The method of charting our coast lines and the estuaries of the sea has been by the use of the sounding lead, taken at points a greater or less distance apart. The depths recorded at these points are plotted by the triangulation method of location from tripods or known structures, or objects on shore, and shown on the chart. These points would need to be taken every few feet to give an accurate topography of the bottom, the cost of which, in time and money, would be prohibitive. Assuming that our coast waters were sounded and depths recorded, at points only fifty feet apart in all directions, even such close soundings would not guarantee that some peak might not project above the bottom and prove disastrous to some ship.
I remember some few years ago the battleship Missouri struck such a peak in New York Harbor, seriously injuring her bottom. Thousands of ships of equal draft had passed this vicinity, but none of them had happened to strike this particular spot and no one suspected that such a rock existed in this much-frequented highway. In 1900 the steamer Rio de Janeiro struck an unknown rock in entering the harbor of San Francisco, with a loss of one hundred and thirty-one lives and over two million dollars in property.
In Long Island Sound we found, during a deep submergence trial with one of our submarines, a depth of two hundred and fifty-six feet, whereas the chart indicated a depth of only twenty-seven fathoms (one hundred and sixty-two feet).
In one instance in Russia we were conducting submerged trials on the official trial course of the Russian Government in the Gulf of Finland, this being the course on which they tried their surface torpedo boats, and we were assured that there was not less than sixty feet of water on the course, yet we struck rock peaks twice on this course in less than thirty feet depth. The record of ships that have been lost, due to striking uncharted rocks and shoals, is a large one, and a more correct topography of the water-beds of our coast and inland waterways should be worked out. In 1899 and 1901 considerable time was spent in experimental work with the submarine boat Argonaut in locating sunken ships and recovering their cargoes. To find a sunken ship it was necessary to search the bottom thoroughly, and many experiments were made and success attained to such an extent that we could search thoroughly an under-water area of from ten to twenty square miles per day. It is the result of this experimental work that has led to the design of the herein-described apparatus, which will give very accurate contour records of the bottom within such depths as would prove of interest to navigators of either surface vessels or submarines. The advent of the submarine has made it more important to know where obstructions exist, as they require at least seventy feet depth to navigate at speed entirely submerged and to enable them to keep below the bottom of surface ships. This method of water-bed surveying consists of using two or more submarine boats of my bottom-navigating type, with access tubes extending to surface vessels. Instead of using two bottom wheels arranged in tandem, as is used on my military submarine, I use a single pair of toothed driving wheels capable of being swivelled and driven to propel the submarine in any desired direction over the bottom. The submarine vessel contains also a diver's compartment, so that examinations of the bottom may be made and a record kept of the materials and conditions found, which are recorded as frequently as may be desired directly on the contour sheet, on which the soundings are being automatically recorded.
Navigators of surface vessels are interested principally in knowing the amount of water they have beneath their keel and the nature of the bottom, so that they may judge of their location by soundings, especially in time of fog. It is not essential, therefore, to know every foot of the bottom, but it is essential to know that no obstructions exist extending nearer to the surface than their keel. It is also essential for submarine commanders to know that there are no obstructions nearer the surface than their depth of submergence, if they are running submerged at speed. It is possible that collisions with submerged obstructions may have been responsible for some of the mysterious submarine fatalities.
This method of bottom investigation permits of very accurate contour lines being run as close together as may be desired for harbor work. On the coast, in depths exceeding fifty to seventy-five feet, if contours were run one-half mile apart, it would probably be satisfactory if a guaranty could be given that there were no obstructions over five or six feet in height which lay between such contours. Two vessels as herein described are capable of automatically recording parallel contours at the rate of two or three miles per hour and to guarantee that there are no dangerous obstructions lying between them.
Referring to [page 267], a surface vessel is shown with a well which extends from under the pilot-house and out under her stem. An access tube extends from this well forward to a small submarine vessel. The upper end of this access tube is pivoted to strong bearings secured in the sides of the well, and is further secured by tension rods extending from part way down the tube to bearings secured to the outer skin of the ship in line with the bearings in the well. Large bearings with stuffing boxes in the submarine boat end of the access tube permit of access through a door to an air-lock compartment, and a second door leads from the air-lock into the diving compartment, a sliding door in the bottom of the diving compartment permitting the door to be opened for inspection of the bottom. By donning a diving suit members of the crew may also leave or enter the vessel when on the bottom. The water is kept from entering the diving compartment by air compressed to the same pressure as the surrounding water pressure, corresponding to the depth of submergence, the same as is done in my military submarine boats. A motor, drawing its power from a dynamo on the surface vessel, drives through suitable gearing the tractor wheel arranged near the bow of the submarine. This tractor wheel may be turned by its vertical steering post so as to propel the vessel in any desired direction.
The weight of the submarine upon the bottom is regulated by water ballast. A depth-recording device operates in connection with a distance-recording apparatus, so that an exact contour of the bottom is reproduced on a roll of paper, the record being made by the revolution of the tractor wheels. Corrections of errors are made by taking observations from the surface vessels from known points on shore by the usual triangulation method.
A drum is mounted on the submarine on which is wound a double wire. The upper wire is an insulated wire and is used to telephone between the two submarine vessels. The lower wire is a bare wire and is used to locate obstructions. The two wires are secured together as shown. Suitable recording devices in the interior of each vessel give the amount of wire unwound from its drum. A tension regulator holds a certain desired strain or pull upon the sweep lines, and another indicator gives the direction of lead of the wires during the "sweeping" operations. The surface vessel has a propeller in her skeg operating athwartship in addition to the usual stem propeller.
The method of operation is as follows: Two vessels are required, which proceed to the location to be charted. In surface navigation the submarine, carried at the forward end of the access tube, is emptied of her water ballast and floats on the surface in front of the surface vessel, being pushed ahead of the latter vessel by the access tube, the pivoted bearings at each end of the tube giving sufficient flexibility to prevent any damage to the tube because of strains set up by the waves.