PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 566 



In order to propel the vessel with speed, and at the same time 

 turn her rapidly, two screw propellers are located at the opposite 

 sides of the vessel, upon a plan lately patented to the projector. 

 The propeller blades are mounted upon a hollow shaft, iitted at 

 its ends with gudgeons which enter into sponsons, n n, secured 

 upon the vessel's sides. Tlie cranks of the engines are secured 

 to these gudgeons, and turn into the sponsons ; and the connect- 

 ing rods extend directly from the steam cylinders, through open- 

 ings in the sides of the vessel, into the sponsons. The entrance 

 of the gudgeons into the sponsons is packed in the usual manner, 

 to prevent leakage. By this arrangement, each i)ropeller is 

 driven by two steam engines, as shown in Fig. 4, in the same 

 manner as the driving axle of a locomotive ; and as the pair of 

 engines of each propeller are entirely independent of those, of the 

 other, one propeller may be turned forward and the other back- 

 ward, to turn the vessel upon her centre so as to present her 

 beak always toward an adversary. The engines are extremely 

 simple, l^eing plain horizontal engines, each having its air pump 

 driven by a piston rod extending out of the butt of the cylinder. 

 The condensers, c c, and air pumps thus lie at the centre of the 

 vessel, between the butts of the adjacent t^vo steam cylinders. 



In order to make the vessel sufficiently strong, her bottom is 

 made cellular, and the interior of the vessel below the gun-deck 

 is divided by longitudinal and cross bulkheads into numerous 

 ■water-tight compartments, as shown at Fig. 2. The boilers, h h 

 b b, are six in number, and each is placed in a separate compart- 

 ment. The coal is stowed in the compartments d, outside of the 

 boilers, so that it is within reach of the firemen. These coal 

 bunkers are of sufficient capacity to contain 1,400 tons. The 

 engines require only 24 feet of the length of the vessel, and each 

 two are placed between water-tight bulkheads at a a. 



The armament is to consist of twenty-four guns of eleven inches 

 bore, placed on the gun-deck at the dotted line i i of Fig. 1, eight 

 feet above water, and sheltered by the sloping sides of the vessel. 

 With the draught of twenty-two and a half feet, the vessel can also 

 carry two twelve-inch rifled guns for solid shot, placed in revolv- 

 ing towers on her spar-deck, upon the plan which was adopted in 

 the Monitor. The armor plates are to be of solid rolled iron, 

 four and a half inches thick ; this thickness, when placed on a 

 slope, having been found by experiment sufficient. The dimen- 

 sions of the propelling machinery are as follows : four cylinders 



