offshore Model Basin, Escondido, CA.  Model testing was performed at a scale of 1:53. Four basic configurations were tested for Gulf of Mexico environmental conditions including 10 year winter storm, 100 year hurricane and 1,000 year hurricane (Hs = 62 feet), as well as loop current conditions.
The four configurations tested were based on a standard Versabuoy module with the following characteristics:

• Two level topsides each level 250 feet by 250 feet with a variable deck payload of 3,200 tons.
• The deck is supported by four “jacket” hulls on 125 feet centers.
• Each Jacket Hull has a total length 457 feet (design draft of 398 feet) comprising of 1,300 tons of hull steel and 2,400 tons of solid ballast. Each hull is fabricated from four 148-inch diameter tubular members on 27 ft centers running full length with cross tie members every 90 feet. Two of the cross ties supports a conventional heave plate.
• 8-leg catenary mooring system (2 legs per hull) modeled using OMB’s SMART system.

The modal analysis of this single module showed a system deck heave period of 27 seconds and a deck pitch/rill period of 34 seconds. Plate 6 shows a Single Module in the Wave Basin during storm wave conditions. The model testing program considered a single module, Two Modules combined to form a single 250ft by 500ft module, and Four Modules combined to form a single 500ft by 500ft module.

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Model Test Jacket Hull Configuration

Single Module in the Wave Basin

Two Modules in the Wave Basin
Click below to watch Module Videos
    

Four Modules in the Wave Basin

The Results
The following 3-hour extreme responses were measured during model testing.

These levels of response compare extremely favorably with all other classes of offshore floating development systems. An additional benefit is the low drag loads for the selected jacket hull which results in mooring loads of 30% to 40% less than of these for other classes of system for the same displacement. Finally, wave run-up seen on columns and hulls for other systems (reducing local air gap) was not seen for the Versabuoy system.