Hugh Harding found that even on his mooring tucked away up a narrow dyke there was enough vibration, or movement, in his boat so that he regularly found that his fore hatch bolt had slid undone.
He modified a miniature shackle by removing the pin and substituting a bolt. Before fitting the screw to the shackle he screwed a nut tight up to the screw head to give a better grip for the fingers.
The replacement bolt is passed through the loop that normally prevents the bolt handle sliding completely out of the main shaft. With the screw tightened the bolt is locked shut. Release the screw and the bolt can be withdrawn to the open position