Several patents are in use for a solution to provide this horizontal curve with a relatively small volume of gas.
It will be clear that these (kinematic) constructions can in fact only be used in a top-mounted heave compensator.
In this case, the largest part of the load is taken by the passive heave compensator and an extra active device, working in parallel, takes care of the increase of the load/heave curve and hysteresis.
The combination of PDSC (passive drill string compensation) and AHC (active heave compensation) are now in operation on the semi-submersible drilling rig Seadrill West Sirius (2008).
The compensation would then be performed by the hoisting device (Drawworks), that would pay out or feed in wire according to estimated rig position in according to seabed.