With an outer shell of aluminum bronze and an inner shell of the finest steel, the vessel combined great strength with a minimum amount of metal in its construction.
“Gentlemen, if you will follow me,” said Lieutenant Sibley, “I will show you over the vessel.”
Descending the companion-way, the entrance to which could be closed by an air-tight door, the party proceeded about the vessel.
Longitudinally and horizontally, from apex to apex of the cones, was a steel deck dividing the vessel into two equal parts. The first forty-five feet of each cone contained the tubes of compressed air and oxygen. There were in each end about 2,500 feet of five-inch steel tubes, one-half inch thick, containing over 4,500 cubic feet of air under a pressure of 1,500 pounds per square inch. This was sufficient, as Lieutenant Sibley explained, to sustain active life for the entire crew for two hours. “But we have other facilities,” continued the Lieutenant, “by which the vitiated air is deprived of its carbonic acid, and then recharged with the lipthalene gas from the receivers and oxygen from the pipes, giving about eight hours of active life to the inmates of the vessel when totally deprived of air externally.”
The store-rooms, mess-rooms, and quarters of the men were visited. Small though these rooms were, they were made with every convenience, and given every useful contrivance which this great age of invention could produce.
The Tracer was not a war vessel, but belonged to the Geographical Bureau, and was used in charting the Central Sea. Her complement was small: two engineers, two pilots, one electrician, cook, assistant cook, captain’s boy, two helpers, and two officers. Everything was so admirably arranged, and machinery played such a wonderful part in the power required to handle the vessel, that a larger force was not only unnecessary, but would have been detrimental to a satisfactory working of the vessel.
Cobb called attention to the steel partitions between the rooms, and asked why so much strength was required.
“There are,” answered Lieutenant Sibley, “twelve partitions, dividing the vessel into twenty-six compartments. In case of accident to the outer shell, whereby water might gain ingress, that particular compartment can instantly be closed and the flow of water confined to it. Before going down into the engine-room, I will give you some idea of this remarkable vessel. The Tracer, when fully submerged, displaces 1,000 tons of water. The shell of the vessel is of 1½-inch steel, covered externally by an aluminum armor of .3 of an inch in thickness, and weighs 570,000 pounds. The steel deck upon which we stand weighs 500,000; the steel partitions, braces, and iron-work weigh 195,000; the engines and machinery, 200,000; compressed air pipes, 125,000; the water cylinders, which you will soon see, weigh 100,000; all other parts, stores, lipthalite, etc., are allowed 50,000 pounds. Now, added to all this, is an immense aluminum-covered iron weight of 150,000 pounds attached to the bottom of the vessel, and which can instantly be freed and dropped from the ship into the sea, by simply breaking an electrical connection. This circuit is accessible from all parts of the vessel. Let us descend into the engine-rooms, and I will there explain why I have been so particular in giving you these weights.”
Following the Lieutenant down the narrow ladder into the depth below, Cobb, Rawolle, and Lyman were soon facing the powerful but small engines of the Tracer.
The room was large, clean, warm, and brightly illuminated by electricity. Here, Mr. Lochridge, the first engineer, was introduced by Lieutenant Sibley.