Reducing the added resistance in waves has become a crucial aspect of today’s ship design. The added resistance in waves is traditionally considered proportional to the square of wave height. However, this assumption is believed to be only partly valid, and further investigations are required. In the present study, experimental tests and numerical simulations were carried out to determine the added resistance in regular head waves of the DTC hull (the scale factor is 135). The numerical analysis was performed with SHIPFLOW 7.01, and the experimental campaign was carried out in the ETSIN-UPM towing tank. The investigation revealed that the added resistance in waves was not proportional to the square of the wave height, and a better correlation was obtained by changing the power of the wave weight to 1.75. Furthermore, an unexpected double resonance phenomenon on the added resistance was found at a Froude number of 0.13. The study also revealed an acceptable agreement between the numerical simulations and the experiments, except for the double resonance phenomenon.