Memoir of John Ericsson

Memoir of John Ericsson

Before entering on a description of this fighting-machine I propose to answer the question frequently asked: What circumstances dictated its size and peculiar construction?

1. The work on the Merrimac had progressed so far that no structure of large dimensions could possibly be completed in time to meet her.

2. The well-matured plan of erecting a citadel of considerable dimensions on the ample deck of the razeed Merrimac admitted of a battery of heavy ordnance so formidable that no vessel of the ordinary type, of small dimensions, could withstand its fire.

3. The battery designed by the naval authorities of the Confederate States, in addition to the advantage of ample room and numerous guns, presented a
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formidable front to an opponent's fire by being inclined to such a degree that shot would be readily deflected. Again, the inclined sides, composed of heavy timbers well braced, were covered with two thicknesses of bar iron, ingeniously combined, well calculated to resist the spherical shot peculiar to the Dahlgren and Rodman system of naval ordnance adopted by the United States navy.

4. The shallow waters on the coast of the Southern States called for very light draught; hence the upper circumference of the propeller of the battery would be exposed to the enemy's fire unless thoroughly protected against shot of heavy caliber. A difficulty was thus presented which apparently could not be met by any device which would not seriously impair the efficiency of the propeller.

5. The limited width of the navigable parts of the Southern rivers and inlets presented an obstacle rendering manoeuvring impossible; hence it would not be practicable at all times to turn the battery so as to present a broadside to the points to be attacked.

6. The accurate knowledge possessed by the adversary of the distance between the forts on the river-banks within range of his guns, would enable him to point the latter with such accuracy that unless every part of the sides of the battery could be made absolutely shot-proof, destruction would be certain. It may be observed that the accurate knowledge of range was an advantage in favor of the Southern forts which placed the attacking steam-batteries at great disadvantage.

7. The difficulty of manipulating the anchor within range of powerful fixed batteries presented difficulties which called for better protection to the crew of the batteries than any previously known.

Several minor points familiar to the naval artillerist and naval architect presented considerations which could not be neglected by the constructor of the new battery; but these must be omitted in our brief statement, while the foregoing, being of vital importance, have demanded special notice.

The plans on pages 732-3 represent a longitudinal section through the center line of the battery, which, for want of space on the page, has been divided into three sections, viz., the aft, central, and forward sections, which for ready reference will be called aft, central, and forward.

Referring particularly to the upper and lower sections, it will be seen that the hull consists of an upper and lower body joined together in the horizontal plane not far below the water-line. The length of the upper part of the hull is 172 feet, beam 41 feet; the length of the lower hull being 122 feet, beam
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34 feet. The depth from the underside of deck to the keel-plate is 11 feet 2 inches, draught of water at load-line 10 feet.

Let us now examine separately the three sectional representations.