After ballasting down, the barge is pulled out from under rig

Project Summary

In 2006, Argonautics Marine Engineering was involved in the tow-out of the semi-submersible drilling rig GSF Development Driller I from the Kiewit Offshore Services yard in Ingleside, TX, to deep water offshore.

The GSF Development Driller I was repaired at the yard after sustaining damage in hurricane Katrina. With its 8 DP thrusters installed under the rig pontoons, the total rig draft was the same as the water depth in the channels to open water. To ensure sufficient bottom clearance and avoid damaging these thrusters on the way out, the rig needed to be lifted for the tow-out. A solution was found by inserting a large cargo barge between the rig pontoons and partly deballasting it to provide the required 1.0 m lift - a modern version of the old "ship camels" used in Amsterdam in the 17-th century. Special support brackets with softwooden cribbing blocks were mounted to the barge hull, in line with strong stiffeners inside the rig's cross braces. Time domain analyses were performed to determine the limiting sea states for towing the combined units offshore and for the barge removal.      

On April 9, the GSF Development Driller I supported by the Boabarge 16 was towed out from the yard through the narrow La Quinta Channel and Corpus Christi channel to the offshore deep water site for removal of the barge. Early next morning, after confirmation that the good weather window was holding, the barge was ballasted until the rig was floating on its own and sufficient clearance was obtained between the barge supports and the rig braces. The barge was then pulled out from under the rig and deballasted for demobilization.

Scope of Work

The project scope included:

• Feasibility study comparing the various rig draft reduction options;

• Verify suitability of selected cargo barge;

• Design support brackets, guide posts, and cribbing arrangements;

• Provide all procedures, including ballast plans, weather limits, risk analysis, etc.;

• Provide on-site assistance during barge insertion and removal operations.

Time Domain Analysis Video

A short video showing the results of the MOSES time domain analysis for the combined units in 6 ft bow quartering seas. Requires Windows Media Player.

 Time domain analysis...  

Project Paper

A paper on this successful tow-out was presented at the 26th International Conference on Offshore Mechanics and Arctic Engineering in San Diego, CA, June 10-15, 2007...

Project Photographs

Boabarge 16 ready to be moved under the rig.	Rig braces supported by special brackets.	Bow of barge protruding out from under rig.	Rig with barge towed-out from the yard to deeper waters.