These ships, being constructed for ramming, require a firmly braced stem. The stem itself is a solid forging, and attaches to the flat keel by a plain scarf, the outer keel-plate being carried some distance farther along the turn of the fore-foot than the inner one. The whole length of the stem is deeply rabbeted to receive the forward ends of the side-plates and armor, which all house in it. For a distance of forty or forty-five feet from the bow the bottom plates are doubled to give additional stiffness, each plate housing in a separate rabbet. The rear side of the stem is cut square, the breast-hooks seating fairly on it. Stern-posts are now invariably made in single solid forgings, and are plain scarfed to the keel as with the stem. Compartment bulkheads form an element of great transverse strength. There is no fixed rule for their application in war-vessels, but the usual number is seven. Of these, one is placed well forward, called the collision bulkhead, another is far enough aft to just enclose the screw-shaft stuffing-box, two others are respectively forward of the boilers and abaft the engines, and the others divide the remaining space as is best suited. Above the water-line, doors of a sufficient size to render free passage are worked in the bulkheads and are on hinges having clamps by which they may be screwed up water-tight. Below the water-line the doors slide either horizontally or vertically, being worked by gearing on the main-deck. The wing-passages are provided with small sliding doors generally kept closed. The compartments of the double bottom are connected by sluice-valves worked from the main-deck. These points constitute the main peculiarities of iron ship-building as it is at present carried on. There are constant modifications made in details, many of which are of the greatest importance, but a description of them would be out of place except in a work on iron ship-construction. _Iron Sheathed with Wood._