First I want to respond to Larry Dunn's post of earlier today. His logic, as it turns out, is quite correct: apparently (if I'm reading Ron Mariner's description correctly) there was a layer of plating on top of the grating. I confess that was one possibility that hadn't occurred to me.
I imagine one result of the current work on the turret, engine, and other artifacts will be at least one new book on the Monitor, probably with updated plans. Even after Ron's excellent verbal description I'm still having a little trouble visualizing how the turret roof was built. The ship was built in a remarkably short time. To fabricate that rather complicated grating, only to cover it up with a layer of perforated plates, doesn't seem to make a whole lot of sense. I wonder if it's conceivable that the grating originally was the turret roof, and that the plates were added after the battle with the Virginia. We know the Monitor did undergo some minor modifications during that period - most notably the replacement of the damaged pilothouse. Maybe the same workmen modified the turret roof. That's pure, unsupported speculation on my part, though.
Regarding the structure of the hull - I can't help much. I gather the issue under discussion is the structure of the part of the hull (the "raft-like" part) with a rectangular cross-section that, in effect, overhangs the lower hull structure (the part with the tapered cross-section containing the engines, etc.). Many years ago, when I was working at the Mariners' Museum, I was lucky enough to arrange for the loan of a beautiful set of colored engineering drawings of the Monitor believed to have been drawn by the designer, John Ericsson. (That was one of the more satisfying things I accomplished during my time there. The drawings - actually one sheet of drafting cloth, with three cutaway views on it - were owned by the American-Swedish Historical Society, of Philadelphia. When I made the initial queries about the possibility of borrowing them, the answer was that they were too delicate to travel - and the American-Swedish Historical Society couldn't afford to have them conserved. We were able to work out a deal whereby the Mariners' Museum paid to have the documents treated, cleaned, mounted, and framed by one of the best labs in the business, in exchange for which we got to borrow them for several months.) I remember them as beautiful pieces of work, with lots of detail (though the structure of the turret roof was utterly ambiguous). But I honestly can't remember just how the structure of the overhanging portion of the hull was shown in those drawings.
I've had to spend more time than I'd like over the years staring at the photos and movies taken by archaeologists during the exploration of the wreck. And quite a few years ago I got hired by the Monitor Marine Sanctuary folks to design a paper model of the ship, to be used in conjunction with the organization's youth education activities. (It struck me at the time that the Monitor was an excellent subject to be represented in paper. She's one of the few naval vessels in history whose basic shape has no compound curves whatsoever.) When I was boning up on the subject prior to designing the model I looked at all the plans I could find. Most of them disagreed with each other on pretty fundamental points. The ones that were recommended to me most strongly were those by Alan B. Chesley. My recollection - which may be incorrect - is that they showed the bottom of the hull overhang as being covered with iron plates, like the rest of the hull. That seems to contradict the German drawing that was discussed earlier in this thread.
The movies and still photos of the wreck are, of course, hard to interpret in detail; so much of the old ship has either disintegrated or gotten covered with concretions that it's often hard to tell just what materials one's looking at. My general impression, though, is that the pictures confirm the Chesley drawings (as I remember them). I know for a fact that I drew the outlines of iron plates all over the bottom of the little paper model I designed. I ran a draft of it by John Broadwater, who at that time was the senior archaeologist working on the project; he corrected several small details, but didn't comment on the plating pattern. (John, then as now, was a busy man; it's possible that he missed something.) My inclination is to think the whole bottom of the ship is plated - including the underside of the overhang. I am, however, perfectly willing to be corrected on that point.
The basic question of why the rest of the ship hasn't been brought up, unfortunately, has a simple answer: money. The Navy, the Monitor Marine Sanctuary, the state of North Carolina, Duke University, East Carolina University, and heaven only knows how many other institutions have now been wrestling for more than thirty years with the problem of what to do with her. The technology probably does exist now to bring her up more-or-less in one piece. That would involve bringing a substantial chunk of the seabed up too - but it probably could be done. But it just isn't going to happen. I haven't kept up with the financial figures on the raising of the turret and the engine, but I believe the figure is well into the millions of dollars by now. And when the artifacts come out of the water the expenditures are just starting. The restoration, conservation, and preservation of such stuff is an ongoing - and expensive - process. Just getting that turret to the point where it can be exposed to the atmosphere on a regular basis is going to take several years - and who knows how many dollars and man hours. Even if the hull were brought up, I doubt that it would be possible to find the money to conserve and maintain it - and if it can't be conserved, it's better off where it is.
Over the years lots of ideas for dealing with the Monitor have been bounced around. There was talk of building an enormous cofferdam, stretching all the way to the surface, around the wreck and pumping the water out. At one time somebody proposed building a clear plastic dome on the seabed, with the wreck inside. (Tourists presumably would ride miniature submarines down to see it.) All of those ideas obviously got abandoned. And during all the years that the project was being discussed and debated, and the archaeologists were scrambling for every dollar they could get, the wreck was continuing to deteriorate. Now, not a lot is left. I suspect we won't see a great deal more of the Monitor come to the surface. But the good news is that what we have is utterly fascinating.