Experimental investigations on the hydrodynamic response of a spar and semi-submersible linked system under random waves are presented in this paper. Responses under regular waves were presented in Part I. These studies were performed for two cases: in the first case with the spar alone and the second case with a semi-submersible linked to the spar. The influence of the semi-submersible on the motion response of the spar and its mooring system are evaluated and presented together with acceptance criteria used in the industry. The responses are lower than allowable acceptance criteria limits, and the system is found to be stable in all mooring configurations both in survival and operating conditions. © 2012 Taylor and Francis Group, LLC.