<p>Numerical and experimental results are presented for the vertical motion of a membrane-based floating solar island. The structure consists of a circular elastic torus with a floating membrane attached within. The work builds on an earlier study, where a linear model of the two-body system (floater and membrane) was presented. The novelty of the present research is twofold. First, a new theoretical model for the connection between membrane and floater is proposed, enforcing satisfaction of the kinematic constraint of the system, while at the same time modeling the contact force in a physically accurate way. This is done by introducing a new modal decomposition of the membrane’s vertical motion. Two approaches for the choice of modes are presented. Numerical results from the two methods show good agreement with each other. A comparison with the previously applied Lagrangian multiplier technique reveals a significant decrease in the estimated contact forces. Convergence with respect to the number of modes is demonstrated. Second, a new series of wave tank experiments have been conducted to further investigate the response of the structure in regular waves, with a new model of scale 1:50. Tests were conducted for a range of incident wave frequencies. Experimental point RAOs compare well with estimates from the theoretical model.</p>