Hello I have a under the counter weed hatch. I think that is how you refer to it. My narrowboat build date is approx 1980s. It has two bolts on either side them coming up from the underside of the top plate into the lid is a bolt that someone has put in and tapped off with a weld. There is approx 4 inches from water level to the top of hatch. Has anyone encountered this before and does it spell impending doom. I need to clear prop of somthing wrapped around it. Many thanks for ideas, information.