Bottom-hinged oscillating surge wave energy converters have been proposed in literature to extract energy from the surge wave motions. This study investigates a dual-flap out-of-phase floating oscillating surge wave energy converter (FOSWEC) for deep water deployment where the wave power density is larger and the WECs are less visible. The proposed FOSWEC consists of a floating platform and two pivoting flaps. The distance between the two flaps is around half of the wavelength in order to achieve out-of-phase motion, decrease the motion of the frame and reduce mooring load. Numerical modelling and dynamic analysis are formulated using the WEC-Sim. Numerical simulation results of the average power and optimal PTO damping with different viscous drag coefficients and PTO rotatory inertias are presented. Simulation results show the proposed dual-flap design can significantly mitigate the platform's horizontal motion so that the mooring load can be reduced. To experimentally evaluate the system performance, a 1:10 scaled prototype was designed, fabricated and tested in the wave tank based on the Froude scaling law. Experimental results were verified with modeling results and revealed the out-of-phase phenomenon as desired.