Steamships and their story

by E. Keble Chatterton

There are two types of rudders fitted to steamships. These consist of the ordinary kind when the rudder is hung at its forward edge, and the balanced type which has part of its area forward of its axis. An example of the former will be found in the case of the White Star Laurentic, while the Mauretania and Lusitania each has a balanced rudder. Since it is necessary to the rudder that to obtain steerage effect there must be the motion of the ship through the water, or a flow of water past the rudder, so that an excess of pressure may be obtained on one side of the latter, it is possible for the steamship to possess steerage way actually before she has obtained motion; for the propeller race brings this about in an effective manner. The advent of the twin-screw system was responsible for a material increase in the turning possibilities of the ship, an advantage which was much appreciated when already the steamship had attained such enormous dimensions in regard to length. Thus, for example, supposing a twin-screw steamship wishes to turn quickly to port, she can do this by starboarding her helm, putting her port engines astern, and her starboard engines ahead. The advantage of the balanced type of rudder just mentioned is that it is easier to put over than the ordinary type, but it demands that the deadwood of the stern should be considerably cut away.

It is only comparatively recently that the full importance which it deserves has been granted to the naval architectural experimental tank, but these interesting objects are now becoming more numerous, and yielding most valuable data on which to work. Fifty years ago naval architecture in Great Britain was certainly not on a scientific basis, and it was to France that we had to look for the leadership in these matters. But ever since the founding of the Institution of Naval Architects, and such men as Scott Russell, Sir Edward Reed and others led the way, scientific shipbuilding began to advance in this country. The results are evident in the shipbuilding history of our Royal Navy, as well as in the excellence of our splendid merchant fleets. In elucidating the many problems connected with ship architecture the experimental tank is now taking even a more prominent place than hitherto, and the recent opening of the National Experimental Tank at Bushey, where research will be carried on continuously without interference from commercial considerations, is deserving of the warmest congratulations. One of the most important tanks in the world is that owned by Messrs. John Brown and Co., Ltd., at their Clydebank works. Indeed, it may be said that no feature of this important yard is more deserving of interest. The tank is 400 feet long and 20 feet wide, with a depth of 8 to 9 feet. At the end of the tank, where the models are worked, are dry and wet docks for trimming these little ships, which are sometimes as large as 20 feet long. The latter are made of wax, carefully moulded, and their weight is automatically registered. There is an over-head rail for removing the models from one place to another, while the carriage from which the model is towed through the water runs on rails fixed on each side of the concrete walls of the tank, and is driven by electricity. At about the centre of the main tank building there is an observation room which is used for photographic purposes. Messrs. John Brown and Co. themselves have admitted that it is owing to the valuable experiments obtained in this tank that they have been able to design ships producing the best results, whilst also exhibiting the maximum economy.

Mathematical theories and formulæ have contributed much to the development of the steamship, but there is a point reached when these are of no avail for the reason that when new problems arise that cannot be solved by former experiences and existing data, a more practical method of obtaining information must be found. It is here that the tank comes in to solve the difficulties at hand both as to the hulls of the ships themselves and the character of the propellers which are to send them through the water. Had the experimental tank been encouraged at an earlier date, no doubt certain of the errors which characterised some of the ships of the sea might have been avoided. It is not enough to build a steamship of enduring strength, and to give her the best engines of the time; it is also essential that she be designed in such a manner that her propellers forge her ahead with the minimum of resistance.

Germany and America, no less than Great Britain, are now busying themselves with the employment of the naval experimental tank, and obtain thereby so many valuable data as to make such institutions indispensable if advance in the science of naval architecture is to be something more than ephemeral. The Norddeutscher Lloyd Company had such a tank built in 1900 on the model of the one belonging to the Royal Italian Navy at Spezia, and some description may not be without interest. The tank is contained in a building 170 metres long and 8 metres wide. On either side of the tank is a strong set of rails on which the towing carriage runs, and the building contains workshops wherein the models are constructed. The experiments are not complicated, for after the displacement of the projected ship has been decided on, several models of such a displacement are made from drawings by means of an ingenious machine. These models are made out of paraffin wax, and about 4 or 5 metres long. (A metre, it should be remembered, is the equivalent of 1·094 English yards.)

Presently, after they have been finished off, the models are towed through the tank, and their resistance is measured by a dynamometer, the automatic drum simultaneously measuring the course and time. It should be mentioned that it is after the models have been formed in sifted clay that they are cast in wax as a hollow shell, the core being made of battens, strong canvas being also employed. After the model has been subjected to the cutting machine, it is planed and scraped by hand to remove the excrescences of paraffin. The advantage which the experiments made in tanks give lies in the fact that one can thereby ascertain the resistance which the model will encounter through the water, and consequently the amount of effective horse-power that she will require. Granted that an owner desires to have built a steamship of a certain displacement, it follows that that amount of displacement is capable of being embodied in numerous different shapes; and it is part of the work of the experimental tank to determine the most suitable ratios of length, breadth and draught which shall produce the ideal ship for the purpose desired. Indeed, it may be said that it is only by means of the experiments made in tanks that any safe and reliable method can be afforded for attaining the desired end.

The model is made according to scale with a displacement proportionate to that of the steamship to be built, and the correct amount of immersion is given to the model by adding ballast in the shape of small linen bags containing shot. In order to obtain the measurements of the model’s resistance in the water, it is placed under the carriage which bears the measuring instruments for indicating both the resistance of the model, and the thrusting and twisting stresses of the model screws. It should be explained that the carriage is moved by motors which derive their current from accumulators, and it is possible, by regulating the accumulators, to obtain over 400 different speeds. The advantage of this in studying the wave formation which the models set up is of the highest importance. To be able to ascertain how much resistance the model sets up at lesser and higher speeds is a great gain, and in no respect is this information more valuable than when experiments are being made with a view to high-speed torpedo boats; but as this kind of craft does not come within our present scope, we must pass on.

We may turn now from some of the more technical problems incurred by the steamship to a consideration of some of those which are of a more practical nature. It is just because the ship has in modern times taken on a dual character—become something else besides a sea-craft—that the possibilities of any accident occurring to her have increased tremendously. It is obvious that so long as you retain simplicity, there is not much chance offered for accident; but as soon as you begin to make the ship a mass of complications, then instantly there arise on every side facilities for mishap of some sort or another. Fractured shafts are happily of rare occurrence, but when they happen at all they are naturally far worse for the single-screw ship than the vessel having two or more propellers. When a connecting rod or piston-rod breaks the matter is serious, for it is not advisable to attempt repairing the same at sea, since unless the thing is done quite effectively, there is danger of the rod giving way again, and if the piston were to be disconnected suddenly from the crank, it would smash the engine. The first time that a tail-shaft was ever repaired at sea was in October of 1900, when the chief engineer of the s.s. Athena successfully brought about so interesting an achievement, and a similar feat was performed about five years later on the s.s. Milton, so that the ship was able to steam at the rate of a hundred miles per day.

But a far more difficult and rarer task was that of the chief engineer of the s.s. Matoppo, who for the first time on record actually renewed the blades of the propeller at sea. This would be no mean performance in the case of fair weather, but, as it happened, there was a high sea running at the time, and the work was rendered both difficult and dangerous. One of the most tiresome accidents occurs when the steamship loses her rudder, or it becomes so much damaged as to be unserviceable. In the case of a twin-screw ship, as we have already intimated, the consequences are not necessarily serious, and ships have succeeded in making long passages steering by means of their two propellers. But in the case of a single-screw ship the carrying away of the rudder is of greater consequence, and it becomes necessary to rig up a jury rudder as well as possible. This consists in towing astern a spar which is attached to either quarter of the ship by means of hawsers.

An interesting experience is related by Commander W. H. Owen, R.N.R., who at the time of the following incident was in command of a screw steamer of about 1,200 tons. When about 600 miles south-west of the Lizard, his ship had the misfortune to carry away her rudder. A jury rudder was rigged up in the usual way by fashioning a big steering oar out of the heaviest derrick which the ship possessed, bolting together iron plates at the outside end, and weighted below so as to keep the blade vertical. From the end steel hawsers were led in through outriggers to the steam winch. This all took time, and it was a day and a quarter before the arrangement was fixed up. When it was finally put into place, it only lasted a few minutes, for the first scend of the ship smashed the whole thing. Other means had, therefore, to be employed, and the ship was eventually steered into Falmouth, where temporary repairs were effected, the vessel then proceeding to Southampton, where a new rudder was made. Commander Owen adds that he considers the best possible arrangement, if such an accident should occur, to be as follows:—A heavy spar should be lashed to as much chain cable as the spar can sustain while yet keeping afloat, the bights of cable being allowed to hang down in lengths of about two fathoms, thus forming practically a solid sheet of iron, the bights of the cable being lashed close together by smaller chain. The contrivance is then towed astern of the ship from the quarters, sufficient scope being given to allow the spar to clear the counter as the vessel pitches or scends, the controlling being effected by means of steel hawsers attached to the other end of the spar, and led through outriggers to a steam winch.

Another kind of disaster which may overcome the steamship is that of fire. Owing to the frequency of this species of calamity, the committee of Lloyd’s some seven years ago instituted a special inquiry into the matter, and after examining no fewer than 627 cases of fire on ships, it was found that as many as 403 had occurred while the ship was in port; thus only about one-third of the instances happened while the ship was at sea. In most cases there was no evidence to show the cause of these fires, but since it was ascertained that many of the outbreaks occurred while the ship was discharging or loading cargo, it was thought that a closer supervision over the use of lights and a more stringent prevention of smoking in the holds would give more satisfactory results.