Washboard locking device

My 430e has 1 wash board and a hatch over the top with just a pin that drops through the edge of the hatch and a padlock goes through that to lock it from the outside only. Im going for Catagory 4 (offshore) certification which requires the washboard to be able to be locked into the hatch and opened and locked from inside and out. Has anyone been through this? If so what solution/ product did you use?

Hi Angus - see pic above.  I made these  to meet cat 5. The latch pin slots into the same hole as the pin that you have.  You access the latch by removing the access lid.   The lanyards attaches to the inside grab handles.   The washboards are  marine ply - there's angled edge where they meet. 430e.