Robert,
The ram is that block at the bow:
http://en.wikipedia.org/wiki/CSS_Virginia
Here are some snips from the wiki above:
1.
"The hull's burned timbers were cut down past the vessel's original waterline, with just enough clearance to accommodate her large twin-bladed screw propeller; a new fantail and armored casemate were built atop a new main deck, and a v-shaped cutwater was added to her bow, which attached to the armored casemate. This forward and aft main deck and fantail were designed to stay submerged and were covered in 4-inch-thick (10 cm) iron plate, built up in two layers. The casemate was built up of 24 inches (61 cm) of oak and pine in several layers, topped with two 2-inch (51 mm) layers of iron plating oriented perpendicular to each other, and angled at 36 degrees from horizontal to deflect enemy fired projectiles."
From another site which I've lost, the citadel base was to be at the waterline, or a bit below and side armor was to extend 2' below the waterline. The side armor was 1" thick thanks to material shortages, it was supposed to be 3" iron.
http://cssvirginia.org/
This fan site (for want of a better term) appears to have some descriptive info that rings true.
Sort of a snip:
The Ram:
"The prow was of cast iron, wedged shaped, and weighed 1500 pounds. It was about two feet under water, and projected two feet from the stem; it was not well fastened."
Another site has the ram at 24' (feet) long. Looks like somebody passed on a typo...that's pretty common but hey, it's easy to type 24' or 24". Only mentioned because it showed up in a couple searches near the top of the site lists.
There's quite a bit more but it looks like WWII44's doing his homework. The drawing is agreeing with what's been published and it looks good!
CraigH