Hinge mechanism

An arrangement for the raising and lowering of a mast, which comprises an upper mast portion and a base, wherein the upper mast portion is rotatable about a horizontal pivot axis, located in the base of the mast, the arrangement comprising:

• (i) docking means for restraining the upper mast portion against rotation;
• (ii) attachment for attaching drive means for driving the docking means between a first engaged configuration wherein the upper mast portion is restrained against rotation and a second disengaged configuration wherein the upper mast portion is free to rotate;
• and
• (iii) locking means selectable via an intermediate unlocked configuration between a first locked configuration wherein the docking means is engaged and a second unlocked configuration wherein the docking means is disengaged,
• characterized in that the locking means comprises a hinge mechanism which comprises first and second chock plates and an adjustable shaft, each of the chock plates including an aperture in the form of a figure eight having similar first and second circular portions connected by a neck portion of a width less than the diameter of the circular portions and the shaft is longitudinally adjustable between a first retracted position in which the sections of the shaft aligned with each of the chock plates have a cross-section which corresponds to the circular portion of the aperture and a second extended position in which the sections of the shaft aligned with each of the chock plates have a cross-section of a diameter which is less than the width of neck portion.