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* As the size of a jacket structure increases, it is built and transported on a

cargo barge in the horizontal position. The jacket is lifted off the cargo barge

using one or two cranes. Following pick-up, the cargo barge is withdrawn

and the jacket is upended. Single cranes with two blocks can be used for

upending smaller jackets with the jacket length aligned with the plane of the

crane boom. There are several methods of upending jackets:

* Two-block upending - upending in air or partially in water using two crane

blocks. In this method, the jacket does not have sufficient buoyancy to float

without crane assistance. Instead, the upending is achieved by hoisting down

the block of one of the two cranes while the other is hoisted up. Figure 4.2

shows a two-block upend operation. The size of the jackets that can be

upended with a single crane is limited.

Figure 4.2 – Two block upending

Single-block upending. A jacket installed using this method needs to have

sufficient buoyancy to float in the horizontal position by itself. In this method, the

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