Deepwater developments have typically challenged floating systems to scale up for greater payloads, riser counts and drilling capabilities. There have been notable exceptions where more minimal solutions have been required. The Versabuoy system shows excellent scale-down capabilities, illustrated by the 1,250 ton payload system with a total hull structural steel weight (for all 4 hulls) of 2,800 tons. Note that the hulls are fabricated from rolled pipe with limited internal ring stiffeners which result in lower unit rate fabrication that multiple US Gulf Coast Fabricators can provide.  Multiple body motions analysis also shows the extreme wave response of this small system to be very close to that reported for the model test results for the larger unit. This allows SCR’s and umbilicals to be supported directly from the topsides.
An application under consideration for this scale of system is that of a Minimal Wellhead Control Platform (MWCP) for single or multiple wells tied-back to local deepwater infrastructure. This model calls for a MWCP to be located over the wells supporting a control and chemical injection umbilical and pigging riser. The MWCP supports an autonomous control system that can control well functions as well as redundant communication lines (microwave and satellite) back to the host. The default operating mode is with control from the onboard system. A pigging riser allows pigs to be pushed from the well to the host platform, removing the need for a round trip pipe loop. The platform is not normally manned and can operate autonomously for 7 to 10 days.
Cost and development schedule advantages for this system accrue from (1) a shorter control umbilical (2 to 3 miles from MWCP instead of 20 to 30 miles from host), (2) possible reduction of a pipeline leg and riser from host, and (3) reduced additional payload on the host (chemical injection and control equipment located on MWCP, one less riser on host). Recent proposals have shown this solution to be commercially attractive for a number of cases.
Design Catalogue for VersaBuoy MWCP with payloads 750 tons, 1,250 tons and 3000 tons in the Gulf of Mexico environment has been prepared. Key parameters of these designs are presented in Table 1.

Payload 750 ST                     Payload 3000 st

Table 1: VersaBuoy Minimal Wellhead Control Platform (MWCP)