In a first approximation, the vertical acceleration associated with pitch motion can be considered as the main cause of motion sickness, which is without a doubt one of the most unpleasant disadvantages of maritime transport. The reduction of motion sickness can be stated as a monovariable regulation problem of a highly perturbed system. This work presents the design of a monovariable robust controller with quantitative feedback theory (QFT) for reducing the vertical movement on a high-speed ferry. The different stages of QFT methodology have been done with the help of the software tool QFTIT (Quantitative Feedback Theory Interactive Tool). This is a free software tool that is characterized by its ease of use and interactive nature. The designed regulator is validated experimentally in sea behaviour trials with a scaled down replica 1/25 the size of a high-speed ferry. The designed regulator is also compared with a gain-scheduling scheme using a proportional and derivative controller (PD).