NATURE 



THURSDAY, JULY 12, 1877 



THE " INFLEXIBLE " 



THE question which has been raised respecting the 

 stability of the Inflerihlc, important as it is with 

 reference to that ship, leads to very much wider and 

 more general considerations. It is already known that 

 the same principle, or want of principle, which has 

 brought doubt upon the one ship appears also in the 

 Ajax and the Agamemnon, and is to be repyroiuced in 

 the only ship of much size or importance which the 

 Government purpose commencing during the present 

 year. But even in this succession of large and costly 

 ships we see prabably but the beginning of a system 

 which, having thus received countenance and sanction in 

 the highest quarters in this country, may not improbably 

 become extended over the navies of the world. We 

 propose, therefore, to explain to our readers the nature 

 of the question itself and the manner in which it has 

 arisen. 



And as an essential preliminary we will first explain what 

 is meant by the terms " stability" and " cur\e of stability." 

 For the purpose of this elementary explanation it will be 

 sufficient to take the case of a ship floating in still water. 

 In Fig. I, which represents the transverse section of a 

 ship taken through the centre of gravity, M represents 

 the metacentre, G the centre of gravity, and E the centre 

 of buoyancy, W L being the water-line when the ship is in 

 an upright position. Supposing the ship to be inclined 

 through an angle of 6 degrees from that position by an 

 external force, and Wji,; to become the new water-line ; 

 she will now tend to return to the upright position with a 

 righting force equal to her total weight or displacement, 

 acting with the leverage of g z, and therefore equal to 

 w X G z. This is obviously the case, because while the 

 ship is held in the inclined position her weight will be 

 acting downwards through G in the direction of G H, 

 which is perpendicular to the water's surface, w, Lj, and 

 her buoyancy, which may be supposed to act collectively 

 through its centre of buoyancy, Bj, will be pushing up- 

 wards through the line B, M, and therefore the righting 

 effect will be that of the two forces (weight and buoyancy, 

 which are alike) acting at the opposite ends of the lever, 

 G z, as previously stated. It is equally certain that in all 

 ordinary forms of ship G z will be changed in length as 

 the ship's angle of inclination is changed, and if we 

 calculate its lengths for a series of angles, and set up 

 the lengths so obtained as ordinates along a base line on 

 which abscissae are measured off to represent the angles 

 of inclination, we can draw a curve line through the 

 points so obtained, and thus form what is called a " curve 

 of stability." The first instance on record of this being 

 done for an actual ship or design is that given in a paper 

 " On the Stability of Monitors under Canvas," read in 

 1868 at the Institution of Naval Architects, and published 

 in their Transactions, and in several other places. After 

 stating the amount of stability which certain rigged 

 monitors would have under given conditions, and showing 

 that the maximum stability, and even the vanishing sta- 

 bility was reached in them at moderate angles of inclina- 

 VoL. XVI.— No. 402 



tion, Mr. Reed said : " It must be obvious that the danger 

 to be apprehended by these monitors when under canvas 

 is very great ; and when we think that they are liable at 

 any moment to be overtaken by sudden gusts of wind, 

 and that if they are heeled over beyond 8 deg. or 10 deg., 

 the further they go the less resistance they offer to being 

 capsised, their unfitness to carry sail must be quite 

 evident." 



The curve of stability was next constructed in the case 

 of the Captain, immediately before her loss, and from a 

 report by Mr. Barnes, one of the present Admiralty 

 constructors, we take the following : — " VVe assume that 

 the side plating on the poop and forecastle has been 

 so damaged that the ship may be considered a rigged 

 monitor with a free-board of about 6 fc. At that draught 

 (25 ft. and i- an inch) with an inclination of 14 deg., the 

 gunwale on the immersed side is level with the water, but 

 the stability of the ship notwithstanding goes on increas- 

 ing until an inclination of 21 deg. is reached. As Mr. 

 Reed has pointed out in his paper (quoted above) on 

 rigged monitors, with a pressure of canvas which would 

 incline the ship to say 8 deg , the inclination of the ship 

 to the surface of the wave may reach about 34 deg. (in 

 this case) before the ship would upset. As this angle is 

 large we do not consider that even with the sides of 

 the poop and forecastle destroyed, the Captain would be 

 unsafe." 



The above cases are both those of rigged ships, which 

 the Inflexible can scarcely be considered, although it 

 must be acknowledged that, as designed, she carried a 

 considerable spread of canvas on two masts, and the pre- 

 sent proposals — which we understand have been made — 

 to diminish the spread of sail at all times, and to do away 

 with it altogether in war time, are no doubt consequences 

 of recent discoveries respecting the stability, or want of 

 stability, of the ship with the unarmoured ends badly 

 injured. After what has passed, however, we must accept 

 the Inflexible as a mastless ship in time of war, and there- 

 fore a ship which can do with less stability than rigged 

 ships require. In order to illustrate the nature and 

 character of these curves we copy, in Fig. 2, a figure 

 from Mr. Thearle's valuable work on " Theoretical Naval 

 Architecture," ' in which he has grouped half-a-dozen 

 curves which may be regarded as types of various kinds 

 of curves of statical stability which occur in practice, 

 viz. : — 



A. A lofty-sided troop-ship, carrying sail. 



B. Do. Do. 



C. A broadside iron-clad frigate. Do. 



D. A turret-ship with high freeboard. Do. 



E. A low freeboard iron-clad gun-vessel, not 



carrying sa'l. 

 P. A breastwork monitor, Do. 

 To facilitate comparison, we have added to Fig. 2 dotted 

 lines showing the rtability of the Captain as ascertained 

 at the Admiralty just before her loss. The curve marked 

 a shows the stability when the ship is fully stored and 

 provisioned, and with the proper complement of coals on 

 board with the poop and forecastle water-tight and assist- 

 ing stability. The curve /' refers to the ship under the 

 same conditions, except that the poop and forecastle are 

 supposed to be so damaged as not to assist stability. It 

 will be observed that although Mr. Barnes considered 



' Publish«3 by Collins, Sons, and Co., in the "Advanced Science Series." 



