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

The present invention reduces loads and saves steel on topsides (110) and grillage (125) of a catamaran system (100) by creating an upward, lifting force from a barge (115) to the topsides to offset a sagging bending moment of the 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 upward force 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 or other offshore structure.