The modularized design and construction philosophy is a common practice for large onshore and offshore projects due to its opportunity for schedule and cost-savings. Multiple modules are fabricated at different construction yards across the world and then transported to service sites by marine transportation vessels. During transportation, the seafastening system is required to secure modules on transportation vessels. The seafastening system is designed to support the forces imposed on the module by accelerations, motions and deflections of the vessel, and distribute the concentrated forces from the module onto the vessel. The system reliability will depend highly on the forces for which the seafastening is designed.

The determination of the forces is typically based on decoupled analysis where the module and vessel are analyzed separately. The resulting forces are usually over-conservative. However, this paper presents a more advanced and accurate approach where interaction FE analysis is utilized to calculate the reaction forces. A light weight seafastening system is designed based on the calculated reaction forces. The system consists of a series of grillage beams with stoppers and wing plates welded to the vessel deck. Additional clips are used to restrain the module uplift. The proposed design allows for an easy and efficient seafastening removal, an optimum use of the vessel capacity and a reduction in fabrication costs. Results from a sample seafastening design are presented.

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