Method and apparatus for the offshore installation of multi-ton packages such as deck packages and jackets

A method for lifting a multi-ton structure in an offshore marine environment, comprising the steps of:

• a) transporting a work platform to a desired site with a pair of barges that are positioned in spaced apart and generally parallel positions relative to one another, the barges providing a lifting assembly that support the work platform;
• b) attaching a lifting assembly to the multi-ton structure at multiple positions including positions that are at least on generally opposite sides of the multi-ton structure, and at upper and lower positions on the multi-ton structure respectively;
• c) the lifting assembly including a plurality of diagonally extending, inclined booms carried by the barges, the upper end of the booms supporting the work platform, the lifting assembly including a tensile cable member joining the barges to the combination of work platform and the multi-ton structure to be lifted;
• d) wherein in step “a” the booms are each connected by at least one lifting end portion to a receptacle on the work platform;
• and
• e) lifting the multi-ton structure with lifting lines depending from the work platform.

A method for lifting a multi-ton structure in an offshore marine environment, comprising the steps of:

• a) providing a work platform;
• b) attaching a lifting assembly to the work platform;
• c) wherein the lifting assembly includes opposed floating barges having diagonally extending lifting booms thereon connected at their upper ends with a lifting end portion to the work platform;
• d) structurally supporting each of the lifting booms at the lower end portion thereof with one of the barges, each boom being pivotally attached to its barge;
• e) wherein the work platform has receptacles thereon, each receptacle with a downwardly oriented recess that receives the lifting end portion of a boom as the boom inclination increases relative to the deck of the barge;
• f) supporting the work platform with horizontal chords extending between the barges and platform;
• g) providing drop blocks with lifting lines on the platform for selectively raising or lowering the structure;
• h) connecting the drop block lifting lines to the structure;
• and
• i) moving the structure to a desired elevational position with the lifting lines.

A lifting apparatus for lifting a multi-ton structure in an offshore marine environment, comprising the steps of:

• a) a work platform;
• b) a pair of barges that are positioned in spaced apart positions relative to one another, the barges providing a lifting assembly that supports the work platform;
• c) the lifting assembly including a plurality of diagonally extending, inclined booms carried by the barges, the upper ends of the booms supporting the work platform;
• d) powered lifting lines depending from the work platform that enable the multi-ton structure to be lifted.

A method for lifting a multi-ton structure in an offshore marine environment, comprising the steps of:

• a) providing a work platform;
• b) attaching a lifting assembly to the work platform, wherein the lifting assembly includes opposed barges having lifting booms thereon that are connected at their respective upper ends with a lifting end portion to the work platform;
• c) structurally supporting each of the lifting booms at the lower end portion thereof with one of the barges, each boom being movably attached to its barges;
• d) providing drop blocks with lifting lines on the work platform for selectively raising or lowering the structure;
• e) connecting the drop block lifting lines to the structure;
• and
• f) moving the structure to a desired elevational position with the lifting lines.