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         figure 12, or at another location. The drawworks 22 includes a
         rotatable drum 26 (figure 13) that can reel in and reel out the
         hoisting line (or lines) 20 wound on the rotatable drum. Each
         hoisting line 20 can be reeved over a sheave in a crown block
         24 coupled to the derrick 14 and connected to the supported
         load so that the reeling in and reeling out of the hoisting line
         20 via the drum 26 raises and lowers the supported load.
           In at least some embodiments, the hoisting system includes











                                                              Figure 15: Second example of a hoisting system.
                                                              heave of the vessel 12. In at least some embodiments, the ac-
                                                              tive heave compensation system 34 uses the measured heave
         Figure  13: Hoisting  system having  both active and passive heave
         compensation functions.                              to actively compensate for heaving motion through control of
                                                              the drawworks 22. For instance, the active heave compen-
         both active heave compensation and passive heave compen-  sation system 34 can include a controller (e.g., a program-
         sation to compensate for heaving motion of the floating ves-  mable logic controller  or a programmed  general-purpose
         sel 12 from wave action at the surface of the water. One such   computer) that receives the measured heave as an input and
         embodiment is generally depicted in figure 13 by way of ex-  controls operation of the drawworks 22 to raise and lower
         ample. In this figure, a load 30 is supported by a hoisting   the load 30 (with respect to the drill floor) to compensate for
         system including the crown block 24 and the drawworks 22   the heaving motion. The controller can control operation in
         with the rotatable drum 26. As described above, one or more   any suitable manner, such as by sending command signals
         hoisting lines 20 can be wound from the drum 26 and reeved
         over the crown block 24 to support a given load 30. Although
         not depicted here, it is noted that the hoisting lines 20 can be
         coupled to the load 30 by a traveling block suspended from
         the crown block 24 with the hoisting lines 20. But the travel-
         ing block is omitted in some embodiments. As the load 30 is
         suspended from the crown block 24 with the hoisting lines
         20, heave of the vessel 12 causes the load 30 to move up and
         down with respect to the underlying seabed. During drilling
         operations, such movement can cause a drill bit at the end of
         the drill string 18 to be pulled off the bottom of the well (with
         upward heave) or to be pushed with greater force against the
         bottom if the well (with downward heave).
           To compensate for the heaving motion and reduce devia-
         tion of the hoisted load 30 with respect to the seabed, the
         hoisting system in figure 13 includes an active heave com-
         pensation system 34 and a passive heave compensation sys-
         tem 36. A motion reference unit 32 can be used to detect the
                                                              Figure 16: Third example of a hoisting system.

                                                              to motors of the drawworks 22 that control rotation of the
                                                              drum 26. These motors can be considered part of the active
                                                              heave compensation system 34 as well.
                                                               The  passive heave compensation system  36 can  also be
                                                              used to counter heaving motion of the vessel 12. In contrast
                                                              to the active heave compensation system  34, the passive
                                                              heave compensation system 36 can counter heave without
                                                              requiring  external power.  For example, the passive heave
                                                              compensation system 36 can include one or more hydraulic
                                                              devices (e.g., hydraulic cylinders or hydraulic motors) that
                                                              passively store and release energy from the heaving motion
                                                              of the vessel 12 to move the load 30 with respect to the drill
                                                              floor to reduce the deviation of the load 30 from its position
                                                              with respect to the seabed. In some instances, the passive
                                                              heave compensation system 36 could also include an active
         Figure 14: First example of a hoisting system.       component (e.g., a hydraulic cylinder that passively compen-

         58     Wire Rope News & Sling Technology   April 2017
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