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UPPER AND LOWER GUIDES
All Jack Ups have mechanisms to guide the legs through
the hull. For Units with Pinions, the guides protect the pinions
from “bottoming out” on the rack teeth. As such, all Units are
fitted with a set of upper and lower guides. Some Jack Up Units,
which have exceptionally deep hulls or tall towers of pinions, also
have intermediate guides. These guides function only to maintain
the rack the correct distance away from the pinions and are not
involved in transferring leg bending moment to the hull. Guides
usually push against the tip (vertical flat side) of the teeth, but this
is not the only form of guides. There are also other forms of guides
such as chord guides, etc. Depending on accessibility, some guides
are designed to be replaced and are sometimes known as “wear
plates.”In addition to protecting the pinions and hull, all upper and
lower guides are capable of transferring leg bending moment to the
hull to some degree determined by the design. The amount of
moment transferred by the guides to the hull as a horizontal couple
is dependant on the relative stiffness of the guides with respect to
the stiffness of the pinions and/or fixation system (if any).
FIXATION SYSTEM
In line with improving the rig’s operational efficiency and
performance, the Self Positioning Fixation System (fig. 1.7) was
introduced to provide the rig with the increased holding capacity
required for almost any operational condition. The fixation system
is an electro-hydraulically actuated, high capacity self positioning
rack chock type system. Once engaged, the chocks are locked
against the leg rack by wedge blocks. The wedge blocks are held
by self-locking jackscrews driven by worm gears.
The rack chock tooth profile is specially designed to
provide smooth engagement and disengagement. The system can
automatically position the rack chock such that the
engagement/disengagement can be done regardless of the rig
elevation. This minimises human intervention and speeds up
operational time of engagement and disengagement.

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