This paper describes a series of physical model tests carried out on a model of a jacket structure with a horizontal deck. The deck was represented by a closed rectangular box-shape structure with no support members. The dynamometer measured vertical and horizontal forces as well as moments about the transverse axis. The model was subjected to both regular waves and wave groups selected from irregular wave spectra. Wave spectra were modelled using a deterministic approach which matched the spectrum shape. The measured waves were scanned to identify groups containing waves with crest heights expected to make contact with the deck. A zero-crossing analysis was run on the measured wave groups to determine their period and crest heights. The model was then subjected to a regular wave having the same period and crest height.