Liberty ships use the method described by Fred to secure the tarps. An interesting statistic courtesy of the WWII equipment inventory that starts to get across the amount of work involved: securing the hatch covers on a Liberty ship requires hammering down a total of 274 wooden wedges (these can splinter on occasion- 275 spares were to be supplied).
At least in the case of the Jeremiah O’Brien the hatch boards themselves were painted; the color appears to match the dark gray used on the hull. Boards that were unique to a hatch had a colored stripe (yellow for ‘tween deck, red for main deck) with the hatch number stenciled on top in black.
Hatch boards on the O’Brien are composed of three boards, with the middle one wider than the outer two. The handholds are half-round steel bar that run across a recess in the planking. The standard dimensions are 4'-11-3/4" x 2'-5-7/8" for the tween deck and 4'-11-3/4" x 2'-3-1/8" for the main deck. The reason for wider ‘tween deck boards is that the main deck has nine boards per row, while the ‘tween deck has eight. Some hatches have one or more rows of boards that are non-standard lengths.
Regards,
Chris Friedenbach
Crewmember, SS Jeremiah O’Brien