(57) Motion compensating apparatus maintains a tension load on a marine riser supported
from a floating platform which is subject to movement by wave action and the like.
Bending movements induced by the roll and pitch of the vessel are decoupled by a resilient
bearing member (38) having an annular section of a substantially spherical or conical
laminated body of superposed layers of an elastic material (74) and a relatively inelastic
material (76). A tension load is applied to the riser by a hydraulic actuator (40)
which is supported by the resilient bearing member (38). The actuator includes a displacement
compensating cylinder chamber (55) having an adjustable volume of hydraulic fluid
presented to a piston (52) in the cylinder for supporting the upper end (72) cf the
manne riser. The displacement of fluid in the cylinder (55) varies in response to
the heave of the vessel to maintain a positive lifting force on the marine riser.
An accumulator assembly (88) is connected to the pressure chamber (55) of the hydraulic
actuator for supplving hydraulic fluid to and for receiving hydraulic fluid from the
pies- sure chamber in response to changes in its volume. Hydraulic fluid leakage past
the actuator seals (56 60, 67, 68) is monitored through a fluid circuit (65. 84) including
pressure switches (95. 97) and leakage flow indicators (103, 101).
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