As floating wind turbines become more technically mature, the development of floating wind farms is under way. Cost-effective solutions are desired to reduce the mooring costs. The concept of a shared mooring system has been proposed for this purpose. This work presents a method to model the shared mooring system for a dual-spar configuration. By applying the theory in elastic catenary of cable structures, a shared line can be modelled. To verify the method, a dual-spar system is modelled in a multibody simulation tool, in which two floating wind turbines are connected via a shared line. Static analyses are performed by using the present method and the simulation tool. Further, a sensitivity study is applied to the shared line properties. Different mooring line properties have been investigated. The influence of the shared line properties is shown on the mooring restoring properties of the dual-spar system. The present modeling method can be applied in the preliminary design stage of shared mooring systems.