The device comprises at least one pair of flexible ballasts which extend laterally along the length of the inflatable structure and each comprise an orifice, acting as a vent, situated at the front, and a scoop system situated at the rear. Between the ballasts, at least one pipe connects the cavities of said ballasts to equalize their level of fill and the stagnation pressure of the water obtaining in said cavities when the inflatable structure is pulled along in the inflated state. This scoop system consists of a component moulded in a rigid or semirigid thermoplastic or is made of an assembly of cutouts from a flexible material of watertight fabric. This scoop system is bonded and/or welded to the ballast.