By W. B. A. —-
“O’er the wild gannet’s bath came tho Norse Coursers.”
And to a goodly land they came, bearing the seed of the Norse gods, to take root in the ocean bounded soil of freedom, where tho salt from the veins of the Vikings remains to this day undiluted in the veins of their descendants. Ocean born, they “go down to the sea in ships,” not along a river current, to catch a startled glance and so return, but to sport in its waters, which are their gain, their glory, their delight; the merchant’s highway, the sailor’s battle-field, the sick man’s renovating bath, and the racecourse of the wealthy chiefs and leaders, whose revenues vie in producing the swiftest keels and the safest sea boats.
Once upon a time a rival amongst their western kindred came hither with a craft fashioned like those of pirates in the eastern seas, with stiff flat sails, and a spoon-shaped bottom, and by a trick out-manoeuvred our Fairy Queen and won the prize. But it was a trick — a vessel without space to hold a crew between her ribs, a fair-weather craft without a hold; a craft to which her crew might cling like the parasitus outside a whale, but in which they could not be said to live.
And so after being a nine months’ wonder, and startling some few yacht-owners from their self-possession, causing them to sell their yachts for little or nothing to sharp purveyors of foreign fruit, this far-famed “America” came to “wear a broom” in vain, and now lies somewhere “along shore” in dirt and rags, no one caring to become her possessor. The coasts of the Narrow Sea are not an arena for toy craft, for fair-weather birds. He who would fain skirt them in all weathers needs a craft that may laugh the tempest to scorn, while watch and watch can take alternate ease in dry berths.
The “wooden walls of Old England” were very different things from those wooden walls which the oracle advised the people of Athens to adopt — the oar-impelled galley — the sea-ram of old, with its brazen horns or beak to transfix its opponent galley, involving no small amount of skilful manoeuvring and with very inadequate power. Our “wooden walls” have done good service in their time; but wood is a material adapted only for vessels of a comparatively small size.
Beyond a certain limit the bolts and fastenings crush the grain, and draw out. It becomes necessary to bind the parts together with straps and plates of iron, and in each case it is better to make the entire casing of iron, and to use the wood only as a packing. Wooden ships, ere steam propelled them, required to be carefully guarded against fire. To put steam furnaces into a wooden vessel is a clear tempting of Providence. The internal fires dry the whole of the timber to the condition of tinder. Once on fire, there is no chance of extinguishing it. Upon the same principle that locomotive and steam engines arc prohibited from being used in public when in a dangerous condition, steam engines ought to be prohibited from use in wooden vessels altogether, unless the wood ‘be used simply as a packing, and chemically treated so as to render it unburnable.
For war-ships one of the chief qualities required is speed. Other things being equal, the fastest vessel will be the most powerful, being able to attack her opponents at pleasure and to retreat at pleasure, and, moreover, to strike the weakest part of her opponent. And, other things being equal, the largest vessel will be the fastest if moved by internal power. Using the wind as a moving power, the speed will vary with the class of vessel. The large vessel will move fastest in a heavy gale, the small vessel will have the advantage in light winds.
For mercantile purposes a sailing vessel is best, leaving the whole of the hold for stowage, in regions where the wind blows for months together in a given direction. For certain purposes an auxiliary screw of small power is useful, as, for instance, to help a vessel over the calms of the Line. But for war-vessels, except in districts where fuel is not procurable, sails— unless mere lower sails—are best dispensed with, and steam, or any power which may ultimately dispense with steam, had better be exclusively used. If shot strike the masts and sails of a war vessel, her power of locomotion is impeded, and she will lie at her antagonist’s mercy. In war vessels sails are useful for travelling purposes to save fuel, but internal propulsion is best for fighting.
In point of speed, the largest ships will have the greatest advantage in rough weather, for a very obvious reason. The small vessel partakes of every motion of the waves, and works up and down hill, impeded by every fresh movement. The large vessel makes a straight course: she preserves an even keel at her line of floatation, and the waves oscillate past her without disturbing her. With a proportionate size, the largest waves of the ocean are no more to the larger vessel than the ripple on the water of a pond is to the child’s sailing boat.
Iron ships, like most maritime improvements, originated in the merchant service. In their typical form they are of very ancient date. About the year 1800 iron barges existed on the Paddington canal, much in the form of very long square tanks, and a little boy walking with a cynical sectarian Scottish guardian was severely reproved for likening them to Elisha’s miracle of causing iron to swim.
Some of the earliest sea-going vessels of iron were built on the Clyde, and if not very like a whale, they were certainly very like kettles intended to boil a whale in. In fact, the earliest vessels were made by boiler-makers, and all that they appeared to aim at was to make vessels that would keep out water with the greatest possible amount of displacement in the most convenient form for riveting together without regard to movement. They were mere shells without ribs or framing; and though very safe as regarded mere water-pressure, utterly without strength if they struck an obstacle.
They were cheaper than wooden vessels, and carried more bulk and weight in proportion to their displacement. About a foot in thickness was added to the cubic capacity of the hold over sides and bottom. Of the unseaworthiness of this kind of craft an example was given in the Tayleur, which on her first voyage struck a rock on the Irish coast, and went down instantaneously in deep water with every soul on board. Again, the possibility of making them sufficiently strong was demonstrated in the case of the Great Britain, which lay for four months on the rocks at Dundrum Bay, exposed to the whole thrash of the Atlantic, and was got off a serviceable vessel at last.
Wooden vessels are constructed of a framing of timbers, which in war-ships are put together solid, and covered with a skin of planking inside and out. It was long before economy of cost would permit the idea that an inner framing was essential to give form and strength to an outer iron skin, imitating thus the ancient coracle formed of a leathern skin on a wicker basket, not without form, but with a very bad form, and void. Precisely of such structure is the Esquimaux canoe, built, like our Thames’ wherries, in the best form for skimming the water.
Even when it had been decided that ribs were essential to iron skins, it was still considered necessary to retain the old practice of making the deck beams of wood, and the decks of fir planks caulked, decks which in dry weather required to be treated like the sides and bottom—kept wet to prevent them from leaking. The phrase “washing decks” meant, in truth, wetting decks to keep them from chinking open. The cleanliness grew incidentally from the necessity of the after “swabbing,” and, gradually, fastidious masters’ mates took to spending their own money in lemons to whiten them, till the phrase ” as clean as a ship’s decks” became a sea proverb.
At length a move was made in the Great Eastern. A ribbed framework of iron was covered with an iron outer skin and an iron inner skin, and the whole was divided into water-tight compartments, fore and aft and athwart ships, so that if one or more compartments filled, the others would float her. The practice of watertight compartments obtained early in iron vessels. The Nemesis steamer, sent out to India by the East India Company, after beating the Admiralty in a long paper warfare — Steam versus Wind — was built of iron, in compartments ; and, practically, she decided the first Chinese war in our favour, though, one day, a rock or a Chinese shot —random, of course—struck her exactly at the partition of the two hinder compartments, and she would have sunk, but that the forward partition kept her floating.
Our Scotch friends in the Clyde built some peculiar vessels, very flat-bottomed, with the intention of getting direct from Glasgow to Liverpool over the river shallows; these were divided by water-tight compartments, but they had great alacrity in going to leeward, not being provided with lee boards like our coasters and the Dutch craft. One of them took to the rocks on the Isle of Man, lying in their lee-way, and great exultation was exhibited by the rival owners of wooden craft at the failure of the new-fangled device. But in truth it was only a proof in favour of the scheme; for the canny owners of the iron craft, finding she would stow more cargo with a clear run in the hold, took out the water-tight compartments, and so ensured her sinking.
In addition to her double sides and bottom, the Great Eastern has another improvement. For the first time the decks also are of iron, and therefore for the first time an incombustible ship is attained. Shylock’s phrase, “ships are but boards,” no longer holds good. It is true that the compartments may be filled with combustibles and set on fire, or they may be blown up with gunpowder, but any one compartment may be drowned without risk, to put out a fire; and it is not an impossible thing so to stow the gunpowder that the minimum of damage may be inflicted by explosion, and the vessel remain a seaworthy craft notwithstanding.
The Admiralty built a number of iron steamers, imitating, as is always done, the experience of the merchant service. It then occurred to try their shot-proof capacity. Cast-iron shot splintered in going through their sides, and some of the projectiles drove in two square yards of plating at a blow, precisely as the Irish rock stove in the sides of the Tayleur. The plates broke away entire along the lines of rivets.
This leads us to the question of riveting—a very imperfect process. In round numbers, the strength of a vessel at the rivets is only two-thirds that of the solid portion, even when the riveting is carefully and honestly performed. But a large portion of the riveting is simply hand-labour, and the labour of many hands. The operation of punching holes does not always bring them opposite to each other, and a second operation, called “drifting,” takes place, skewing the rivet from one hole to another. In some cases the bad workman who has caused the defect covers up his bad workmanship with a leaden rivet. The most careful supervision cannot always guard against this.
Let us begin at the beginning, and find out what we want step by step. First, the ship should be such as cannot be sunk by collision. The bottom should be of the strongest possible structure. The fire-box of a locomotive engine furnishes an example of this. Two skins, some four inches apart, are connected by stay-bolts four inches from each other, and the pressure of steam, twenty tons to the square foot, between them, has no power to rend them asunder. If the pressure, instead of being internal were external, and the hollow space were filled up with solid matter between, the strength of resistance would be increased many fold.
Again, if a surface of iron plates, riveted together and extended on an open frame, be struck with a shot, a large mass will be driven in. But if the whole volume of the plates be lined with a solid mass of timber, of sufficient thickness, the shot will simply punch a hole in the iron plates.
If, therefore, we construct the bottom of the vessel, and part of the rising sides, of two skins, say four feet apart, with parallel surfaces, stayed with strong stays four feet apart, and then fill the enclosed space with hot bitumen mingled with blocks of wood or with stone ballast, the bitumen when cold would be a tough substance, and the whole would form a solid body that, if it struck a rock, might have a hole punched through its outer skin, but scarcely through the inner skin, which would dingo upwards. If the rock broke through both, then the compartment system would limit the damage to a small portion of the vessel. With hot bitumen run in between the two skins, no mischief could take place by rust. The whole floor might, for greater security, be composed of three skins, making up a thickness of six feet.
But this supposes the ordinary process of riveting the plates together. If the plates could all be welded together in one piece instead of riveted, the same strength would be obtained with two-thirds the thickness of metal, or with the same thickness of metal one-third more strength would be attained. Could this be done, a vessel might be constructed with the entire shell, deck and all, in a single piece of malleable iron, as entire as the skin of a whale.
But this has not yet been done. No; and there was once a time when no iron vessel at all had been built. One thing is certain—iron has been welded together in larger or smaller pieces, more or less perfectly, from a very distant date.
What, then, is welding?
Heating the surfaces of two or more pieces of iron to a pasty or just melting condition, and bringing them into close contact, free from all scale or dirt, in which case the two or more pieces become one.
Scale is produced by atmospheric air impinging upon hot iron, and no union can take place while scale exists between the surfaces. But without atmospheric contact scale does not form. If a polished watch-spring be bedded in powdered charcoal, covered over in a crucible, and kept red hot for a week without atmospheric contact, and then be suffered to cool gradually, it will come out without loss of polish. Every one knows that in the burning of an ordinary tallow-candle carbon is formed in the shape of what is called the snuff, and that this snuff goes on increasing in bulk till it rises above the bladder of flame which encloses it. H the candle be considerably inclined out of the vertical position, the carbon is protruded beyond the wick, atmospheric contact is induced, and the carbon is burnt away.
If flame can be made to impinge on iron surfaces, so as to shut out the atmosphere, scale will not be formed; the flame consumes the oxygen of the atmosphere, and prevents it from approaching the iron.
In ordinary welding the iron is put into a furnace, or into a smith’s forge. It is rare that more or less scaling does not take place. The smith tries to prevent it by throwing sand on to the iron, which melts into glass, and so shuts out the atmosphere. In these cases the coal with sulphur and other impurities is brought into contact with the metal. What is wanted is, not the coal, but the hydrogen and carbon producing flame and heat by impact. It is therefore worth inquiring whether this cannot be done in a better mode and with better management. There does not seem to be much difficulty.
The oxyhydrogen blowpipe gives us the most intense heat we know of. If therefore a reservoir of hydrogen gas under pressure be made to communicate with a pipe and nozzle, and atmospheric air under pressure be used in a similar mode, and fire be applied, where the two unite, the result is a welding heat. If instead of a single nozzle, a combination of nozzles, or pipes with a continuous row of holes, be used, a flame of any length may be produced. This flame might be made to impinge on the joints of iron planks the whole length of a ship’s side, in such a manner as not to burn away the sharp edges of the plates, but to cover the surface so as to prevent scale, and produce a welding heat through the whole length, and thus simple pressure would effect a welded joint. The metal would become homogeneous. If this can be done (and there seems no reason against it), we shall attain strength and durability hitherto unaccomplished.
The next question is that of propulsion — the power to propel, and also the instrument to propel with. Steam is at present our best power, but it has its disadvantages. The power is not generated at the moment of action. It needs a reservoir, and the reservoir may burst. Magnetism differs from this, if we could only use magnetism. Then steam needs fresh and pure water, not easily to be had on the ocean. Again: steam needs fuel, which is very bulky and takes up space, and is moreover explosive, under certain circumstances, as well as the steam it helps to create; but withal steam is the best power we know of at present, and we must work with it till we get a better.
We call the engine a steam-engine, but it is in reality a heat-engine; the water gives out power in proportion to the heat it absorbs, and all power appears to resolve itself ultimately into heat. Whether it be the power of steam, or magnetism, or electricity, or wind or water, or the power of animal muscles —whether elastic power or the power of gravity — all seems to resolve itself into the question of heat.
Many disputes have arisen as to whether circular movement or rectilinear movement is best for the prime mover; but thus far opinion seems to be in favour of the latter; and the next question is as to the instrument. The paddle, the screw, and the pump are up to this time the efficient means. Steam-moved oars have been tried, but with inefficient results. The paddle is out of the question for war-ships, even supposing it more efficient for speed than the screw. The best made paddles should enter the water at one corner, but so as to make no blow, and in that case they would approximate to the action of the screw; but the side of the vessel would be a very awkward position for the screw. It is proved that the best screws are those that enter the water gradually, with rounded corners.
The first propulsion by pump was tried by Dr. Franklin, who got astride of a wooden ship’s pump in a pond, and found that by working the handle he could move himself along. The last trial was by a centrifugal pump, similar to that shown at the Great Exhibition, pulling the water in at the fore end of the vessel and discharging it on each side abaft. A single pump was used, and it was found that by delivering the water at a nozzle on each side, with a moveable month, the vessel could be made to move forward or backward, or to turn round, at pleasure. It is yet a disputed point how much more power is lost by the pump than by the screw; but when we remember how many years we have been by slow processes getting the screw to its present condition of utility, there is little doubt that further experiments will give important results with the pump. The same screw that we apply at the stern of a vessel wherewith to propel, serves equally well to raise water when applied as a pump, if the sides be inclosed to form a bucket.
One thing is certain, the stern screw is much more out of the way than the side paddles or screws, and the pump in the bottom is still more out of the way than the stern screw. There is nothing to get foul in the ease of the pump, and in a war-ship even something of speed might be sacrificed for such an important object.
While we use explosive boilers, it is worth while to consider how to minimise the danger if an explosion does take place. The usual course of explosion is upwards, like gunpowder; and therefore if the boiler be confined within firm wrought-iron walls, there need be no communication to the boiler space save by the furnace and ash-pan doors; and in such case the stokers might be kept comparatively cool by constant currents of air passing over and around them, in contradistinction to the present very common practice of nearly roasting them alive.
Apart from the cruelty to the men, this is no trifling matter in point of safety to crew and passengers. No man can do his work well and thoroughly while his bodily sensations are those of pain and discomfort, and even inspection cannot be well performed with unwilling workmen. We have no right, as we are not despots, to roast people alive in a stoke-hole, and shall infallibly get punished for it, by their doing what they ought not to do, and leaving undone that which they ought to do.
Examination of valves and all other matters can be provided for, without having the heated boiler in close contact with the stokers. A war-ship depending wholly on the management of her steam, would be in great peril if the condition of her boilers were such as to drive the men away at intervals to get fresh air, as we so commonly see in our river passenger-steamers.
Supposing the walls of the boiler space to be carried up a sufficient height above the deck like a square chimney, and roofed over only sufficiently strong to keep out wind and water, the probable result of an explosion would be similar to that of a gun placed vertically. It would blow the steam and all fractured portions upwards, with little mischief and without permeating horizontally, and scalding the men; and the boiler could be arranged so as to make the upper portion the weakest part, thus determining the fracture to the line of safety, if burst by over pressure. It is obvious that in the construction of boilers the same principle ought to obtain as in the construction of the vessels, viz., to get rid of rivets, and to substitute solid welding, even if the question involved a change of form in the boilers, so arranging them as to make all parts capable of being welded.
In all vessels there is one line of floatation or displacement which involves the least amount of retardation through the water. In the ordinary arrangement of vessels this varies in proportion to the consumption of provisions and water by those on board. In steam-vessels, the item of coal-consumption makes a much more serious difference. In the Great Eastern this difficulty is met by pumping sea or other water into the various compartments to replace the weight consumed.
From the time that iron tanks were used instead of water-casks this plan has been resorted to, but in steam-vessels, with fixed pumps and pipes, and with steam to do the work, the old plan of ballasting by shingle or gravel may be dispensed with. Water ballast is the most convenient arrangement, and, placed in close cells so that it cannot shift, it is the safest of any kind, for common ballast may shift by the rolling of a vessel. Moreover, no other ballast than water can be procured at sea to supply the daily waste.
(To be continued.)