The rotations of a parametric pendulum fitted onto a suitable floating support and forced to move vertically under the action of water waves have been studied on the basis of a dedicated wave flume laboratory experiment. An extended experimental campaign has been carried out with the aim of providing insight into the mechanics of the pendulum’s response to the wave forcing and data useful as a benchmark for available theories. A large number of time histories of the pendulum’s angular position have been collected. Rotations have been detected for different values of the frequency and of the amplitude of the excitation, showing the robustness in parameter space, and for different initial conditions, showing the robustness in phase space. This experiment, suggested by the recently developed concept of extracting energy from sea waves, constitutes preliminary experimental proof of that concept’s practical feasibility.