“This question of stability will have to be carefully watched and studied within the next few years, because there is a tendency at present towards a rapid increase in the proportion of beam to length; and as the draught of water in these large ships is limited, we must be careful that in seeking higher speeds with increased beam we do not get too much stability, and so render the vessels heavy rollers and very uncomfortable as passenger-ships. It is possible the future may see vessels of greater beam than any yet afloat in the merchant service; but if so, it is almost inevitable that they will have to be made higher out of water in order to render them easy and comfortable at sea, but even that has its limits. Perhaps it is well to give an extreme case, and here I will make use of our old friend The Great Eastern.... Now, for the purpose of trading it is quite clear that The Great Eastern cannot be loaded much deeper than other ships, while her beam is half as great again; and the consequence is, her stability, as compared with our modern passenger-ships, is so excessive that she is bound to be a tremendous roller among the heavy seas in the Atlantic. Her metacentric height, when loaded, was, I believe, stated by the late Mr. Froude to be as much as 8.7 feet, which is from three to four times as much as is thought sufficient for ships in the present day, or consistent with their easy behavior at sea.”
Thus Mr. John himself regards 2.9 feet to 2.2 feet as the proper metacentric height for those steamers, and it is generally considered by modern designers that from 2.5 to 3.2 feet is most suitable for this class of armored ships, and is conducive to easiness of motion in a sea-way. The value of this quality to a ship intended for sea-fighting cannot be overestimated, for upon her steadiness as a gun-platform the aim and efficiency of her guns greatly depend.
It will be noticed that this ship has exceptionally great beam, that of most ships of her class and displacement, varying from 54 to 59 feet, and judging from the sketches which have appeared, her water-line coefficient is about 0.72. From an approximate calculation based on this assumption it is found that her metacentric height will be about six feet. The water-line coefficient may possibly be a little finer than 0.72, and thus reduce the metacentric height, but if this ship is assumed to have a metacentric height of three feet, her water-line coefficient would be 0.6288, which is an impossibility, if her coefficient of fineness of displacement be that given in the published dimensions. Such a water-line and coefficient of fineness for 6300 tons displacement would produce a perfect rectangle for a midship section. So that, unless her dimensions are changed, she will surely be a heavy roller, and after much sea duty she will suffer such severe strains as to require frequent and costly repairs.
The battle-ship designed at the Navy Department has very different qualities, if the dimensions already published be correct. To possess a metacentric height of three feet she would require a water-line coefficient of 0.753, and a midship-section coefficient of 0.89 to 0.90, which is a good proportion for such a vessel. Not only in sea-going qualities does the American design seem to be superior, but her battery is far more powerful and better disposed in every way, while her speed and endurance are equally as great as the plan recommended. Mr. John has adopted the échelon arrangement of heavy guns, a disposition which both the English and Italian governments have, after long trial, discarded in their latest ships. When the first sketches of a design are made, this arrangement of guns is theoretically perfect, as it is supposed to give quite as much power of fire ahead and astern as on each broadside; but when the design is developed and practically tested, it is found that too much of the ship’s efficiency in other respects is sacrificed, that the powerful end fire is not attained, and that the broadside is greatly weakened, owing to the obstructed arcs of fire.
Besides this, the guns, being placed at some distance from the midship line, have less accurate fire in rolling, and the ship’s propensities to roll are encouraged and are greater than would be the case if the guns were placed on the midship line. It is also found that the blast from the heavy guns is destructive to superstructures and other fittings on the upper deck. The Italians, indeed, have placed stout ventilating shafts on their Italia and Lepanto to prevent the rearmost pair of heavy guns from being trained within twenty degrees of the fore and aft line. This is done so that the blast from these guns will not prostrate the gunners attending the other pair, notwithstanding the fact that those men are under the armor cover. The Duilio’s forward smoke-pipe is placed entirely on the port side of the fore and aft line, in order to permit of one pair of turret guns firing ahead. The upper-deck, 6-inch, central-pivot guns of the Andrea Doria class are now to be placed wholly within the superstructure, in order to be out of danger from the blast of the heavy guns when the latter are fired near the line of keel, and the same change would have to be made with the upper-deck, 6-inch guns in the Barrow design.
Similar objections exist to the Bureau of Construction design for an armored cruiser. This vessel, although possessing the bad features inherent in the échelon arrangement of heavy guns, does not have the best ideas of the Barrow design, i.e., high freeboard, heavy guns mounted high above the water-line, and commodious quarters for officers and men. Both designs besides have the very objectionable and old-fashioned features of requiring the turrets to be revolved to fixed loading positions after being fired. The Bureau cruiser, it may be said, is not saddled with too much metacentric height. She has ten feet less beam, her centre of gravity is about one foot lower, and unless her water-line coefficient is very full, she will have a metacentric height rather less than what is regarded to be the best.
It is not surprising, however, that the Bureau plans are so different in efficiency, for while the better plan, the battle-ship, is original with the Navy Department, the armored cruiser is a copy of, and no substantial improvement over, that of the Brazilian ship Riachuelo designed several years ago. This ship is considered one of the best of her date, but great improvements in ship design have been made within the past few years, and it is against the tendencies of American inventive genius to take a step backward.
The general plans of cruisers No. 4 and 5 were published in the New York Herald of June 1st, together with the following data:
“They are to be twin-screw cruisers, 310 feet long on the water-line, 49 feet 1¾ inches extreme breadth, 18 feet 9 inches mean draught, displacing 4083 tons. They are to have machinery of 10,500 indicated horse-power under forced draft. The maximum speed is 19 knots, rig that of a three-masted schooner, spreading 5400 square feet of sail. They will have a double bottom extending through 129 feet of the length. The framing in this portion is on the bracket system. Before and abaft the double bottom, above the protective deck, Z-bars form the transverse frames. The protective deck, which is nineteen inches above the water-line amidships, is flat across the top, with sides which slope down to a depth of four feet three inches below the water-line. The horizontal portion is two inches thick, the slope being three inches, reduced at both ends to one and a half inches. It extends uninterruptedly forward and aft, and protects the machinery, magazines, and steering-gear, the machinery being further defended by the disposition of the coal-bunkers. The main hatches in this deck are protected by armor-bars, and have coffer-dams extending to the upper deck. The guns are carried on the gun, forecastle, and poop decks.