Linked-spar motion-compensated lifting system

An improved lifting system for operating a lifting cable over the side of a floating platform in which the pitch and roll of the platform and the motion of the water's surface are decoupled from the lifting cable, said lifting system comprising:

• a. a spar buoy having a narrow upper section with a relatively small cross-sectional area and a base section of a relatively large cross-sectional area, said spar buoy having a longitudinal channel for permitting passage of the lifting cable through the spar buoy;
• b. rigid boom means having an outboard end and an inboard end, said boom means being mounted to pivot forward of its inboard end on a first axis fixed relative to the deck of the floating platform to allow said boom means to rotate relative to the platform;
• c. a connect/disconnect gimbal sheave assembly means having a single sheeve free to rotate on its axle being rotatably and disengagedly coupled to the outboard end of said boom means to allow said gimbal sheave assembly means to rotate about a second axis which is normal to said first axis, said gimbal sheave assembly means also being pivotably coupled to the top of said spar buoy upper section to allow said spar buoy to pivot about an axis normal to the second axis and parallel to the first axis;
• d. said single sheave being positioned about said spar buoy so that a lifting cable passing over said single sheave will fall through the longitudinal channel of said spar buoy;
• e. a first means disposed at the inboard end of said boom means for letting out and taking in the lifting cable, said lifting cable extending from said first means for letting out and taking in over said single sheave means and through said longitudinal channel for connection to a payload;
• f. a second means disposed at the inboard end of said boom means for letting out or taking in a tension line, said tension line extending from said second means for letting out or taking in along said boom means to the outboard end thereof where it is connected to said connect/disconnect gimbal sheave assembly means;
• said tension line when let out allowing said gimbal sheave assembly along with said spar buoy to disengage from the end of said boom means;
• and
• g. said tension line when taken in causing said gimbal sheave assembly means and spar buoy to be pulled toward and become engagedly and rotatably coupled to the outboard end of said boom means and secured thereto when said tension line is held in tension.