One of the most interesting viscous drag reduction techniques for a boat hull is the so called air lubrication. Although this method has been known for many years, it is scarcely applied in the shipbuilding industry, because it requires to re-design the hull bottom, to define and generate the artificial cavities where the air bubbles can be generated and supplied by using an airflow. It has been demonstrated that the drug reduction is more consistent on full form and slow hulls, where the viscous resistance component is the prevailing one. Recently, as found in (Sverchkov, 2010), it has been demonstrated that the drag reduction can be obtained also for planing hulls. But information regarding applications for semi-displacement hulls characterized by FN >=0.45 and FN<= 0.65, which are navigation conditions in which many boat hulls used for recreational activities operate, is more scarce. A series of tests have been carried out on some models, navigating in semi-displacement condition at the towing tank of the University of Trieste and the results will be presented and discussed (Pugnetti and Zotti, 2005)