Abstract: Disclosed herein is a centering control type drill system for offshore structures. The centering control type drill system is installed to be elevated in a derrick for offshore drilling and rotates a drill string. The centering control type drill system includes a motor providing rotational force for offshore drilling, a gear box unit placed below the motor and increasing the rotational force of the motor, a main rotary shaft placed below the gear box unit and rotating the drill string; an intermediate bracket provided to the gear box unit, a dolly bracket disposed to be elevated in the derrick, a first dolly arm retractably coupled between the dolly bracket and the intermediate bracket by a hinge, a second dolly arm retractably coupled between the dolly bracket and the intermediate bracket by a hinge, and a cylinder rotating the second dolly arm about the hinge.

Abstract: Disclosed herein is a derrick lift system of an offshore structure. The derrick system can improve drilling workability by enabling safe and easy height adjustment of a derrick using an adjustment unit, and can improve structural stability by lowering the center of gravity of the derrick through the height adjustment of the derrick, as occasion demands.