A retractable stabilizing device for stabilizing a ship having a hull defined by a bottom having an opening (31, 32), said stabilizing device comprising: - a stabilizer fin; - a connecting body suitable to connect said stabilizer fin to the hull, said connecting body supporting said fin, said connecting body being rotatable together with said fin with respect to the hull between an extended position of said fin so that said fin projects from said hull through said opening (31, 32) into said bottom, and a retracted position of said fin so that said fin goes completely back into said hull through said opening (31, 32); - a first closing hatch integrally secured to the connecting body, said first hatch being suitable to at least partially close said opening (31, 32) when the fin is in said extended position, said first hatch being shaped with an outer surface thereof suitable to restore the shape and continuity of the bottom when said fin is in said extended position, characterized in that - said device comprising a second hatch integrally secured to the connecting body, said second hatch being suitable to at least partially close said opening (31, 32) when the fin is in said retracted position, said second hatch being shaped with an outer surface thereof suitable to restore the shape and continuity of the bottom when said fin is in said retracted position; and wherein - the first hatch and the second hatch are substantially equal to each other and arranged mutually angled according to an angle corresponding or substantially equal to the maximum angular displacement of the connecting body between a first angular position thereof corresponding to the extended fin and a second angular position thereof corresponding to the retracted fin. - a stabilizer fin; - a connecting body suitable to connect said stabilizer fin to the hull, said connecting body supporting said fin, said connecting body being rotatable together with said fin with respect to the hull between an extended position of said fin so that said fin projects from said hull through said opening (31, 32) into said bottom, and a retracted position of said fin so that said fin goes completely back into said hull through said opening (31, 32); - a first closing hatch integrally secured to the connecting body, said first hatch being suitable to at least partially close said opening (31, 32) when the fin is in said extended position, said first hatch being shaped with an outer surface thereof suitable to restore the shape and continuity of the bottom when said fin is in said extended position, - said device comprising a second hatch integrally secured to the connecting body, said second hatch being suitable to at least partially close said opening (31, 32) when the fin is in said retracted position, said second hatch being shaped with an outer surface thereof suitable to restore the shape and continuity of the bottom when said fin is in said retracted position; and wherein - the first hatch and the second hatch are substantially equal to each other and arranged mutually angled according to an angle corresponding or substantially equal to the maximum angular displacement of the connecting body between a first angular position thereof corresponding to the extended fin and a second angular position thereof corresponding to the retracted fin.