clockwise closing motion of the crankshaft 12 and the crank link 13 the connecting link 14 turns about the pivot pins 15 and 15 39 which couple the connecting link 14 to the crank link 13 and the locking bolt pin 16 respectively thus converting the rotary motion of the crank link 13 to a linear motion of the locking bolt pin 16 as a result the locking bolt pin 16 moves radially inwardly as viewed relative to the axis of the hatch ring 2 transmitting a linear radial force to the locking bolt 11 with the intermediary of the spring washers 20 which undergo compression in response to the resistance to the radially inward motion of the locking bolt 11 such a resistance is generated by the camming action between a chamfered surface 22 of the locking bolt 11 and the bevelled surface 7 of the hatch cover 3 it is noted that the spring force exerted by the compressed spring washers 20 to the locking bolt 11 is at all times during the closing motion and during the closed state of the latching unit 4 greater than the force resisting it so that the resisting force due to the camming action between surfaces 7 and 22 will always be overcome by the resilient force exerted by the spring washers 20 in this manner a controlled resilient locking force urging the hatch cover 3 against the seat 6 by the camming action between the oblique surfaces 7 and 22 is ensured during the motion from the open position into the closed latching or bolted position as well as during the period the bolted position is maintained when the closed position of the latching unit 4 is reached.