One of the vessels takes her station at the point of beginning the day's survey and anchors; the other vessel then comes sufficiently near to secure the end of the sweep line from the anchored ship and then moves over to her starting point, which might be only a few yards away or as much as a mile. I have found, in wreck-sweeping operations, that it is practical to go as much as a mile apart, depending upon how close together the contours are desired. These sweep lines of the two vessels are then joined together and the submarines sink to the bottom, on which they are allowed to rest with sufficient weight to prevent their being drifted out of their course.
We will assume that their starting points are one-half mile apart, and that they are to run contour lines due west from their respective starting points. The boats should therefore lie due north and south from each other, and the sweep lines should lead at right angles from each toward its companion boat. The dynamo is now started in the surface vessel to supply the motors in the submarines with power. The two submarines now start ahead.
The surface vessels, by means of their athwartship propellers, are always kept headed due west, therefore the course must also be due west. Each operator in the submarine keeps watch on his indicator, which records the amount of line paid out, and also enables him to be kept advised, by frequent inquiry through the telephone, of the amount of line his companion vessel has out. The operators also keep each other advised of the distance their respective vessels have travelled and the direction of lead of sweep line. Thus they can always keep each other on lines due north and south. If now an obstruction is struck, such as a rock, a sunken ship, etc., the strain on the sweep line becomes greater than normal, and the line commences to run off its drum. After running a short distance the sweep line will begin to lead aft instead of at right angles to the course. The two operators then stop and advise each other of the lead of the line. The one whose line leads the greater number of degrees off from right angles to the course is nearest the obstruction. He now turns his tractor wheel in the direction of the lead and wheels over to the obstruction, taking in his sweep lines as fast as he goes. The characteristics of the obstruction are noted, and its position accurately located by the triangulation method and recorded on the chart. In practice this sweep line extends a few feet above the bottom so as not to pick up small boulders, stones, etc., and would be caught only on the larger submerged objects. In taking off the readings from the contour sheets, when plotting the depths on the charts, the assurance can be had that no obstructions exist between the surface and the depth of the sweep line, as the depth and contour recording gauge is located at the height of the sweep line. The actual contour depth would be the distance between the sweep line and the water-bed, which could be added if desired.
As the submarine may be used for purposes of making navigation more safe, so also may it be used for the recovery of ships' cargoes and for salvaging ships which have had the misfortune to be sunk.
In searching for sunken vessels two boats are used, of the same general type as the "hydrographic submarine." When a wreck is located divers go out and examine it. If it is concluded that she has cargo on board worth salving, her location is plotted on the chart and then the recovery boats are sent out to remove the cargo. I have done much experimental work in locating sunken wrecks and recovering their cargoes. In 1898, 1899, and 1900 the Argonaut and special wreck-finding apparatus were used in this experimental work. Numerous wrecks were found and a number of cargoes were profitably recovered, notwithstanding the fact that the apparatus used was crude and experimental. In 1901 I was called from this line of work to take up the construction of submarine torpedo boats, and have been too busy ever since, building for the United States and foreign governments, to find the time and opportunity to push on this very interesting phase of submarine work.
THE "ARGONAUT" SUBMERGED
Drawn by C. McKnight Smith for Harper's Weekly, April 1, 1899. (By permission. Copyright 1899 by Harper & Brothers.) This shows the remodelled "Argonaut" with her buoyant ship-shaped superstructure, on a submerged wrecking expedition, as was actually accomplished in the years 1900-1901.
Searching for sunken vessels is, perhaps, the most interesting of all submarine work. It is like fishing. One is always on the qui vive for a "bite." There is hardly a location along our coast or in Long Island Sound that does not have a tradition about lost treasure ships, and every time one gets a "bite"—that is, our lines get fast to some sunken object—excitement runs high in the expectation of some valuable find. In my experimental work in the vicinity of Bridgeport, Connecticut, we located sixteen sunken vessels, the great majority of them containing coal, which we recovered at a cost of about fifty cents per ton. Most of these vessels had been sunk a long time. Only a few of them were known by name, and some had evidently been sunk many years. One that we searched for during several months had a cargo of copper ore and copper matté which was quite valuable. We finally found her several miles away from where people testified they saw her disappear.
Somewhere off Bridgeport lies the wreck of the old Sound steamer Lexington. Legend has it that she has a fortune in her safe. Many a ship has been sunken in the waters about Hell Gate; search was carried on there for years for the old British frigate Hussar, which struck on Pot Rock and sank during the Revolutionary War. Tradition has it that she had four million dollars (£820,000) in gold on board to pay off the British troops, and that she carried this treasure to the bottom with her. There is a cargo of block tin somewhere in a sunken barge off the Battery, and many a ship with valuable cargoes lies along the coast from Newfoundland to Key West. The yearly loss in ships and cargoes throughout the world has always run into many millions of dollars, and since the war this has been multiplied a hundred-fold, and amounts to billions. The time will come when many of these ships will be found, and such of their cargo as is still valuable will be salvaged. Salving a sunken cargo is not a difficult engineering feat, providing the proper apparatus is at hand. It is the novelty of the enterprise and the mystery surrounding submarine work that make it so difficult to the layman. Diving, as heretofore conducted, has been difficult and dangerous work, and only the strong could stand the hardships connected with it. The advent of submarine salvage vessels fitted with proper machinery and in the application of scientific methods, however, will clear away many of the hardships and dangers connected with salving a sunken cargo, and more experience and proper apparatus will prove that certain cargoes may be removed from sunken ships in moderate depth with almost as much rapidity as they can be lifted from the hold of a vessel alongside of a dock. Take anthracite coal, for instance. With a six-inch pump, on the old Argonaut, I have transferred fifteen tons of nut coal from a sunken barge to a sunken freight-carrying submarine in nine minutes. A turn of the air valve then sent the sunken freight boat to the surface. The coal was transferred while all the boats were submerged in seven fathoms of water. It was this kind of experimental work which has enabled me to devise apparatus which will undoubtedly operate successfully on a much larger scale, as explained in the illustrations.