April 8, 1909J 



NA TURE 



17: 



An interesting paper was contributed by Prof. J. B. 

 Henderson on the elasticity of ships as deduced from 

 experiments on the vibration of dynamical models. A 

 dynamical model of the ship is constructed out of a bar 

 of steel of uniform thickness and varying breadth, and is 

 loaded with lead weights soldered on. The conditions are 

 that the model must have a load curve similar to the load 

 curve of the ship, and also a curve of moments of inertia 

 of cru-s-scctions about the neutral axis similar to the 

 corresponding curves for the ship. The scale for the load 

 curve need not be the same as that for the moment-of- 

 inertia curve. The model has its frequency measured 

 slroboscopically when supported at two nodes, the vibra- 

 tions being maintained electromagnetically. Experiments 

 have been made at the Royal Naval College, Greenwich, 

 on models representing H.M.S. Pathfinder and the 

 Lusitaiiia, giving results for Young's modulus of 

 21,000,000 lb. and 23,000,000 lb. per square inch respec- 

 tively for these ships. The method seems likely to be 

 useful in dealing with other forms of riveted structures, 

 such as bridges. Prof. Henderson also showed in his 

 paper how the causes of vibration in a ship may be 

 located from an analysis of the pallograph record, and 

 applied the method to the records of the Lusitania and 

 Mauritania. It must, of course, be understood that no 

 criticism is being directed at special vibration in either of 

 the last-mentioned vessels. 



Some useful information on the applications of the 

 internal-combustion engine to marine propulsion was 

 given in two papers, one by Mr. H. C. Anstev and the 

 other by Mr. F. R. S. Bircham, the latter having special 

 reference to submarines. Mr. .Anstey deals with questions 

 of economy of fuel, weight, and space, and, using certain 

 data, estimates that with powers of, say, 500 horse-power 

 on one shaft, it seems reasonable to expect 12 horse-power 

 to 15 horse-power per ton of machinery weight for a 

 complete installation of oil engines n-ithout auxiliaries. 

 The weights would be greater with gas engines on account 

 of the necessity for installing gas producers. The author 

 also deals with a method of splitting the power into a 

 number of convenient units, and transmitting the energy 

 to the propeller electrically. This method has not com- 

 mercial .advantages sufficient to warrant its use for mercan- 

 tile work, and for naval work could not compete with 

 existing machinery in the considerations of weight and 

 space. Mr. Anstey considers that the installing of internal- 

 combustion engines would, in general, save space, but no 

 great saving in weight would result. The difficulties of 

 producing very large gas engines of a type trustworthy 

 enough for marine purposes were pointed out by Prof. 

 B._ Hopkinson, who referred especially to the difficulty of 

 ■efficiently keeping large cylinders cool. The Marquis of 

 Graham gave an interesting illustration of a vessel in 

 which he had the reciprocating engines taken out and 

 ^as engines and producers substituted. He was satisfied 

 with the trustworthiness of the new plant, and found 

 that the radius of action of the vessel was doubled, on 

 account of the lower fuel consumption per horse-power. 

 The total horse-power In this instance was about 500. Sir 

 Wm. White thought that progress in this matter must be 

 gradual, and deprecated the popular exaggeration of the 

 size of engine which could be installed. 



Mr. Bircham discussed the advantages and disadvantages 

 of the system of propulsion for submarines in which 

 Internal-combustion engines are used when on the surface 

 and electric power when submerged. In Del Proposto's 

 alternative method, one cylinder of a four-cycle four- 

 cylinder Diesel engine is used as an air compressor when 

 running on the surface in order to charge storage bottles 

 to a high pressure, the remaining cylinders propelling the. 

 boat and driving the compressor. When submerged, this' 

 cylinder is used as an air engine, exhausting Into the boat 

 ^nd keeping the air therein fresh. In Mr. Bircham 's 

 modification of this plan the internal-combustion engine is 

 couphd to a multi-stage compressor, which Is run as an 

 air entjine of the multi-expansion type when the boat is 

 subnifrged ; the exhaust is used by the internal-combustion 

 engine, a part being turned into the boat to renew the 

 air therein when required. Efficient cooling of cverv part 

 of the intprnal-combustion engine is necessary, the cylinders 

 Ving entirely jacketed and the exhaust pipes water-cooled | 

 NO. 2058, VOL. 80] 



to the boat's skin. This paper is illustrated with several 

 working sections of engines suitable for submarine pro- 

 pulsion. 



Lieut. -Colonel G. Rota, R.I.N., described some trials 

 which he has made on a steamer in the Royal Dockyard 

 at Castellammare di Stabia, first with a single screw and 

 afterwards with two contrary turning screws of different 

 diameters on a common axis and having a constant pitch, 

 and also with another pair having increasing pitch in 

 accordance with Prof. Greenhill's rules given in 1888. 

 One of the propeller shafts was tubular, the other 

 rotating inside the first, both driven in opposite directions 

 from an ordinary reciprocating engine. The author of the 

 paper found that a reduction of power required to main- 

 tain the same speed was obtained of from 30'5 per cent, to 

 26-8 per cent, for speeds of from 5 to 7 knots respectively, 

 the comparison being between double propellers of constant 

 pitch and a single-screw propeller. The gain with double 

 propellers of increasing pitch at the same speeds amounted 

 to 23-8 per cent, and 17-3 per cent, as compared with 

 that required with a single propeller in use. The experi- 

 mental vessel had a length of 4b feet, a breadth of 11 feet 

 g inches, and a displacement of 25 tons. The gain is 

 evidently due to the better guiding of the stream of water 

 reaching the propellers, which are of smaller diameter 

 when double than that required for a single propeller ; the 

 gain in wake is considerable. In this respect the effect of 

 the fore propeller, acting as a guide to the water on its 

 way to the after propeller, may be compared with that 

 of the fixed guide-blades of a steam or hydraulic turbine. 

 The author also points out the adaptability of turbines for 

 driving the shafts, and thus dispensing with gearing ; a 

 special turbine for reversing would also not be required. 



.A note on a mechanical method for determining the 

 thrust of propellers was contributed by Mr. J. H. Heck. 

 In this method one of the tunnel shafts is utilised to 

 form the ram of a hydraulic press, and a slight separa- 

 tion is allowed between two of the tunnel-shaft flanges, 

 these being enclosed within a hollow cylindrical casing in 

 which the shafting can revolve. The casing is fixed in 

 the tunnel, and is made water-tight by means of stuffing- 

 boxes. Water is supplied to the casing by means of a 

 small force pump, and its pressure is indicated by a 

 pressure gauge or recorder. On pressure being applied by 

 means of the pump, the propeller shaft will be slightly 

 forced out of the casing, and, on releasing the pressure, 

 the thrust of the propeller will push it in again. The 

 mean of the gauge readings during both movements of 

 the shaft is taken in order to eliminate frictlonal effects. 

 This mean pressure, when multiplied by the cross-sectional 

 area of the shaft at the place where it is revolving in the 

 stuffing-box, will give the total thrust of the propeller. 

 The author describes some experiments made with this 

 apparatus. 



The offer made by Mr. \. F. Yarrow a year ago to 

 defray the cost, up to 20,000/., of establishing an experi- 

 mental tank at the National Physical Laboratory will be 

 remembered, and the report of the experimental tank com- 

 mittee is of interest. A building subcommittee has been 

 at work, the members being Sir Wm. White, Mr. R. E. 

 Froude, Dr. Glazebrook, and Mr. W. J. Luke. At pre- 

 sent 1240Z. out of the guarantee fund of 2000/. per annum 

 required for maintenance under the terms of Mr. Yarrow's 

 offer has been secured, and it is hoped that the total 

 amount will be shortly made up. Meanwhile, in order to 

 avoid delay, the executive committee of the National 

 Physical Laboratory has guaranteed 800/. per annum, 

 and has entrusted Messrs. Mott and Hay with the pre- 

 paration of plans. The committee has considered the 

 question of the management of the tank, and proposes an 

 advisory committee, appointed by the governing body of 

 the National Physical Laboratory, consisting mainly of 

 representatives of the Institution of Naval Architects. 

 Steps will be taken to preserve the confidential character 

 of all work done at the tank for private firms, as well 

 as the arrangements for problems of general interest to 

 be taken up, and the publication of the results of these 

 Dr. Glazebrook has visited the most recent establishments 

 of the kind in this country, and also in France and 

 Germany, and the results of his visits of inspection are 

 included in the report. The suggested dimensions of the 



