Abstract: A device for reducing the resistance to the advancement on water of a motorboat (1), including a keel (2), on the underside of which at least one step (3) is provided; projecting element (6) for increasing the points of separation of the motorboat (1) from the water are provided at the step (3) and extend away from its free edge, on the projecting element (6) there acting the weight of the boat which is hence distributed over a greater number of points than those of the step (3), the projecting element provided regularity in the streams of air and water which flow below the keel (2) downstream of the projecting element, and creating a microvotex effect between the projecting element and the keel which contributes to the support of the boat, such that there is a smaller resistance to the advancement of the motorboat on water, with consequent higher boat speed.