LEAK ARRESTERS FOR SHIPS.
Experiments made by Mr. Colomes, a French inventor, with cellulose applied to holes in the hull, induced the French Government to adopt his device to be used on board its war vessels.
The apparatus for applying the cellulose to the hole is extremely simple. It is composed of a steel rod, threaded on a part of its length, at the end of which is pivoted an iron piece, which, when at right angles to the rod, has the appearance of a pickaxe, one of the arms of this cross piece being heavier than the other. This cross piece has fixed to it an oval piece of flat iron covered on both sides with thick felt. A small conical bag, filled with cellulose and having a hole through its center, can be slid on to the rod. Back of this bag is applied a large washer, which is held in place against the bag by a nut which is pushed down the rod to the threaded part, where it engages the screw. When a leak has been located any man can seize a leak stopper corresponding approximately in size to the width of the hole. Then holding it with the lighter end of the pick toward him, so that the pick and oval plate lie alongside the rod, he can introduce it into the hole. He can avoid the rush of the water by standing to one side. As soon as the pick has passed through the plating the heavier end descends and the pick places itself across the hole while the pressure of the outside water forces it against the side of the vessel and throws the pick arm across the opening, so, resting on the plating around the hole, it affords a point of support, while the felt covered plate reduces the leak very much and makes easier the next operation, which consists in slipping the bag of cellulose, washer and nut over the rod, screwing down the nut till the bag of cellulose is compressed against the hole. The cellulose bag fills up all parts of the hole, no matter how irregular, as the great value of the cellulose consists in its absorbing water and greatly increasing its volume. This elastic mass makes a tightly applied mat over the hole, which cannot be accidentally disturbed or displaced. Should the hole not be more than to inches wide and several feet long, a number of leak stoppers can be used side by side so as to gradually fill the hole.
Three sizes of arresters are used: No. 1 for holes from 1 ½ to 3 inches, No. 2 for holes from 3 to 6 inches and No 3 for holes from 6 to 10 inches.
In order to practically demonstrate the value of the leak arrester, the Franco-American Cellulose Company of 831 Arch street, Philadelphia, erected at their works a set of tanks pierced with holes of different sizes and shapes. The first experiment took place last year before a board appointed by the Navy Department and a number of naval officers and naval constructors, among whom were Lewis Nixon, chief constructor of the William Cramp & Sons Ship and Engine Building Company, and Captain Constance, naval attaché of the British Legation in Washington. The leak arresters were to be placed in three holes cut in the sides of an iron tank. The smallest hole was circular with burred edges and was 2 ½ inches in diameter; the next was hexagonal, about 10 inches wide, its area being about 72 square inches; the third was very irregular in shape and about 2 ½ inches long, the average width being about 5 inches and the area 85 square inches. It being understood that the stoppers are intended to be used from .the inside of the ship, the tanks were supposed to represent the sea and the holes or rents were located at a depth of 10 or 12 feet below the water line, with a corresponding water pressure. The tanks were kept full by means of a pump so as to preserve the same head of water during all the tests.
The time employed to effectually close the holes under a head of water of 12 feet was as follows:
1. 2 ½-inch hole 30 seconds.
2. 10-inch hole . 1 minute.
3. 21-inch hole 3 minutes.
Another test made immediately after the above, using a water pressure of 9 feet, gave the following results:
10-inch hole 37 seconds.
21-inch hole 1 minute, 40 seconds.
During the latest tests made three leak stoppers were placed side by side, instead of two, in order to show that any number of leak stoppers can be employed to gradually decrease the leakage until the hole is under control. It is said that after the test Constructor Nixon expressed his opinion as follows:
"The experiment was a signal success, and the holes were stopped in remarkably short periods. By the use of the Colomes leak stoppers and cellulose any leak in any vessel can be stopped before an appreciable quantity of water can rush in."
For holes of much larger area Mr. Colomes proposes to use a cellulose mat to be applied from the outside of the vessel. This mat resembles an ordinary mattress, filled with obturating cellulose and is made in several sizes. The side of the mat away from the side next to the ship is covered with water proof cloth in order to prevent too much water from filtering through the cellulose. On the sides and at the corners rings are fixed intended to receive guiding ropes. Such ropes should always be kept in readiness on the upper deck, bent and with the slack so arranged that they will fall under the vessel so as to hang from gunwale to gunwale. These ropes are to receive the mats as soon as a leak is discovered and located. The soft pliant nature of the cellulose lining of the mat enables the pressure of the water to force it into all parts of the opening, so that every crack is filled and the inflow automatically stopped.
The Franco-American Cellulose Company is now experimenting with a view to finding- a non-combustible substitute for the woodwork of the cruisers and battle-ships of the navy.
EXPERIMENTS ON WIND PRESSURE.
The subject of wind pressure is one on which our knowledge at the present day is not only limited, but exceedingly vague, and carefully-made experiments, if but to investigate a single feature of the problem, are, therefore, of the greatest interest, and can hardly fail to add something new to our information. Mr. J. Irminger, C. E., Member of the Danish Society of Engineers, has determined, what it is believed no one before him has attempted to do, the amount of suction produced by a current of air striking a plane surface, or the surfaces of various bodies; and the results of his experiments form the subject of a paper with the above title, read before that society in the early part of last summer. These results are remarkable in showing how very large a percentage of the total effect this suction is, not only through its action on the leeward side, but on the windward as well. In fact, when the angle at which the wind strikes a plane surface is small, nothing but suction is produced.
The practical importance of these experiments are evident; they throw considerable light on the subject of flight, which at present is engaging so much attention; and in structural designing they point out the way to more rational methods. We have hitherto considered the resultant of the pressure only, but if that of the suction is also taken into account, the final resultant is changed both in amount and direction. Thus in the case of a roof, given below, the resultant of suction and pressure will tend to lift, and not overturn it, which is in accordance with experience.
Experiments on wind pressure have usually been made by causing the body subject to the pressure to revolve in still air. The author's experiments were made with a fixed body exposed to a current of air. This current was obtained by making an opening into a large chimney 100 feet in height and fitting to this opening a rectangular, horizontal wooden tube, g inches by 4 inches in section, internally polished. The experiments were directed to ascertain the distribution of pressure over the surfaces both of planes (i. e., solids of small thickness) and of bodies of various forms. Taking first the case of planes, the plane was represented in the experiments by two pieces of sheet iron, 4 inches by 1 ½ inch, placed 1/16 inch apart, and connected together along their edges so as to form a shallow, closed box. To the interior of this box a pressure gauge was connected by means of a small pipe. A number of small holes were made in both faces of the box of which one at a time was opened. . By this means, the pressure gauge registered the pressure at any desired point in the windward or leeward side of the box. The pressure-pipe formed an axle on which the box could be turned to any desired angle with the wind. By means of a valve in the wooden tube the velocity could be varied. The velocities employed were from 25 feet to 50 feet per second. Besides the plane above described, which occupied the full width of the tube, (and may therefore be considered to represent in the open air a plane whose width is very great in proportion to its length measured in the direction of the wind), another plane was experimented with, measuring only 2 ½ inches by 1 ½ inch. It should be remarked that the velocity of the wind was obtained from the observed normal pressures by reference to the ordinary tables. In the following tables based on the experiments, it should be especially noted that at small angles of incidence the effect of rarefaction on the leeward side (showing itself as suction) causes practically all the pressure on the plane, and that at so small an angle as 50 this suction is over 1 of the total pressure (that caused by the wind direct, plus that caused by suction) on the same plane placed normally.
The total pressures agree fairly well with those of Professor Langley given in the Proceedings of the Royal Society for 1889. The variations are readily accounted for by the change in form, which has considerable effect, even with plane surfaces.
Doubtless in connection with the observed results at small angles of incidence, many readers will call to mind cases where, with a light beam wind and yards nearly square, a vessel under sail alone has made some phenomenal speed, unaccounted for except on the supposition that the real direction of the wind was from a point abaft its apparent direction. This, however, is no explanation at all, as will be seen by a little consideration. What is meant by the real direction of the wind, is only relative; it is the direction with regard to a fixed point on the earth's surface. The apparent direction of the wind is a resultant of two motions, and is the true direction with regard to i moving object on the earth's surface, namely, the ship. There is no more reason to take into consideration the direction of the wind with regard to a fixed point on the earth's surface, than with regard to a fixed point in space, and this latter is manifestly absurd. But much of the result of trimming yards fine for winds abeam is readily accounted for by the suction.
Probably the high speed of the ice boat is largely due to the same thing. The same is true of wind-mills.
It is observed that the bird holds its wing at an angle of 60 with the horizon; at this inclination the effect of the wind upon the under side of the surface is zero, while the suction acting on the upper side is equivalent to an upward pressure which sustains the bird. Moreover, the friction of the medium through which the bird moves is hereby reduced, and a current is produced acting towards the wing, and inclined upward at a small angle.
The method used with these bodies is similar to that described for plane surfaces; the different bodies are hollow and made of thin sheet iron ; they are about 4 in. long, and provided with three holes in a row in the middle of one side. A hollow axis passes through the center, and communication is made with the pressure gauge in the same manner as before.
In the case of the cylinder, which was examined by boring a single hole in it and revolving it gradually through 360°, it was found that pressure existed only between 0° and 35°, when the effect became a suction. Similar results were found for the sphere.
Models were also experimented with representing buildings with roofs of various forms, and diagrams are given showing the distribution of pressure over leeward and windward sides. In all cases rarefaction on the side is quite as important a factor in the actual resultant force on the building as is the positive pressure on the windward side. The case of the pitched roof making angles of 450 with the horizontal on which a horizontal wind acts at right angles to the ridge is particularly worthy of note, and furnishes some food for thought. The normal pressure on the lee side due to suction is more than three times as great as that on the weather side. The resultant pressure on the two faces [neglecting the walls of the building] is inclined upwards and is about three and one half times as great as that on the weather side. On the weather side, the pressure is greatest near the lower edge, diminishes uniformly and becomes a suction near the ridge.
A REDUCIBLE LIFE-BUOY, AND THE GALIBERT RESPIRATORY APPARATUS.
Up to the present time solid bodies have commonly been used for rafts. Now the fact is, that the specific weight of the lightest of these rafts or floats is not much less than that of water, thus making it necessary to give them a great volume in order to obtain an indifferent floating capacity. M. Galibert has put them aside in constructing his buoy, which he has made of a special fabric perfectly water-tight and impermeable to water for several consecutive days. This reducible life-buoy has, when folded, a very small volume and an insignificant weight. It is easily inflated, and an air cushion is obtained, to which sailors have given the characteristic name of "turtle," owing to its shape and dimensions. The so-called personal buoy is so light, and presents such a small volume, that it may be kept in a small valise when the air is let out. Large buoys which have one thousand pounds resistance to submersion are so arranged that they can be immediately turned into a large raft, and be very useful in case of sudden shipwreck, taking the place of boats, which are often smashed in the breakers on landing, or which cannot be lowered owing to the position of the ship.
Another contrivance very useful in the equipment of a vessel is the "respiratory apparatus," which consists essentially of an impermeable bag constructed on the principle of the reducible buoy, and which contains a sufficient supply of air to permit the saving of life in an asphyxiating locality. This pure air reservoir fixed upon the back so as to permit of free motion, and having a tube connecting with the mouth, with a nose compresser or pince-nez, allows a person to breathe normally without taking in any of the vitiated atmosphere by which he is momentarily surrounded. Suppose, for instance, a case of fire on board the ship; the smoke reveals the locality of the fire, but prevents getting at its origin, and putting it out in the beginning. Provided, however, with the above apparatus, any one among the crew can go down in the hold, and thus arrest the progress of the conflagration. The same would be true in case of foul gases developing in coal bunkers or any other part of the ship. Both apparatus have been successfully tested, and have received the official sanction of the (French) Government. J. L.