Ships at sea will encounter deck wetness events that usually are just annoying and rarely lead to damage. Discomfort is experienced by spray, as it is limiting view and hampering deck work. In freezing conditions, deck wetting will lead to icing. This study is a continuation of publications regarding the development of a marine icing model based on spray predictions, taking into account ship shape and the physics of wave run-up leading to spray jets. The modelling of jet development from wave run-up against a wall, representing a ship hull, is investigated by experiments and mathematical modelling using nonlinear wave theory. Run-up jets occur frequently for ships at sea and are responsible for most of the generated spray. Detailed measurements of the run-up jet were obtained from high-speed video registration yielding information on the droplet distribution. The measurements indicate that the thickness of the run-up jet above the wall determines the maximum droplet size, and that this size is significantly larger than generally assumed in icing models. Based on these insights, new computations are performed with the ‘SHIPICE’ marine icing model to demonstrate the applicability and accuracy of the approach.