It is a pretty simple process if you are reasonably handy. It may be complicated by what your previous owner did but it is hard to comment on that without pictures. Here's a good description of the process. Installing Hatches and Deck Plates by Don Casey
03-30-2008 05:49 AM
Installing a hatch...
My Cal 20's hatch over the V-berth was sealed up by a previous owner, and I would like to install a new hatch so I can do some overnights on the boat. As it is, a little more air would be needed to spend any length of time below. Any advice on installing a hatch? I have never done one before.