3o6 



NA TURE 



[July 25, 1907 



ing it, is very costly to create and to maintain ; and over 

 and above the cost of construction, and of running it, 

 there is the all-important question of the quality of the 

 results it will produce. It is not enough to procure a tank 

 with all its apparatus and appliances and to attach to it 

 a staff of scientific men to run models and take records of 

 their speed and resistance. The work is of so delicate and 

 intricate a nature that the personal qualities of the ex- 

 perimenters count for very much in it. The results 

 obtained by the late Mr. \V. Froude and the present Mr. 

 R. E. Froude owe much of their value to the exceptional 

 qualifications of those eminent men for scientific research, 

 especially upon the experimental side. It is the men, and 

 not the tools, who constitute the most important factor in 

 work such as this, and the right men for it are very 

 difiicult to obtain and to keep. 



.\n attempt has recently been made to provide an experi- 

 mental tank at the National Physical Laboratory, to be 

 worked by members of the staff there, at which ship 

 models might be tested for resistance, but up to now this 

 has been without result. There is another way of dealing 

 with the matter, however, and a readier one for the ordinary 

 purposes of the ship-designer, which has been initialed by 

 Mr. R. E. Froude, that promises to overcome the difficulty 

 in a satisfactory manner. Mr. Froude read a paper at 

 the Institution of Naval .Architects, three years ago, upon 

 " Some Results of Model Experiments," in which he gave 

 results of a series of general experiments on systematic 

 variations in form of hull, the variations consisting of 

 six different sets of typical lines, varied in proportion by 

 independent variations of length, beam, and draught. The 

 resistance data given by these experiments are published 

 in the paper in such a form that the resistance of a ship 

 of any dimensions, the lines of which are similar to the 

 typical ones, which are also given, can be readily taken 

 out. The types dealt with have block coefficients, or ratios 

 of displaced volume to product of length, breadth, and 

 draught, varying from 0-4865 in the finest to 0541 in the 

 fullest. Now this covers a very important class of mercan- 

 tile steamers — that of fast Channel boats — and the designer 

 of such a boat could have nothing better for his speed 

 calculations than the data in this paper. He has only 

 to refer to Mr. Froude's tables and diagrams in order to 

 determine at once the proportions and form that will best 

 suit the circumstances, and to construct the lines of his 

 boat. 



If similar data could be obtained lor other forms of 

 ships, say for the fasl-liner type, with block coefficients 

 varying from about 0-6 to 0-7, the designer of that class 

 of vessels would indeed have cause to be grateful. The 

 best practical solution of this long-vexed problem of the 

 relation of power to speed appears to be an extension of 

 Mr. Froude's system to vessels of the fast-liner type, and 

 to others with which the ship-designiT ordinarily has to 

 deal, leaving those of abnormal proportions or form, and 

 also the work of general research, to a public experimental 

 tank — if ever we find enterprise enough among those 

 interested to get one set up in this country. 



The resistance of a ship may be estimated to a close 

 degree of accuracy in the manner mentioned, but the 

 determination of the engine power required to overcome 

 that resistance involves the important consideration of 

 screw-propeller efficiency. The problem of the most 

 efficient design of propeller for any given size and form of 

 ship and rate of turning of shaft is as yet far from prac- 

 tical solution. Model experiments have been carried out 

 at Haslar with a large number of propellers of varying 

 pitch, diameter, and developed area, but these model screws 

 have been very small, as the size and speed at which they 

 could be worked were limited by the stresses the experi- 

 mmtal mechanism is capable of bearing. 



Fun her advance might be effected by carrying out 

 experiments on a larger scale than those already made, 

 and with stronger appliances than those now used for 

 the purpose in the .Admiralty tank. .A still more effective 

 means, which I hear is under consideration by Mr. Froude, 

 would be to build an experimental launch for the purpose, 

 to be run in open water and propelled by machinerv of 

 considerable power. The propelling machinery could be 

 so arranged that the thrust of the screws and' the torque 

 on the shaft would be automaticallv recorded, as in the 



NO. 1969, VOL. 76] 



case of tank experiments. With such an arrangement 

 screws up to 3 feet in diameter could be experimented 

 with — a great advance on anything that could be hoped for 

 in the tank — and the important problem of propeller 

 efficiency might thus be brought much nearer to a practical 

 solution. 



We now come to the greatest problem of all with regard 

 to the propulsion of ships, and that is the form which 

 propelling machinery is likely to take in the immediate 

 future. .Already an important change is in progress from 

 the ordinary reciprocating marine engine to the steam 

 turbine, and the question is not only how far that change 

 will extend, but whether the whole of the cumbrous 

 apparatus required for producing steam may not before 

 very long be swept out of mercantile steamers, and the 

 power be obtained from some form of internal-combustion 

 engine. \'ery few ocean steamers have been fitted with 

 turbine machinery or are being so fitted, and although this 

 may not cause surprise in the case of cargo-boats and other 

 vessels of low or even moderate speeds, it may appear 

 strange that liners of high speeds are still being fitted 

 with reciprocating engines, and that the bold lead given 

 by the Cunard Company with their two fastest new boats 

 and the Carmania should not be generally follow-ed. 



The chief reason for hesitation to put turbine machinery 

 into ocean liners is the doubt which exists as to coal con- 

 suiTiption. The amounts at stake are so large in these 

 costly vessels when experiments with novel propelling 

 machinery are tried that everybody prefers to see someone 

 else make them. The Cunard Company is making the 

 crucial experiment upon the largest scale that is now 

 possible, and everyone interested in progress must wish 

 those responsible for it all the success they hope for and 

 deserve ; but the result is to some extent uncertain, and the 

 immediate future of the turbine in fast liners depends 

 greatly upon it. 



In warships the consumption of coal has been brought 

 down to about 1-7 lb. per equivalent I.H.P. of recipro- 

 cating engines per hour, and the same in mercantile 

 boats of cross-Channel type. That is as good as can 

 be obtained 'with reciprocating engines in the same classes 

 of vessels, as weight has to be kept down as much as 

 possible in these by shortening the stroke, and using high 

 mean pressures of steam in the cylinders, in order to get 

 all the power that is practicable out of a moderate size 

 and weight of machinery. It pays better, in these cases, 

 to stop somewhat short of the maximum efficiency that 

 is attainable than to carry the additional weight which the 

 increase would involve. In ocean liners the conditions are 

 different, and economy of consumption is there the chief 

 point aimed at. Their consumption with quadruple- 

 expansion engines and a boiler pressure of 210 lb. to 220 lb. 

 per square inch has been brought down to 1-3 lb. of coal 

 per I.H.P. per hour for all purposes. The substitution of 

 turbines for reciprocating engines in ocean vessels depends 

 chiefly upon whether the consumption with turbines can 

 also be brought down to this low figure, and there is no 

 satisfactory evidence that this is now practicable. It 

 appears probable that the marine turbine may ultimately 

 be so improved ns to beat the best reciprocating engines 

 in economy of consumption in ocean liners, but no proof 

 is forthcoming th.-ii it can yet be relied upon to do it. 



The correct measurement of the power given out by 

 turbine machinery is a practical problem of great import- 

 ance. Considerable success has been achieved with a 

 telephonic recording apparatus for indicating the twist of 

 a shaft over a given length, and thus giving a measure 

 of the torque. The record is not always, however, so 

 definite and accurate as could be desired. A satisfactory 

 solution of this problem is much required by ship designers. 



The question of some form of internal-combustion marine 

 engine suitable for large ocean vessels is still about where 

 it was when Mr. Milton's paper was read and discussed 

 here last January, and I do not feel able to add anything 

 with advantage now to that paper and discussion. I will 

 therefore merely enumerate the conditions, most of which 

 were mentioned by Mr. Milton, that must be satisfied by 

 a successful marine engine of anv type whatever : — 



fO The engine must be reversible. 



(2) It must be capable of being stopped quickly, and of 

 being started quickly either ahead or astern. 



