This paper presents the concept of developing a surrogate model for the hydrodynamic interactions between heaving bodies including radiation wave effects. The surrogate model for an array of n heaving bodies is developed by creating an equivalent mechanical system that consists of n bodies in addition to other smaller intermediate bodies, springs, and dampers connected to each pair of the main n bodies. This equivalent mechanical system is designed such that the motions of its main bodies are the same as the motions of the actual array heaving bodies. The purpose is to develop dynamic models for wave energy converters (WECs) arrays that are more convenient to use for control design and optimization. The small moving mass that is connected between each two bodies in the surrogate mechanical system enables the modelling of the hydrodynamic interaction forces between the actual two buoys. A simulation tool is developed to simulate the motions of all bodies in the surrogate model. Also the motions of the actual WECs in the array are simulated using AQWA software. An optimization problem is then solved to minimize the error between the simulated motions of the WECs array in ocean, and the surrogate mechanical system. In this case study, the system design parameters to be optimized are: springs coefficients, dampers coefficients, and the additional body masses. Slack mooring dynamics are included in the derived equations of the motion of floating bodies. The proposed surrogate model is a time domain model that can be used for time-domain control design. The main advantage in the proposed technique is the ability to use a simple dynamic model for control design of arrays of wave energy converters. Simulations are presented that highlight the utility of the proposed model in control design.