The Bellerophon shows the same arrangement of keel and keelson with the addition of wooden bilge-keels secured lightly to the bottom plates by angle-irons. The framing of this ship, however, is of the type known as the bracket-plate system. The features of this system are the adoption of a double bottom and of angle-irons connected by bracket-plates instead of by solid forged iron-work. The web of the frame in this instance is much deeper, giving a large space between the outer plating and the bottom formed by plating the floor edge of the transverse frames. In the Warrior it will be noticed this plating only extended to the third longitudinal on each side, while in the Bellerophon it reaches to the wing-passage bulkhead. The transverse inner angle-iron is continuous from bulwark to bulwark, the outer one being in short lengths to allow continuous longitudinals. The upper angle-irons of the longitudinal frames notch down over the transverse frames, while the lower ones are continuous. The spaces between the bracket-frames lighten the assemblage a great deal, while the longitudinals, being of continuous plate like the inner keel, are lightened by having holes cut in them. In this manner large water-tight compartments are secured; for the inner keel, the third longitudinal, and the wing-passage bulkhead longitudinal are solid. The web just underneath the armor-shelf is of the old-style solid plate, to give better support than would be gained by bracket-plates. The double-bottom arrangement continues throughout two thirds of the length of the ship, the frames outside of this being reduced in dimensions. The armor-shelf of the Warrior proving a weak construction, that of the Bellerophon was better worked. The outer angle was formed by an angle-iron bolted to the vertical outside plating, and to a flat plate forming the armor-seat, the iron being on the inside of each plate. This left an open joint between the lower edge of the plating and the upper edge of the side-plate, but the joint is one easily calked. [Illustration: Filled Wing-Passage of Hercules.] [Illustration: Floor of Hercules.] In the Hercules the bracket-plate system is quite similar, and additional strengthening was put in by partially filling the wing-spaces with a strake of heavy teak backing. Two box-keelsons were also run on each side of the main keelson, and the main keelson itself was strengthened by being carried up above the floor and braced by brackets on each side. The armor-shelf in this instance was also slightly modified. In the Invincible the wing-passage and its bulkhead is done away with, and in place of it the web of the transverse frame is deepened considerably, carrying the double-bottom arrangement up to the armor-shelf; and whilst retaining a good depth as security against the outer skin being broken by ramming, much space is gained in the hold.