Hydraulic power take-offs are nowadays among the first choices in power conversion systems for wave energy converters, mainly due to the high torques at stake, the low frequencies that characterise the prime mover motions and the power management achievable thanks to the implementation of accumulators and rectification valves. This work revolves around the implementation of a hydraulic power take-off on the ISWEC, a wave energy converter that exploits the gyroscopic effect on a spinning flywheel carried inside the hull to generate power from the waves. The main focus resides in the control of the transmission, an essential tool necessary to achieve consistent levels of power production in all the possible sea conditions.