What Jobs are Done with Dynamic Positioning? – Pt. 5

The fifth in our series of Dynamic Positioning job types. Make sure to check out the other entries in the series: Part 1, Part 2, Part 3, & Part 4.

Heavy Lift

This serious operation has a large potential for disaster should something go wrong.  Setting large suction piles or even an entire accomodation unit on top of a platfrom is a precision job that requires precise technology.

Heavy lift vessels can take a variety of forms, from a large derrick barge, such as J. Ray McDermott’s DB50, to heavy lift semi-submersible lift boats, such as those owned by Jumbo Shipping.

Semi-Sub Heavy Lift

This type of setup acts like a floating drydock, in that it gets under the load & then ballasts up.  The position of the ship with relation to the load is of critical importance if it is to be properly situated to take the support blocks.

So-called float in and float off ships are also known in which the floating cargo is floated into the ship’s cargo space in  tiers in order to avoid the disadvantages of the use of ship borne lifting devices.

Many of the larger ships of this class are owned by the company Dockwise, including the Mighty Servant 1, the Blue Marlin, and the Black Marlin. Two of the company’s vessels have been lost in recent years: the Mighty Servant 2 which capsized after hitting an uncharted underwater obstacle off Indonesia in November 1999, and the Mighty Servant 3 which foundered after unloading the drilling unit Aleutian Key offshore Angola in December 2006.

Crane Vessels

A crane vessel is a ship that specializes in lifting heavy loads & is equipped with a large capacity crane to that effect.  The highest lifting capacity vessels are generally semi-submersible or barge style vessels, although mono-hulls are also used.

In 1949 J. Ray McDermott had the Derrick Barge Four built, a barge that was outfitted with a 150 tons revolving crane. The arrival of this type of vessel changed the direction of the offshore construction industry. Instead of constructing oil platforms in parts, jackets and decks could be built onshore as modules. For use in the shallow part of the Gulf of Mexico, the cradle of the offshore industry, these barges sufficed.

In 1978 Heerema had two semi-submersible crane vessels built, the Hermod and the Balder, each with one 2000 ton and one 3000 ton crane. Later both were upgraded to a higher capacity. This type of crane vessel was much less sensitive to sea swell, so that it was possible to operate on the North Sea during the winter months. The high stability also allowed for heavier lifts than was possible with a monohull.

These days the growing move towards heavier lifting operations at increasingly greater depths is one trend that seems slated to continue into the future, along with the development of ultra-deepwater technologies to extend offshore crane capacity. MacGregor’s innovative fibre-rope technology, which overcomes the limits imposed by the weight of traditional steel wire at depth, and the state-of-the-art electro-hydraulic drive systems of Liebherr‘s new MTC 78000 crane are two such examples.

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