Stabilization system for a watercraft with a hull, comprising: - a stabilization fin rigidly connected to a shaft of the stabilization fin; - an actuator system comprising: a) a housing comprising a toroidal portion configured to be inserted in an opening of said hull, wherein the toroidal portion comprises means for fixing the housing to said hull, b) a reduction gear with hollow shaft, wherein said reduction gear comprises an output connected via a flange to said shaft of the stabilization fin and an input, and c) an electric motor (3, 4) with hollow shaft, wherein said electric motor (3, 4) is arranged in said toroidal portion and comprises a stator rigidly connected to said housing and a rotor connected to said input of said reduction gear, wherein said shaft of the stabilization fin passes through said electric motor (3, 4) and said reduction gear, and said electric motor (3, 4) is arranged between said reduction gear and said stabilization fin; and - a control system configured to receive data identifying the roll of said watercraft and drive said electric motor (3, 4) as a function of said data identifying the roll; wherein said stabilization system comprises an absolute encoder, wherein the body of said absolute encoder is rigidly connected to said housing and the input of said absolute encoder is coupled via transmission means to said flange, and wherein said flange has at least partially a contoured profile, wherein the stabilization system comprises a toothed rod, and wherein the stabilization system is configured such that a rotation of said rod rotates also said flange. - a stabilization fin rigidly connected to a shaft of the stabilization fin; - an actuator system comprising: a) a housing comprising a toroidal portion configured to be inserted in an opening of said hull, wherein the toroidal portion comprises means for fixing the housing to said hull, b) a reduction gear with hollow shaft, wherein said reduction gear comprises an output connected via a flange to said shaft of the stabilization fin and an input, and c) an electric motor (3, 4) with hollow shaft, wherein said electric motor (3, 4) is arranged in said toroidal portion and comprises a stator rigidly connected to said housing and a rotor connected to said input of said reduction gear, wherein said shaft of the stabilization fin passes through said electric motor (3, 4) and said reduction gear, and said electric motor (3, 4) is arranged between said reduction gear and said stabilization fin; and a) a housing comprising a toroidal portion configured to be inserted in an opening of said hull, wherein the toroidal portion comprises means for fixing the housing to said hull, b) a reduction gear with hollow shaft, wherein said reduction gear comprises an output connected via a flange to said shaft of the stabilization fin and an input, and c) an electric motor (3, 4) with hollow shaft, wherein said electric motor (3, 4) is arranged in said toroidal portion and comprises a stator rigidly connected to said housing and a rotor connected to said input of said reduction gear, wherein said shaft of the stabilization fin passes through said electric motor (3, 4) and said reduction gear, and said electric motor (3, 4) is arranged between said reduction gear and said stabilization fin; and - a control system configured to receive data identifying the roll of said watercraft and drive said electric motor (3, 4) as a function of said data identifying the roll;