A very long time ago PBO had a short article on building a hatch for a sailboat based on the Maurice Griffiths double coaming design. It was good albeit sparse on details but included all of the information one actually needed to build the hatch. I cut this picture out of the magazine and added it to my files...
Over the years I've come across a surprising number of folks building and repairing boats that seem to exhibit a pronounced lack of , for want of a better word, imagination. Then again, some might just call it laziness.
For me the above drawing of the hatch construction is really all one needs. It shows how it goes together and I don't have any issues with the fact that it does not tell me what glue to use, the type of hinges needed, or the thickness and type of wood used.
The fact of the matter is most details for the hatch are going to depend on the size of your boat, the size of the hatch, and what sort of materials you have available. Telling you that the hatch should be built of 7/8" stock is just going to cause you all sorts of problems if you don't have 7/8" stock available and, I suspect, that your local lumber yard will only have 3/4" stock anyway.
Of course, you could do what a guy I know did and order some teak from a shop a couple of thousand miles away, have it milled to a precise dimension of your choosing, and then shipped at ludicrous expense to where you are which will result in very nice but way-too-expensive hatches for the likes of us of a VolksCruiserish nature.
Sure details count but you really only need two things for a successful boat project and that's the general concept of how it goes together and, most importantly, the fact that the concept of the project actually works.
In the case of the Griffiths hatch it goes together like the drawing and thousands of hatches to this general design have been built and they work...
All you need to know.