Abstract The paper deals with hull damage in ships which are subjected to grounding actions. A ship is assumed to settle vertically on a rock. It is further assumed that contact actions are local and restricted to one plate section. The scenario is analyzed by conducting a series of panel indentation experiments. Various configurations of stiffened panels are loaded laterally by a cone shaped indenter until fracture occurs. The specimen dimensions represent a 1:3 scale of the dimensions found in medium sized tankers. Naturally, because damaged hull and cargo tanks may have severe environmental consequences, e.g. as exemplified by high profiled grounding accidents such as the Exxon Valdez grounding which lead to the discharge of nearly 240,000 barrels of oil, focus is on the plastic deformation and fracture resistance of the panel. This is Part I of a two part companion paper. This paper reports observations from the experiments. Part II–Numerical Analysis deals with the numerical simulations of the same tests. Although, the attention is primarily focused on ship grounding, the experimental results are of considerable relevance for other types of abnormal actions, e.g. ship–ship collisions, dropped objects on deck structures, and stiffened panels subjected to explosions or ice actions.