Authors: Dr. Partha Chakrabarti, Mr. Ramesh Maini
Jack-Up rigs have traditionally been designed for Oil and Gas (O&G) drilling and production. At other times a jack-up has been used primarily for proving utilities such as Accommodation facilities, power and cranage to adjacent Platforms. Jack-up units are also being used for projects such as liquefaction of gas. Recently they are being designed and built as Wind Turbine Installation Vessel (WTIV) or Feeder Vessels to supply Wind Turbine components in the field. Jack-ups have also been used as a general service vessels known as “LIFTBOATS.” Recently built Jack-ups as WTIVs or LIFTBOATs have been self-propelled with large Cranes and large accommodations capacities. The designs of all Jack-up units are approved by Class Societies and are built for a selected Flag State. Since these vessels are extremely expensive, Marine Warranty Surveyors are employed to preserve their insurance. If these vessels have to be moved to a location far away from its current location, dry tow may be required. Marine Warranty Surveyors may define additional design limitations with considerations from the Dry Tow vessel company.
For design purposes these structures need a lot of information prior to starting the design such as:
· Detailed data of purpose including description of operating site(s); minimum and maximum operating water depths, possible operating locations in the world as well as maximum intended payload, POB, Crane capacities, Helideck, distance from shore, intended Class Society for design and construction approval, Flag state, etc.
· Time the jack-up will stay at the same location
· Environmental data for the location that should include wind, current and wave data including magnitude such as wind and current speed for different directions, maximum wave height and period for various return periods including scatter data for fatigue design
· Geophysical information to avoid problems with seabed pipelines, large boulders or chunks of debris, existing Spud Can holes or sudden change in seabed slope
· Geotechnical data for evaluation of Spud Can penetration, design associated fixity, and foundation stability including a review of probable punch-through concerns.
The most important development towards rules for design of jack-ups came by an initiative from SNAME by constituting a JIP the final result of which was the document SNAME 5-5A. This included the guidelines for design of jack-ups, its maintenance, going-on & off location precautions, etc. Finally, this gave rise to the International Code ISO 19905-1 and 19905-4. This gives the guidelines and regulations for O&G jack-up design for all the phases of its life. Recently, SNAME has initiated a JIP for WTIV Jack-ups.
Zentech is involved in all these design and construction aspects.
