Preloading to reduce loads and save steel on topsides and grillage of catamaran systems

Abstract

The present invention reduces loads and saves steel on topsides and grillage of a catamaran system by creating a counteracting moment to offset a sagging bending moment of its self-weight on the topsides during transportation. The present invention can reduce the span of the supports on the topsides on the catamaran float-over barges and move the reaction forces toward inner edges of the float-over barges. The counteracting moment can cause a reduction of stress on the topsides' and grillage's members caused during the topside offloading and transportation. The stress reduction can result in the members withstanding the additional dynamic load caused by a catamaran system without increasing member sizes adequate for an offloading operation. The reduction results in a significant savings, given the size of a typical topsides for a Spar hull.

1 . A method of preloading a catamaran system to reduce loading and material on a topsides for a Spar hull, comprising:
 transferring a topsides having a weight onto at least two float-over barges;   coupling the topsides with the barges to create the catamaran system; and   adding a ballast to the barges to at least partially counteract a sagging bending moment caused by the weight of the topsides.   
   
   
       2 . The method of  claim 1 , further comprising transporting the catamaran system to a location for installing the topsides on the Spar hull. 
   
   
       3 . The method of  claim 1 , wherein adding the ballast to the barges comprising adding the ballast outwardly from a lateral center of gravity of the barges. 
   
   
       4 . The method of  claim 3 , wherein adding the ballast comprises adding the ballast along the length of the barges. 
   
   
       5 . The method of  claim 1 , wherein coupling the topsides with the barges comprises coupling the topsides to a grillage system mounted on each barge. 
   
   
       6 . The method of  claim 5 , wherein coupling the topsides with the grillage system comprises coupling the topsides at a location that is near a lateral center of gravity of the barges. 
   
   
       7 . The method of  claim 6 , wherein adding the ballast to the barges comprises adding the ballast outwardly from a lateral center of gravity of the barges in a direction distal from the topsides coupled between the barges, the weight of the ballast at a distance from the lateral center of gravity at least partially counteracting the sagging bending moment. 
   
   
       8 . The method of  claim 5 , wherein coupling the topsides with the grillage system comprises coupling a locking plate at least partially around a guide pin installed on the topsides, the grillage system, or a combination thereof to maintain a lateral coupling of the topsides with the grillage system. 
   
   
       9 . The method of  claim 5 , wherein coupling the topsides with the grillage system comprises coupling at least two braces between the topsides and the grillage system, the barges, of a combination thereof, the braces being disposed inwardly from a lateral center of gravity of the barges. 
   
   
       10 . The method of  claim 9 , wherein coupling the braces between the topsides and the grillage system, barges, or a combination thereof comprising preloading the braces in a compressive load by adding the ballast to the barges prior to transporting the catamaran system to the location for installing the topsides. 
   
   
       11 . The method of  claim 1 , wherein coupling the topsides with the barges comprises hingeably coupling the topsides with the barges to allow adding the ballast to the barges to at least partially counteract the sagging bending moment. 
   
   
       12 . The method of  claim 1 , wherein adding the ballast to the barges comprises pumping fluid into one or more tanks on the barges. 
   
   
       13 . The method of  claim 1 , wherein adding the ballast to the barges comprises adding solid ballast to the barges. 
   
   
       14 . The method of  claim 1 , wherein the lateral center of gravity is disposed along a lateral centerline of each of the barges. 
   
   
       15 . The method of  claim 1 , wherein the barges collectively comprise sufficient buoyancy for a weight of the topsides, weight of the barges, weight of the ballast, and wave load during transporting the topsides to the location for installing the topsides. 
   
   
       16 . The method of  claim 1 , further comprising:
 positioning the topsides over the Spar hull; and   de-ballasting the Spar hull to transfer the topsides to the Spar hull.   
   
   
       17 . The method of  claim 1 , wherein adding the ballast comprises redistributing a weight of the barges to counteract the sagging bending moment. 
   
   
       18 . A catamaran system created for a Spar hull, comprising:
 a topsides adapted to be installed onto the Spar hull;   at least two float-over barges adapted to support the topsides, the topsides being coupled to each of the barges with the barges being spaced apart from each other, the barges comprising a ballast adapted to create at least a partial counteracting moment to a sagging bending moment created by the topsides on the barges.   
   
   
       19 . The system of  claim 18 , wherein the ballast is located outwardly from a lateral center of gravity of the barges in a direction distal from the topsides coupled between the barges, the weight of the ballast at a distance from the lateral center of gravity adapted to at least partially counteract the sagging bending moment. 
   
   
       20 . The system of claim  187 , further comprising a grillage system mounted on each barge, the topsides adapted to be coupled with the grillage system. 
   
   
       21 . The system of  claim 20 , wherein the topsides is coupled to the grillage system at a location that is near a lateral center of gravity of the barges. 
   
   
       22 . The system of  claim 18 , wherein the topsides is hingeably coupled with the barges to allow the ballast to at least partially counteract the sagging bending moment. 
   
   
       23 . The system of  claim 22 , wherein the topsides is hingeably coupled with the barges with a locking plate to maintain a lateral coupling of the topsides with the barges. 
   
   
       24 . The system of  claim 22 , wherein the topsides is hingeably coupled with the barges with at least two braces between the topsides and the barges that are bendable and disposed inwardly from a lateral center of gravity of the barges. 
   
   
       25 . The system of  claim 18 , wherein the ballast comprises liquid ballast. 
   
   
       26 . The system of  claim 18 , wherein the ballast comprises solid ballast. 
   
   
       27 . A method of preloading a catamaran system to reduce loading and material on a topsides for a Spar hull, comprising:
 transferring a topsides having a weight onto at least two float-over barges;   coupling the topsides with the barges to create the catamaran system; and   applying a pushing-up reaction on the topsides to at least partially reduce a sagging bending moment by the weight of the topsides.   
   
   
       28 . The method of  claims 27 , further comprising transporting the catamaran system to a location for installing the topsides on the Spar hull.