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Doc. 31.-test of the mortar-boats.

Missouri Democrat account.

Cairo, February 9, 1862.
in respect to the efficiency of the mortar-boats constructed at St. Louis, at the suggestion of General Fremont, there have been many doubts in the minds of well-meaning persons, including a number of army and navy officers. They have been thought clumsy, insufficient in their bulwarks, incapable of bearing the heavy mortars designed for them, and beyond all question incapable of resisting the terrible concussion which would attend the firing of a thirteen-inch shell.

All these opinions and prognostications have been overthrown to-day, by the experiment made under the superintendence of Captain Constable, and before a committee of three, composed of himself, Capt. Kilty, of the gunboat Mound City, and Capt. Dove, of the gunboat Louisville.

One of the mortar-boats, No. Thirty-five, was taken in tow this morning, by three steam-tugs, and conveyed to a point a few hundred yards below Fort Holt, on the Kentucky shore. The huge mortar had previously been placed on board, and fixed upon one of Rodman's mortar-carriages or beds. Ten or twelve of the thirteen-inch shells were prepared, filled, however, with wet sand, instead of powder, the object of the experiment simply being to ascertain the range of the mortar, and the effect of the firing upon the various parts of the boat. The boat was fastened to the shore, and the mortar directed down the river, which from that point stretches away in a broad and straight sheet of water, five or six miles, toward Columbus.

Everything having been got in readiness, Capt. Constable fired a small charge of four pounds of powder, for the purpose of “scaling” the mortar. The first experiment with a shell then followed, with a charge of eleven pounds of powder. When all was ready, the boat was cleared of the company, most of us retiring to the shore, Captain Constable alone remaining to discharge the gun. Ready! fire! A deafening concussion, and in an instant the huge shell was seen mounting in the air with a magnificent curve, and its terrible roar gradually diminishing, as its distance from us rapidly increased. It may have risen to the height of half a mile, and was almost lost to view before it began to make its descending curve.

On its disappearance, our eyes were eagerly directed to the river's level, to mark its fall. It was wonderful to wait so long, the seconds lengthening out, as it seemed, to minutes. The suspense was relieved by the sudden shooting up, from the water's line, of a white column of spray, far down the Mississippi, and, as it was estimated, two miles and a half away from us. The mortar-boat was scarcely moved by the explosion, and the mortar-carriage recoiled but two or three inches. This was very encouraging.

The second experiment was made with twenty pounds of powder, Captain Constable again discharging the gun. The concussion was terrific. Some distance in the rear of the boat, where I was standing, it was not painful, but those who remained alongside and in the boat, were considerably shocked. The shell rose beautifully, mounting much higher in the air, and at the expiration of twenty-nine and one half seconds, struck the water, at an estimated distance of three miles. This concussion showed itself very palpably upon the boat. The hatchway-coverings in the front part were lifted off, and in some cases broken and split, while the boat itself recoiled some two or three feet, and penetrated the soft bank of the river.

Experiment number three was made with the full charge of twenty-three pounds of powder. The time of the flight of the ball was thirty-one seconds, and the distance three and a half miles. The recoil of the gun-carriage was about two feet, and the effect of the concussion upon the loose wooden work of the boat, was the same as in the previous shot.

Experiment number four gave results similar to number three, Capt. Paulding, of the gunboat St. Louis, discharging the gun in the place of Capt. Constable. Capt. Paulding describes the concussion as very stunning and painful, and thinks it could not be endured within the bulwarks of the mortar-boat by any man for more than eight or ten consecutive shots.

Number five was with but fifteen pounds of powder, the mortar in this case being elevated to more than forty-five degrees. The shell was twenty-eight seconds in the air, and seemed to fall as far away as any of the preceding ones, which led to the opinion in the minds of the Committee, that a lighter charge of powder was quite as efficient as a full twenty-three pound charge.

The mortar-boats are about sixty feet long, and twenty-five feet wide, surrounded on all sides by iron-plate bulwark, six or seven feet high. The mortar itself weighs seventeen thousand two hundred and ten pounds, has a bore easily admitting a thirteen-inch shell, and from the edge of the bore to the outer rim is seventeen inches. The mortar-bed weighs four thousand five hundred pounds, and from the experiment of to-day, is pronounced by Capt. Constable to be the most admirable mortar — carriage yet invented. The shell filled with wet sand, weighed two hundred and thirty pounds, an enormous missile, to be hurled through the air a distance farther than from the levee to Grand avenue, in your city. Filled with powder, these shell will weigh two hundred and fifteen pounds, and can be thrown at least half a mile farther than were those filled with the sand.

Say, twenty of these mortar-boats drop down to within easy reach of Columbus, and at the same time be out of the reach of the best rifled cannon the rebels may bring to bear — so small, indeed, at a distance of three and a half or four miles, as scarcely to be discernible on the surface of the water. Say further, that each of these boats will fire, at a very low estimate, four shells an hour, then twenty of them would discharge [119] eighty shells an hour, with perfect impunity, and at this rate, for one night of ten hours, eight hundred of these terrific missiles may be thrown into the rebel camp and fortifications. Can they endure it? Pandemonium would be a Paradise to the place it would make of Columbus.

The trial of to-day demonstrated that the recoil of the boat was altogether lateral, and not perpendicular, as it was feared it would be. It also shows that the iron bulwarks render the concussion more severe, than it would be without them; and that, if they are permitted to remain, some plan will have to be devised by which the gunners at each discharge, may get outside of them. Illustrating the effects of the concussion, is the circumstance that the cap of the gunner, who discharged the fifteen-pound charge, was carried away from his head, and he almost taken off his feet.

Another objection to the boat, discovered to-day, was its construction at the bow and stern. Unless towed very slowly, both up and down stream, it dipped the water considerably. These, however, are all minor objections, and easily got rid of. The boats will admirably serve the purpose for which they were designed, and prove the most terrible engines of destruction the enemy have yet had to encounter.

Yours, etc.,

G. W. F.

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Constable (6)
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