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Insights Paired-column semi-submersible | The power of ingenuity

A semi-submersible platform (semi) is a specialized offshore vessel that houses drilling rigs, safety vessels, oil production platforms, and heavy lift cranes. It goes without saying that semis need to be stable and have good seakeeping characteristics.

However, it can be difficult to achieve balance with conventional semis. To allow for motion they need to increase in depth and size, but the larger they become the more vulnerable they are to winds, waves and damage. This is a real disadvantage when developing oil and gas fields in harsh deepwater environments, like the Gulf of Mexico.


Oil & gas production needed to become safer and more financially viable in challenging waters. So we developed the Paired-Column Semi-submersible (PC-Semi). By adding one additional column per corner to the traditional semi, we had a system that could maintain stability in the severest of weather conditions.

We had our PC-Semi thoroughly engineered, model tested, qualified and approved by DNV for the Gulf of Mexico’s most severe metocean environment – the Central Region. Our more stable PC-Semi has made it possible to use ‘dry tree’ systems off the Gulf Coast. This means that rigs can now house their production equipment on more accessible surface platforms, rather than just operate ‘wet tree’ where their production ‘trees’ are all under water.

This new technology has brought many more advantages to deepwater developments:
• Reduced vertical motions allow conventional off-the-shelf riser tensioning equipment due to low riser stroke
• Full quayside integration
• Conventional structural components
• Efficient deck structure and hull deck interface
• De-coupling of wide column spacing (stability) vs. narrow column spacing (deck support)
• Steel catenary riser (SCR) friendly due to low surge motions and hang-off nearer to the platform centre
• Damage tolerance

“The Paired-Column Semi-submersible is the previously missing piece from a complete portfolio of deepwater platform concepts – a dry tree semi that can support drilling."

Our PC-Semi has made a big difference to communities in the Gulf of Mexico. It’s creating more work opportunities, is making energy more affordable, and has created a much safer work environment for rig personnel.

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