Abstract: The chock system has a plurality of teeth that are moveable individually generally parallel with a leg rack of a jack-up rig unit for pre-locking alignment with the rack teeth pitch, and as a group into and out of locking engagement with the leg rack so that accurate and positive engagement can be made by each of the teeth with the mating root between adjacent ones of a plurality of leg rack teeth.

Abstract: The self-locking chock system has a plurality of pawl cams grouped in a sequential alignment along a support member that is substantially parallel with a leg rack of a jack-up rig unit. Each of the cams is pivoted about a pivot axis that is on the common alignment axis of the support member, and is forced to ride upon the leg rack by a center of gravity located outwardly from the alignment axis on the side opposite that which rides on the leg rack. The cam profile is adapted to ride along the leg rack profile when the relative motion between the leg rack and the support member is in a first direction. When the relative motion is in a direction opposite to the first direction, the cam profile complements the leg-rack profile and under the weighted urging of the cam, the cam profile engages the leg-rack profile and enters into a positive, self-locking engagement that restrains further relative motion between the leg rack and the support member at least in the opposite direction.