Nowadays sailing ships are few in number and are becoming fewer, and steamers seldom require aid. They enter and leave port under their own steam and even at times dispense with a tug when passing through the dock entrance, their own steam or a steam capstan ashore being found sufficient.
But a certain amount of towing has still to be done, and the tug is then able to prove herself indispensable. She has often to tow a ship from one coast port to another, while for rescue work on the coast their services mean all the difference between success and failure. A lifeboat is towed to a wreck or vessel in danger. The tug, which has perhaps been several hours fighting her way forward against a howling gale and a terrific sea which threatens to overwhelm her, then stands by, and a paragraph in the papers to that effect is about all the recognition she gets, yet the perils undergone by the men on the tug are no less real than those of the lifeboatmen. Year in and year out the tugs pursue their calling, and it must indeed be bad weather that will induce a tugboat captain to seek the shelter of a harbour if his bunkers are fairly full and he sees a chance of doing business.
The feats performed by some tugs are extraordinary. They will undertake a voyage of a few thousand miles as serenely as one of as many yards. Cleopatra’s needle, in its strange cylinder ship, was towed to this country, after being lost adrift in the Bay of Biscay, by a well-known London tug. Among the most remarkable recent feats are the towing of immense unwieldy floating docks from this country to South American west-coast ports; it is not too much to say that a tug-owner will cheerfully undertake to tow anything that will float from any one seaport to any other.
The cargo steamer until ten or fifteen years ago possessed no special features. It was simply a big box carrying propelling machinery and as much cargo as possible on the smallest attainable registered tonnage. Such vessels were usually loaded and discharged by the necessary machinery on the quay side, while if the transfer of cargo had to be to or from barges alongside, the operation was likely to be tediously performed by means of a derrick or two, or a gaff with tackle that might or might not be worked by a steam-winch. The increasing size of vessels and the use of steel for steamer building rendered imperative the adoption of faster methods, and the demands for special steamers adapted for particular trades brought about the development in cargo steamers of special types. These types have to a very large extent taken the trade away from the steamer of the “tramp” class, which wandered from port to port taking cargoes of anything or everything from anywhere to anywhere. They were usually slow and uncomfortable boats and the complaints made as to the condition of some of them were fully justified. The demand for better cargo accommodation was met by the supply of vessels of various types which are a tremendous advance upon the old “tramp,” and their advent compelled the builders of ordinary cargo carriers to produce a better and larger steamer in every way, and fitted with modern appliances for the rapid and satisfactory handling of cargo.
The cargo “tramps,” built about 1902, were on an average about 350 feet long, 2800 tons gross and 4000 tons dead weight. In build they were of the poop, bridge, and forecastle deck type with main deck below the upper deck, and fitted with double bottoms. The appliances for working cargo are extraordinarily complete and effective. To each hatch there are usually two winches and two derricks, having 5 tons lift each, with, as a rule, a heavy derrick capable of lifting from 20 to 30 tons; the last is portable, so that it can be used at either of the two main hatches. Cathead davits have been dispensed with as, with stockless anchors, they are not required owing to the anchors stowing up the hawse pipes. Officers, &c., are berthed in deckhouses built on the bridge deck, leaving the bridge ’tween deck clear for cargo. Electric light and steam-heating are fitted to all rooms, advantages not enjoyed by older boats.
About the year 1904 the shelter-deck type reached its present stage of perfection, the advantage of this type being increased cargo capacity on a small net tonnage. The accommodation of officers and engineers is fitted in midship deckhouses and side houses. Much more attention is now paid to the ventilation of the holds and ’tween decks, more especially in coal-carriers, where efficient ventilation is of the highest importance. The adoption, within very recent years, of wide-spaced pillars in holds and ’tween decks has greatly improved the facilities for stowage of large cargo.
The four desiderata of a modern cargo-boat are that she should have a low registered tonnage in comparison with her capacity, ample water-ballast tanks, large hatchways, and holds as free from obstruction as possible. Three or four methods are practised by builders for attaining these objects, and every builder has made modifications of them as time has shown the necessity of the changes to meet varying trade conditions.
The principal types of cargo vessels are the turret, trunk, cantilever, and side tank.
The earlier modern ocean-going steamers were usually flush-decked. This left the machinery openings bare in the deck, so a bridge was added for their protection, and the flush deck was further encroached upon by the addition of a forecastle and poop. In some cases the quarter deck was raised, which was an awkward arrangement on account of the change it necessitated in the structure and framing, and in others the bridge and poop were joined. What is sometimes called the “three island” type, a very appropriate name in rough weather when the steamer takes a sea on board, came into great favour; it consists of a forecastle, bridge, and poop, and many vessels of considerable size have been built in that style. The cattle trade was responsible for some important changes in design, the “wells” where the cattle are carried being given iron and steel shelters, which thus form the shelter decks, a type of light deck introduced into the superstructure of most ocean-going steamers.
The secret of the turret steamer is strength without unnecessary weight. Every ton of steel that can be kept out of a ship without reducing her strength adds a ton to her carrying capacity. This object is partly achieved in the turret steamer by the large amount of flanging adopted in the construction of these vessels. This is shown in the whole of the sheer strake and stringer plates, in the deck and frames of the cellular bottom work, and with great success in the joggled plating of the hull. Since 1895, when the Doxfords introduced a new method of rolling ships’ plates with joggled edges, they have built all their vessels under this system, making “packing” unnecessary. The turret gives longitudinal strength in the hull and leaves the hold clear. The strength is so great that in a steamer in which, by the substitution of deep for ordinary frames, all internal supports, beams, and girders are dispensed with, a clear hold is obtained. The firm claims that 58 cubic feet per ton dead weight under hatches is secured against 52 to 54 cubic feet per ton in the ordinary type. Thus the turret carries more on a given displacement, and having a lower registered tonnage, can earn more freight and save expenses. There are several designs of turret steamers adapted to different trades. Their suitability for bulk cargo, such as coal, or for large and heavy packages, is evident, while other types are equally suitable as passenger steamers, not a few lines having adopted them. Another advantage is that deck cargoes of wood can be carried with perfect safety on the turrets. Some of the cargo-boats designed for the ore and coal trade have their machinery right aft, and their holds are absolutely clear of obstruction of any kind whatever. Many of these are mastless but are fitted with twin derricks, a 10,000-ton boat carrying as many as seven pairs. The first of the mastless type was the Teucer. Convention fixed the depth of hold at about 15 feet, but now a depth of 26 feet and more is becoming fairly common. All cargo vessels are built on the box-girder system, which ensures great strength and capacity, and permits of enormous hatchways, and marine engineers have solved the problem of providing greater speed without additional expense.