THE TRANSMISSION OF POWER ON A SHIP
There are four power agents available on board ship, all derived directly or indirectly from the steam boilers. They are:—
(1) Steam.
(2) High-pressure water.
(3) Compressed air.
(4) Electricity.
On some ships we may find all four working side by side to drive the multifarious auxiliaries, since each has its peculiar advantages and disadvantages. At the same time, marine engineers prefer to reduce the number as far as possible, since each class of transmission needs specially trained mechanics, and introduces its special complications.
Let us take the four agents in order and briefly consider their value.
Steam is so largely used in all departments of engineering that its working is better understood by the bulk of average mechanics than hydraulic power, compressed air, or electricity. But for marine work it has very serious drawbacks, especially on a war vessel. Imagine a ship which contains a network of steam-pipes running from end to end, and from side to side. The pipes must, on account of the many obstacles they encounter, twist and turn about in a manner which might be avoided on land, where room is more available. Every bend means friction and loss of power. Again, the condensation of steam in long pipes is notorious. Even if they are well jacketed, a great deal of heat will radiate from the ducts into the below-deck atmosphere, which is generally too close and hot to be pleasant without any such further warming. So that, while power is lost, discomfort increases, with a decided lowering of human efficiency. We must not forget, either, the risk attending the presence of a steam-pipe. Were it broken, by accident or in a naval engagement, a great loss of life might result, or, at least, the abandonment of all neighbouring machinery.
For these reasons there is, therefore, a tendency to abolish the direct use of steam in the auxiliary machinery of a modern vessel.
High-pressure water is free from heating and danger troubles, and consequently is used for much heavy work, such as training guns, raising ashes and ammunition, and steering. One of its great advantages is its inelasticity, which prevents the overrunning of gear worked by it. Water, being incompressible, gives a "positive" drive; thus, if the pump delivers a pint at each stroke in the engine-room a pint must pass into the motor, assuming that all joints are tight, and the work due from the passage of one pint is done. Air and steam—and electricity too, if not very delicately controlled—are apt to work in fits and starts when operating against varying resistance, and "run away" from the engineer.
An objection to hydraulic power is, that all leakage from the system must be replaced by fresh water manufactured on board, which, as we have seen, is no easy task.
Compressed air, like steam, may cause explosions; but when it escapes in small quantities only it has a beneficial effect in cooling and freshening the air below decks. The exhaust from an air-driven motor is welcome for the same reason, that it aids ventilation. On a fighting ship it is of the utmost importance that the personnel should be in good physical condition; and when the battle-hatches have been battened down for an engagement any supply of fresh oxygen means an increased "staying power" for officers and crew. Poisoned air brings mental slackness, and weakening of resolve; so that if the motive power of heavy machinery can be made to do a second duty, so much the better for all concerned.
Compressed air also proves useful as a water-excluder. If a vessel contain, as it should, a number of water-tight compartments, any water rushing into one of these can be expelled by injecting air until the pressure inside is equal to that of the draught of water of the vessel outside.
On land compressed-air installations include reservoirs of large size in which air can be stored till needed, and which take the place of the accumulator used with hydraulic power. On shipboard want of space reduces such reservoirs to minimum dimensions, so that the compressors must squirt their air almost directly into the cylinders which do the work. When the load, or work, is constantly varying, this direct drive proves somewhat of a nuisance, since the compressors, if worked continuously at their maximum capacity, must waste large quantities of air, while if run spasmodically, as occasion demands, they require much more attention. It is therefore considered advisable by some marine engineers to make compressed air perform as many functions as possible when it is present on a vessel. The United States monitor Terror is an instance of a warship which depends on this agency for working her guns and turrets, handling ammunition, and—a somewhat unusual practice—controlling the helm. The last operation is performed by two large cylinders placed face to face athwart the ship. They have a common piston-rod, in the middle of which is a slot for the tiller to pass through. Air is admitted to the cylinders by a valve which is controlled by wires passing over a train of wheels from different stations on the ship. An ingenious device automatically prevents the tiller from moving over too fast, and also helps to lessen the shocks given to the rudder by a heavy sea.
We now come to electricity, the fourth and most modern form of transmission. Its chief recommendation is that the wires through which it flows lend themselves readily to a tortuous course without in any way throttling the passage of power. And as every ship must carry a generating plant for lighting purposes, the same staff will serve to tend a second plant for auxiliary machinery. Electric motors work with practically no vibration, are light for their power, and can be very easily controlled from a distance. They therefore enjoy increasing favour; and are found in deck-winches, anchor-capstans, ammunition hoists, ventilation blowers, and cranes. They also control the movements of gun-turrets, having been found most suitable for this work.
If the current were to get loose in a ship it would undoubtedly cause more damage than an escape of compressed air or water. Electricity, even when every known means of keeping it within bounds has been tried, is suspected of causing deterioration to the metalwork of ships. But these disadvantages are not serious enough to hamper the progress of electrical science as applied to marine engineering; and the undoubted economy of the electric motor, its noiselessness, its manageableness, and comparatively small size will, no doubt, in the future lead to its much more extensive use on board our floating palaces and floating forts.
FOOTNOTES:
[16.] F. M. Bennett, in the Journal of the American Society of Naval Engineers.
[17.] Charles V. Daly, in The Magazine of Commerce.
[CHAPTER XIII]
"THE NURSE OF THE NAVY"
Just as a navy requires floating distilleries, floating coal stores and floating docks, so does it find very important uses for a floating workshop, which can accompany a fleet to sea and execute such repairs as might otherwise entail the return of a ship to port.
The British Navy has a valuable ally of this kind in the torpedo depôt ship Vulcan, which contains so much machinery, in addition to the "auxiliaries" already described, that a short account of this vessel will be interesting.
The Vulcan, known as "The Nurse of the Navy," was launched in 1889. She measures 350 feet in length, 58 feet in beam, and has a displacement of 6,830 tons. Her bunkers, of which there are twenty-one, hold 1,000 tons of coal, independently of an extra 300 tons which can be stowed in other neighbouring compartments. When fully coaled she can cruise for 7,000 miles at a speed of 10 knots; or travel at first-class cruiser speed for shorter distances.
The most striking objects on the Vulcan are two huge hydraulic cranes, placed almost amidships abreast of one another. They have a total height of 65 feet, and "overhang" 35 feet, so as to be able to lift boats when the torpedo-nets are out and the sides of the vessel cannot be approached. The feet of the cranes sink 30 feet through the ship to secure rigidity, and the upper deck, which bears most of the strain, is strongly reinforced. Inside the pillar of each crane is the lifting machinery, an hydraulic ram 17 1 / 2 inches in diameter and of 10-foot stroke. By means of fourfold pulleys the lift is increased to 40 feet. When working under the full pressure of 1,000 lbs. to the square inch, the cranes have a hoisting power of twenty tons. In addition to the main ram there is a much smaller one, the function of which is to keep the "slings" (or cables by which the boat is hoisted) taut after a boat has been hooked until the actual moment of lifting comes. But for this arrangement there would be a danger of the slings slackening as the boat rises and falls in a seaway. The small ram controls the larger, and the latter cannot come into action until its auxiliary has tightened up the slings, so that no dangerous jerk can occur when the hoisting begins.
The cranes are revolved by two sets of hydraulic rams, which operate chains passing round drums at the feet of the cranes, and turn them through three-quarters of a circle.
On the Vulcan's deck lie six torpedo boats and three despatch boats. The former are 60 feet long, and can attain a speed of 16 knots an hour. When an enemy is sighted these would be sent off to worry the hostile vessels with their deadly torpedoes, and on their return would be quickly picked up and restored to their berths, ready for further use.
The cranes also serve to lift on board heavy pieces of machinery from other vessels for repair.
Photo Cribb.
A 12-inch gun being lowered into its place in the turret of a warship by a gigantic sheer-leg crane, one leg of which is partly visible on the left of the picture.
Down below decks is the workshop, wherein "jobs" are done on the high seas. It has quite a respectable equipment: five lathes, ranging from 15 feet to 3 1 / 2 feet in length; drilling, planing, slotting, shaping, punching machines; a carpenter's bench; fitters' benches; and a furnace for melting steel. There is also a blacksmith's shop with an hydraulic forging press and a forge blown by machinery; not to mention a large array of tools of all kinds. Special engines are installed to operate the repairs department.
The Vulcan also carries search-lights of 25,000 candle-power; bilge pumps which will deliver over 5,000 tons of water per hour; two sets of engines for supplying the hydraulic machinery; air-compressing engines to feed the Whitehead torpedoes; a distilling plant; and last, but by no means least, main engines of 12,000 h.p. drawing steam from four huge cylindrical boilers 17 feet long and 14 feet in diameter.
Altogether, the Vulcan is a very complete floating workshop, sufficiently speedy to keep up with a fleet, and even to do scouting work. Her guns and her torpedo craft would render her a very troublesome customer in a fight, though, being practically unarmoured, she would keep as clear of the conflict as possible, acting on the offensive through the proxy of her "hornets." She constitutes the first of a type of vessel which has been suggested by experts, viz. one of high speed and unarmoured, but capable of carrying a swarm of torpedo boats which could be launched in pursuit of the foe. Even if 50 per cent. of the craft were destroyed, the price would be small if a single torpedo were successfully fired at a battleship. The naval motor boat, to which reference has already been made, would just "fill the bill" for such a cruiser; and in the event of a score of them being dropped into the water at a critical moment, they might easily turn the scale in favour of their side.
[CHAPTER XIV]
THE MECHANISM OF DIVING
Diving being a profession which can be carried on in its simplest form with the simplest possible apparatus—merely a rope and a stone—its history reaches back into the dim and inexplorable past. We may well believe that the first man who explored the depths of the sea for treasure lived as long ago as the first seeker for minerals in the bosom of the earth. Even when we come to the various appliances which have been gradually developed in the course of centuries, our records are very imperfect. Alexander the Great is said to have descended in a machine which kept him dry, while he sought for fresh worlds to conquer below the waves. Aristotle mentions a device enabling men to remain some time under water. This is all the information, and a very meagre total, too, that we get from classical times.
Stepping across 1,500 years we reach the thirteenth century, about the middle of which Roger Bacon is said to have invented the diving-bell. But like some other discoveries attributed to that Middle-Age physicist, the authenticity of this rests on very slender foundations. In a book published early in the sixteenth century there appears an illustration of a diver wearing a cap or helmet, to which is attached a leather tube floated on the surface of the water by an inflated bag. This is evidently the diving dress in its crudest form; and when we read how, in 1538, two Greeks made a submarine trip under a huge inverted chamber, which kept them dry, in the presence of the great Emperor Charles V. and some 12,000 spectators, we recognise the diving-bell, now so well known.
The latter device did not reach a really practical form till 1717, when Dr. Halley, a member of the Royal Society, built a bell of wood lined with lead. The divers were supplied with air by having casks-full lowered to them as required. To quote his own words: "To supply air to this bell under water, I caused a couple of barrels of about thirty gallons each to be cased with lead, so as to sink empty, each of them having a bunghole in its lowest parts to let in the water, as the air in them condensed on their descent, and to let it out again when they were drawn up full from below. And to a hole in the uppermost parts of these barrels I fixed a leathern hose, long enough to fall below the bunghole, being kept down by a weight appended, so that the air in the upper parts of the barrels could not escape, unless the lower ends of these hose were first lifted up. The air-barrels being thus prepared, I fitted them with tackle proper to make them rise and fall alternately, after the manner of two buckets in a well; and in their descent they were directed by lines fastened to the under edge of the bell, which passed through rings on both sides of the leathern hose in each barrel, so that, sliding down by these lines, they came readily to the hand of a man, who stood on purpose to receive them, and to take up the ends of the hose into the bell. Through these hose, as soon as their ends came above the surface of the water in the barrels, all the air that was included in the upper parts of them was blown with great force into the bell, whilst the water entered at the bungholes below and filled them, and as soon as the air of one barrel had been thus received, upon a signal given that was drawn up, and at the same time the other descended, and by an alternate succession, provided air so quick and in such plenty that I myself have been one of five who have been together at the bottom, in nine to ten fathoms water, for above an hour and a half at a time, without any sort of ill-consequence, and I might have continued there so long as I pleased for anything that appeared to the contrary." After referring to the fact that, when the sea was clear and the sun shining, he could see to read or write in the submerged bell, thanks to a glass window in it, the Doctor goes on to say: "This I take to be an invention applicable to various uses, such as fishing for pearls, diving for coral or sponges and the like, in far greater depths than has hitherto been thought possible; also for the fitting and placing of the foundations of moles, bridges, etc., in rocky bottoms, and for cleaning and scrubbing ships' bottoms when foul, in calm weather at sea. I shall only intimate that, by an additional contrivance, I have found it not impracticable for a diver to go out of an engine to a good distance from it, the air being conveyed to him with a continued stream by small flexible pipes, which pipes may serve as a clue to direct him back again when he would return to the bell."
We have italicised certain words to draw attention to the fact that Dr. Halley had invented not only the diving bell, but also the diving dress. Though he foresaw practically all the uses to which diving mechanism could be put, the absence of a means for forcing air under pressure into the bell or dress greatly limited the utility of his contrivances, since the deeper they sank below the water the further would the latter rise inside them. It was left for John Smeaton, of Eddystone Lighthouse fame, to introduce the air-pump as an auxiliary, which, by making the pressure of the air inside the bell equal to that of the water outside, kept the bell quite free of water. Smeaton replaced Halley's tub by a square, solid cast-iron box, 50 cwt. in weight, large enough to accommodate two men at a time. The modern bell is merely an enlarged edition of this type, furnished with telephones, electric lamps, and, in some cases, with a special air-lock, into which the men may pass when the bell is raised. The pressure in the air-lock is very gradually decreased after the bell has reached the surface, if work has been conducted at great depths, so that the evil effects sometimes attending a sudden change of pressure on the body may be avoided.
Diving bells are very useful for laying submarine masonry, usually consisting of huge stone blocks set in hydraulic cement. Helmet divers explore and prepare the surface on which the blocks are to be placed. Then the bell, slung either from a crane on the masonry already built above water-level, or from a specially fitted barge, comes into action. The block is lowered by its own crane on to the bottom. The bell descends upon it and the crew seize it with tackle suspended inside the bell. Instructions are sent up as to the direction in which the bell should be moved with its burden, and as soon as the exact spot has been reached the signal for lowering is given, and the stone settles on to the cement laid ready for it.
The modern diver is not sent out from a bell, but has his separate and independent apparatus. The first practical diving helmet was that of Kleingert, a German. This enclosed the diver as far as the waist, and constituted a small diving bell, since the bottom was open for the escape of vitiated air. Twenty years later, or just a century after the invention of Halley's bell, Augustus Siebe, the founder of the present great London firm of Siebe, Gorman, and Company, produced a more convenient "open" dress, consisting of a copper helmet and shoulder-plate in one piece, attached to a waterproof jacket reaching to the hips.
The disadvantage of the open dress was, that the diver had to maintain an almost upright position, or the water would have invaded his helmet. Mr. Siebe therefore added a necessary improvement, and extended the dress to the feet, giving his diver a "close" protection from the water.
We may pass over the gradual development of the "close" dress and glance at the most up-to-date equipment in which the "toilers of the deep" explore the bed of Old Ocean.
The dress—legging, body, and sleeves—is all in one piece, with a large-enough opening at the shoulders for the body to pass through. The helmet, with front and side windows, is attached by a "bayonet joint" to the shoulder-plate, itself made fast to the upper edge of the dress by screws which press a metal ring against the lower edge of the plate so as to pinch the edge of the dress.
Photo Cribb.
THE DIVER AT WORK
Note the telephone attachment, the wires of which are embedded in the life-line held by the bluejacket on the left. By means of the telephone the diver can give and receive full instructions about his work.
At the back are an inlet and an outlet valve. Between the front and a side window is the transmitter of a loud-sounding telephone, and in the crown the receiver and the button of an electric bell. The telephone wires, and also the wires for a powerful electric light, working on a ball-and-socket joint in front of the dress, are embedded into the life-line. The air-tube, of canvas and rubber, has a stiffening of wire to prevent its being throttled on coming into contact with any object. A pair of weighted boots, each scaling 17 lbs., two 40-lb. lead weights slung over the shoulder, and a knife worn at the waist-belt, complete the outfit of the diver, which, not including the several layers of underclothing necessary to exclude the cold found at great depths, totals nearly 140 lbs. Of this the copper helmet accounts for 36 lbs.
On the surface are the air-pumps, which may be of several types—single-cylinder, double-acting; double-cylinder, double-acting; or three or four cylinder, single-acting—according to the nature of the work. All patterns are so constructed that the valves may be easily removed and examined.
The pressure on a diver increases in the ratio of about 4 1 / 4 lbs. for every ten feet he descends below the surface. A novice experiences severe pains in the ears and eyes at a few fathoms' depth, which, however, pass off when the pressures both inside and outside of the various organs have become equalised. On rising to the surface again the pains recur, since the external pressure on the body falls more quickly than the internal. The rule for all divers, therefore, is "slow down, slow up." Men of good constitution and resourcefulness are needed for the profession of diving. Only a few can work at extreme depths, though an old hand is able to remain for several hours at a time in sixty feet of water. The record depth reached by a diver is claimed by James Hooper, who, when removing the cargo of the Cape Horn, wrecked off the coast of South America, made seven descents to 201 feet, one of which lasted forty-two minutes.
In spite of the dangers and inconveniences attached to his calling, the diver finds in it compensations, and even fascinations, which outweigh its disadvantages. The pay is good—£1 to £2 a day—and in deep-sea salvage he often gets a substantial percentage of all the treasure recovered, the percentage rising as the depth increases. Thus the diver Alexander Lambert, who performed some plucky feats during the driving of the Severn Tunnel,[18] received £4,000 for the recovery of £70,000 worth of gold from the Alphonso XII., sunk off Grand Canary. Divers Ridyard and Penk recovered £50,000 from the Hamilla Mitchell, which lay in 160 feet of water off Shanghai, after nearly being captured by Chinese pirates; and we could add many other instances in which treasure has been rescued from the maw of the sea.
The most useful sphere for a diver is undoubtedly connected with the harbour work and the cleaning of ships' bottoms. For the latter purpose every large warship in the British Navy carries at least one diver. After ships have been long in the water barnacles and marine growths accumulate on the below-water plates in such quantities as to seriously diminish the ship's speed, which means a great waste of fuel, and would entail a loss of efficiency in case of war breaking out. Armed with the proper tools, a gang of divers will soon clean the "foul bottom," at a much smaller cost of time and money than would be incurred by dry-docking the vessel.
The Navy has at Portsmouth, Sheerness, and Devonport schools where diving is taught to picked men, the depth in which they work being gradually increased to 120 feet. Messrs. Siebe and Gorman employ hundreds of divers in all parts of the world, on all kinds of submarine work, and they are able to boast that never has a defect in their apparatus been responsible for a single death. This is due both to the very careful tests to which every article is subjected before it leaves their works, and also to the thorough training given to their employés.
In the sponge and pearl-fishing industries the diving dress is gradually ousting the unaided powers of the naked diver. One man equipped with a standard dress can do the work of twenty natural divers, and do it more efficiently, as he can pick and choose his material.
This chapter may conclude with a reference to the apparatus now used in exploring or rescue work in mines, where deadly fumes have overcome the miners. It consists of an air-tight mask connected by tubes to a chamber full of oxygen and to a bag containing materials which absorb the carbonic acid of exhaled air. The wearer uses the same air over and over again, and is able to remain independent of the outer atmosphere for more than an hour. The apparatus is also useful for firemen when they have to pass through thick smoke.
FOOTNOTE:
[18.] Vide The Romance of Modern Engineering, p. 212.
[CHAPTER XV]
APPARATUS FOR RAISING SUNKEN SHIPS AND TREASURE
It is somewhat curious that, while the sciences connected with the building of ships have progressed with giant strides, little attention has been paid to the art of raising vessels which have found watery graves in comparatively shallow depths. The total shipping losses of a single year make terrible reading, since they represent the extinction of many brave sailors and the disappearance of huge masses of the world's wealth. A life lost is lost for ever, but cargoes can be recovered if not sunk in water deeper than 180 feet. Yet with all our modern machinery the percentage of vessels raised from even shallow depths is small.
There are practically only two methods of raising a foundered ship: first, to caulk up all leaks and pump her dry; and secondly, to pass cables under her, and lift her bodily by the aid of pontoons, or "camels."
The second method is that more generally used, especially in the estuaries of big rivers where there is a considerable tide. The pontoons, having a united displacement greater than that of the vessel to be raised, are brought over her at low tide. Divers pass under her bottom huge steel cables, which are attached to the "camels." As the tide flows the pontoons sink until they have displaced a weight of water equal to that of the vessel, and then they begin to raise her, and can be towed into shallower water, to repeat the process if necessary next tide. As soon as the deck is above water the vessel may be pumped empty, when all leaks have been stopped.
In water where there is no tide the natural lift must be replaced by artificial power. Under such circumstances the salvage firms use lighters provided with powerful winches, each able to lift up to 800 tons on huge steel cables nearly a foot in diameter. The winches can be moved across a lighter, the cables falling perpendicularly, through transverse wells almost dividing the lighter into separate lengths, so as to get a direct pull. If the wreck has only half the displacement of the lighters, the cables can be passed over rollers on the inner edges of the pontoons, the weight of the raising vessel being counteracted by water let into compartments in the outer side of the pontoons.
There are ten great salvage companies in the British Isles and Europe. The best equipped of these is the Neptune Company, of Stockholm, which has raised 1,500 vessels, worth over £5,000,000 sterling even in their damaged condition, among them the ill-fated submarine "A1." Yet this total represents but a small part of the wealth that has gone to the bottom within a short distance of our coasts.
Turning from the salvage of wrecks to the salvage of precious metal and bulky objects that are known to strew the sea-floor in many places, we must notice the Hydroscope, the invention of Cavaliere Pino, an Italian.
In 1702 there sank in Vigo Bay, on the north-west coast of Spain, twenty-five galleons laden with treasure from America, as the result of an attack by English and Dutch men-of-war. Gold representing £28,000,000 was on those vessels. Down it went to the bottom, and there it is still.
So rich a prize has naturally not failed to attract daring spirits, among whom was Giuseppe Pino. This inventor has produced many devices, the most notable among them the hydroscope, which may best be described as a huge telescope for peering into the depths of the sea. A large circular tank floats on the top of the water. From the centre of its bottom hangs a series of tubes fitting one into the other, so that the whole series can be shortened or lengthened at will. Through the tubes a man can descend to the chamber at their lower extremity, in the sides of which are twelve lenses specially made by Saint Gobain, of Paris, which act as submarine telescopes.
Pino's hydroscope has been at work for some time in Vigo Bay, its operations closely watched by a Spanish war vessel, which will exact 20 per cent. of all treasure recovered. While the hydroscope acts as an eye, the lifting of an object is accomplished by attaching to it large canvas bags furnished with air-tight internal rubber bladders. These have air pumped into them till its pressure overcomes that of the water outside, and the bag then rises like a cork, carrying its load with it. An "elevator"—nine sacks fixed to one frame—will raise twenty-five to thirty tons.
So far Cavaliere Pino has salvaged old Spanish guns, cannon-balls, and pieces of valuable old wood; and presently he may alight on the specie which is the main object of his search.
Another Spanish wreck, the Florida, which was a unit of the Spanish Armada, and sank in Tobermory Bay, the Isle of Mull, has many times been attacked by divers. The last attempt made to recover the treasure which that ill-fated vessel was reputed to bear is that of the steam lighter Sealight, which employed a very powerful sand pump to suck up any objects which it might encounter on the sea-bottom. Many interesting relics have been raised by the pumps and attendant divers—coins, bones, jewels, timbers, cannon, muskets, pistols, swords, and a compass, which is so constructed that pressure on the top causes the legs to spread. One of the cannon, fifty-four inches long, has a separate powder chamber, the shot and wad still in the gun, and traces of powder in the chamber. It is curious that what we usually consider so modern an invention as the breech-loading cannon should be found side by side with stone balls. The heavier objects were, of course, raised by divers. In this quest also the treasure deposit has not yet been tapped.
[CHAPTER XVI]
THE HANDLING OF GRAIN
THE ELEVATOR — THE SUCTION PNEUMATIC GRAIN-LIFTER — THE PNEUMATIC BLAST GRAIN-LIFTER — THE COMBINED SYSTEM