S6S 



NA rURE 



[April i i, 1895 



THE I.XSTITUTION OF NAVAL 



ARCHITECTS. 



'T'HE annual spring meeting of the Institution of Naval 

 ■*■ Architects was held on Wednesday, Thursday, and Friday 

 ■of last week, in the theatre of the Society of Aits. There was 

 a long list of papers set down for reading and discussion as 

 follows : — 



"Noies on further Experience with first-class Battle-ships," 

 by Sir William White, Director of Naval Construction. 



" The Elements ol Force in a Warship," by Vice- Admiral 

 P. H. Colomb. 



"On Steam Pipes," by J. T. Milton, Chief Engineer Sur- 

 veynr. Llo)Hs' Retjistry of Shipping. 



" Light Draught River Steamtrs," by George Rickard. 

 " On solid Stream Forms and the Depth ol Water necessary 

 to avoid abnormal Resistance of Ships," by D. W. Taylor, 

 Senior Assistant to Chief Constructor of U.S. Navy. 



" On the Method of initial Condensation and Heat W'aste in 

 Steam Engine Cylinders," by Prof. R. H. Thurston, Sibley 

 Collrge, Cornell University, New York. 



" De-cripiion of an Aluminium Torpedo Boat built for the 

 French Government," by A. F. Yarrow. 



"On Vibrations of Higher Order in Steamers, and on 

 Torsional Vibrations," by Otto Schlick. 



" On the Vibrations of Ships and Engines," by W. Malloek. 

 "On a Method of Extinguishing Vibrations in Marine 

 Engines," by Mark Robinson and H. Riail Sankey, Captain 

 (retired) R.E. 



"On the Transverse Stability of Floating Vessels containing 

 Liquids, wiih special Reference to Ships carrying Oil in Bulk," 

 by W. Hok. 



" Induced Draught as a Means for developing the Power of 

 Marin- Boilers," by W. A. .Martin. 



Alter the usual formal proceedings had been transacted, and 

 the President, Lord Brassey, had given a brief address. Sir 

 William White's paper w.is read by his colleague at the 

 Adojiralty, Mr. W. E. Smith, the author being absent owing 

 to serious illness ; from which, every one will be glad to hear, 

 he appears in a lair way of recovery. This contribution dealt 

 chiefly, indied almost wholly, with the question of steadiness 

 in the laige ba' tie ships of the Royal Soverri^n c'ass, and 

 the effect of fitting them with bilge keels. This paper may 

 be said to he the complement of another memoir by the 

 same author, read befire the Institution last year, in 

 which the experience gained with the big line of battle- 

 ships was recortled. Win n the Royal So-uerngn was designed, 

 it was thought th.it the period of oscillation would approximate 

 to that of the Inconstant, Herctila, and Sultan, which were all 

 remarkalily steady ships. Tiie Hercules and Sultan had only 

 shallow side keels from 9 to 10 inches deep. It was thought 

 that the great inertia due to the large dimensions of the new 

 ^hips would lender them so sttady that these small bilge k- els 

 might be omitted. That the expeclaions formed in this respect 

 have not been fulfillid, shows that even the best-informed naval 

 archiiecis, even when supported by the best scientific evidence 

 at their command, may l)e wrong at times. The performance 

 of the ships of the Royal Sovereign class at sea led to the fiiting 

 of bilge keels to oi.e ot them — the Repulse. These keels are 

 «ach about 200 feci long and j (eet deep. Four of the class 

 were at s-a off ihe west coast ol .Soolland in company. There 

 was a lorg low swell, 300 lo 4C0 feet from crest to crest, and 

 with afxriod of about ten to twelve seconds. The Resolution, 

 without bilge keels, rolled 23, and the Repulse 10. The sea 

 was on the quarter, and the speed such as 10 produce heavy 

 rolling. The iccoids of angle of roll were obtained by ihe 

 pendulum, an in>tiument notoriously untrustworthy, but in the 

 proem case the rtsults quoted wire probably fairly accurate. 

 At any rale, there was noiloubi that the behaviour of the ship 

 was iiomensely improved by the bilge keels, and it was decided 

 10 fit all other shipt ol the class in a similar manner to the 

 Repulse. I he consen-us of ^pinion o( naval oilicers is thai roll- 

 ing has bc<n grratly reduced. Sir William While very frankly 

 admits that the steadying elTect of bilge keels has grei'ly ex- 

 cetded that which wa> anticipated ; and, indeed, the o|jinion of 

 naval architects ai large will now have to be rcvljus el, and 

 the data upon which ship designers work will require lo be 

 modified. Fur scientific pui|>ose« more exact information wai 

 required than could i>c obtained by trials at sea, on which, as is 

 well known, it Is generally imfxissible to obtain accurate records. 



It was therefore arranged that still-water rolling experiments 

 should be made with the sister ships Revenge and Resolution. 

 Mr. R. E. Froude, whose father's work is so well known in this 

 field, had charge of these trials. One series of experiments was 

 made before bilge keels were fitted, and another alter the 

 keels had been attached. Each series was divided into two 

 sections, the ships having a metacentric height of 3} feet 

 in one case, and a little under 4 feet in the other. The 

 conditions approximate to those of maximum and minimum 

 stability on service. The oscillation of the ships was 

 produced by training the heavy guns and running men 

 across the deck in the usual way. The results of these trials 

 were shown by means of diagrams hung on the walls of the 

 theatre. Curves for the older ships Sultan and Inconstant were 

 also placed on the diagram. Starting from an angle of inclin- 

 ation of 12° from the vertical, it was seen that in order to reduce 

 the corresponding inclination of 6°, the Rezenge, without bilge 

 keels, required to make 18 to 20 swings, and the Sultan about 

 17 ; there being a remarkable similarity between the curves of 

 declining angles of the two ships. The Sultan, as already 

 stated, has always been considered a satisfactory vessel in regard 

 to steadiness. Starting from an angle of inclinatiotr ol 6' 

 from the vertical, it required 45 swings in the Acvenge without 

 bilge keels to reduce the corresponding angle ol inclination to 

 2°. After hilge keels were fitted, an equal reduction was 

 obtained by only 8 swings. For the. Sultan and inconstant, 

 32 lo 20 swings respectively would be required to produce the 

 same reduction. Ihe Revenge, before the bilge keels were 

 fitted, could be rolled up to an angle of inclination of 13° to 

 the vcitical by moving her barbette guns. Alter the keels were 

 in place it was dilficull to exceed an inclination to the vertical 

 of 6° to 8°, even with 300 to 400 men running .icross the deck, 

 and acting in c )njunction with the movement of the guns. 



The variation in the periods of swing (from out lo oat) 

 brought to light by these trials are insiructive. Without 

 bilge keels, the author continues, the rolling was practically 

 isochronous at large as well as small angles. The period for a 

 single swing was 76 seconds for maximum stiffness, and 8 

 seconds for minimum stiflness, for large as well as small arcs of 

 oscillation. With bilge keels, within the r.inge of experiment 

 up to a swing of about 12° (6° each side), the period of a single 

 swing decreased as the angle of inclination became smaller; 

 the reduction being about 2^ per cent, in going from a mean 

 inclination to the vertical of 5° to one of 1°. When the meta- 

 centric hcighis and radii of gyration of the ship were appreci- 

 ably unchanged, there was an increase of about 5 per cent, in the ' 

 period due to the action of the bilge keels. 



A study of the action of bilge keels on a chip's performance not 

 only involves questions of the greatest practical importance to 

 the >hip designer, but also problems of high scientific interest. 

 From whichever point of view we consider Sir William White's 

 paper, it is one of exceptional value. It i^ seldom lh.it the 

 naval architect has the opportunity of mnking trials or experi- 

 ments on so grind a scale as that afforded by the big battle- 

 ships of the Royal Sovereign class, and lor this reason we are 

 giving unusual space to this jiaper. Ne\ertheless, we are un- 

 able 10 follow the author in his comparison of the experiments 

 undc' consideration with those jireviously made both by I''rench 

 and English engineers. For the>e we must refer our readers to 

 the original memoir, confining ourselves to the main results, from 

 which a comprehensive view of the scope of the paper may be 

 formed. One of the most impoitant of these results is the 

 increased extinctive effect shown by ttie experiments lo be pro- 

 duced by bilf^c keels when the ship has headway, compared 10 

 ihe elTect when she is not progressing. The experiments under 

 way were limited in number, and, as the author points out, are 

 peih.ips not so definite as those with the .-■hiii not having head- 

 way. " Still they are very suggestive," to once more quote ihe 

 author's woids, "and confirmatory ol the concluson fiom pre- 

 vious experience that the rale of extinction is sensibly increased 

 by headway, the ship eniering uniiislurbed water while oscil- 

 lating, and the inertia ol ihal unoisturbtil water having to he 

 overcome." We can only quote the broad results. Slnrting 

 at 5 from the vertical the angle-, of inclination reached, 

 alter a ceitain number of swing-, were as follows : — Alter 4 

 swings, ro headway 295,81 10 knots 235, at 12 knots 

 22°. After 16 swings, no headway 1'I5', 10 knots ^o", li 1 

 knots '25 . 



It will be remembered by students ol this subject that ihe 

 late Mr. Froude assigned a coelhcient of lesistance of 16 Ibi. 



NO. 1328, VOL. 51] 



