a boat body;

a driving source mounted on an inner side of the boat body, the driving source having a drive shaft which extends from one end thereof inside the boat body to an opposite end thereof outside the boat body;

a housing mounted on the outside of the boat body for turning movements between leftward and rightward positions relative to the boat body;

a screw bracket having an upper end connected to the housing for turning movements therewith;

a screw rotationally supported by a lower end of the screw bracket;

a connecting part having a universal joint outside the boat body which operably connects the opposite end of the drive shaft to the screw to allow the screw to be driven by the driving source so as to propel the boat body;

a servo mechanism housed within the housing and operably configured to turn the housing and the screw bracket mounted thereto between the leftward and rightward positions so as to positionally adjust the screw supported by the screw bracket and cause the boat body to turn leftward and rightward, respectively; and wherein

a screw adjustment mechanism configured to adjust tilt angle and depth of the screw, wherein the adjustment mechanism is centered around the connection part, and wherein the screw adjustment mechanism includes,

(i) first and second fixing brackets depending from the housing and defining a pair of opposed arc-shaped grooves wherein the upper end of the screw bracket is moveably interposed between the first and second fixing brackets;

(ii) at least one pair of protrusions extending outwardly from the upper end of the screw bracket and received respectively within the opposed arc-shaped grooves of the first and second fixing brackets, wherein

(iii) movement of the protrusions within the arc-shaped grooves causes the screw bracket to pivot about the connection part so as to allow the screw bracket to be moved to a desired tilt angle position and thereby adjust the depth of the screw.