Abstract: The invention relates to a wave measuring instrument for use on a dynamically positioned or tethered floating vessel whereby to continuously monitor wave height, wave period and vertical heave of the vessel as the vessel responds to waves, swell and currents. The instrument comprises a measuring device connected to the vessel hull in a substantially submerged position whereby to continuously record the distance between the instrument and the ocean floor as the vessel heaves. A second measuring means automatically gauges and records the normally varying distance between the instrument and the water's surface, which distance results from the usual presence of wave action whether the latter be gradually rolling or relatively turbulent.The respective measurements thus obtained are thereafter integrated and compensated for to provide a relatively accurate record of the actual wave height between trough and crest, the wave period, and the vertical movement or heave of the vessel.