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Semis

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AVCO-TS, Inc. has been involved with Semis since its very foundation and the latest projects were our creativity and technical ingenuity was in display was the Grupo R New Build Semis at DSME, Korea and Jurong, Singapore.

Sixth & seventh Generation Semis are the order of the day, these units are built with top of the line, state of the art equipment systems and can cost upwards of $700MM with a delivery schedule that can go up to 36 months, based on the features and delivery from the various companies providing systems and equipment for the unit(s).

Definition:   A semi-submersible is a specialized vessel used in a number of specific offshore roles such as drilling units, safety vessels, oil production platforms, and heavy lift cranes. They are designed with good stability and safety characteristics.

A semi-submersible obtains its buoyancy from a dynamic positioning system installed on board, a ballasted, watertight pontoons located below the ocean surface and wave action. The operating deck can be located high above the sea level due to the good stability of the design, and therefore the operating deck is kept well away from the waves. 

With its hull structure submerged at a deep draft, the semi-submersible is less affected by wave loadings than a normal ship. With a small water-plane area, however, the semi-submersible is sensitive to load changes, and therefore must be carefully handled to maintain stability; a semi-submersible vessel is never entirely underwater.

The Blue Water Drilling Company owned and operated the four column BW Rig No.1 in the GoM for Shell. As the pontoons were not buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught mid way between the top of the pontoons and the underside of the deck. It was observed that the motions at this draught were very small, and Blue Water Drilling and Shell jointly decided that the rig could be operated in the floating mode and this is the story behind the concept of floating drilling, made extremely popular and used worldwide since the early 70′s. The first semisubmersible was available in 1961 and the first drilling semi-submersible Ocean Driller was launched in 1963

The industry quickly accepted the semi-submersible concept and the fleet increased rapidly to 30 units by 1972.

Offshore drilling rigs have been classified in “generations” depending on water depth capability:

Generation Water Depth Est. Dates
First 600 ft 180 m Early 1960s
Second 1000 to 1500 ft 400 m 1969–1974
Third 1500 to 2500 ft 650 m Early 1980s
Fourth 2500 to 5000 ft 1250 m 1990s
Fifth 5000 to 8500 ft 2250 m 1998–2004
Sixth Beyond 10000 ft 3000 m 2005–2012

Other Work

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