In this study, we consider a novel method of sensing the motion of a wave energy converter in a wave tank under theinfluence of incoming waves. The wave energy converter considered in our research is an oscillating surge waveenergy converter, which is a hinged paddle that responds to incoming waves. Motion sensing is normally done withinertial sensors, which can hinder motion due to suspended cables that carry power and transmit signals. Our proposedmethod is contactless and can be implemented economically. A camera is used to record different marker patternsaffixed to the moving paddle and the motion deduced by pose estimation algorithms.Fiducial markers are commonly used for robot localization and in augmented reality. There are many types offiducial markers, including ArUco-type markers which are accurate, fast and robust. The system consists of markersattached to the paddle element and recorded using a machine vision camera. A pose estimation algorithm is thenapplied to the detected markers to estimate the tilt of the paddle. In this work, we examine the challenges of imageacquisition and calibration for underwater targets, compare the motion obtained by this new system with a calibratedtilt sensor and identify areas where the new system may be superior.