7th Experiment.
Torpedo:—As in the 5th experiment. It was placed on the ground, immediately under the edge of the outer bottom, 39-3/4' from the target, and opposite No. 18 frame, 70' from the stern; 50' below the surface of the water.
Effect of explosion:—Outer and inner bottom broken entirely asunder at No. 19 frame on the starboard side, and between Nos. 16 and 17 on the portside. A fracture was caused in the outer bottom extending from the shelf plate to upper edge of strake next the keel on the starboard side, and from the shelf plate to upper edge of flat keel plate on the port side. A fracture was also caused in the inner skin extending from the topside to the outer edge of the garboard strake on the starboard side, and from the topside to upper edge of garboard strake on the port side; this including a fracture of the keel at No. 17. The vertical keel, the longitudinals, as well as numerous bracket plates and angle irons, were broken, and about 2000 rivets in the outer bottom were rendered defective.
The outer bottom was indented over a considerable length, the indentation being greatest between the frames, and the maximum being 8 inches. The inner bottom was not indented or damaged, with the exception of the fractures before mentioned.
Experiments at Pola, Austria, 1875.—These experiments were carried out to determine the effect of very heavy charges of dynamite on an iron pontoon fitted with a double bottom, similar to that of H.M.S. Hercules.
Target:—An iron pontoon 60' long and 40' beam, with circular ends and fitted with a double bottom, also a condenser and two Kingston valves.