July 27, 1905] 



NA TURE 



305 



over all the humps at about 25 knots, where there is a 

 range of about 200 horse-power. The curve for 90 feet of 

 water is, however, for 5000 horse-power at 26 feet, or 

 about 500 horse-power above the next highest curve. It 

 would therefore pay better, according to these model ex- 

 periments, to run a 26-knot trial of a destroyer in a depth 

 of 20 feet to 60 feet rather than at a depth of 90 feet ; the 

 saving in power for the given speed due to the use of 

 shallower water would be about 600 to 700 horse-power. 



We have been obliged to depart from the text of Mr. 

 Harold "^'arrow's paper in order to give the facts con- 

 tained in his diagram. Limits of space prevent detailed 

 reference to other particulars brought forward by these 

 suggestive trials, but enough has doubtless been said to 

 show their interest and the wide field for further investi- 

 gation that is afforded by the numerical data now at 

 command. It will be remembered, as Mr. Harold Yarrow 

 pointed out, that the tank experiments were made in the 

 usual way without propellers, and this would doubtless 

 have a considerable influence on the results ; but possibly 

 a way may be found, as suggested by Sir William White, 

 to add the propeller, and so bring the tank conditions 

 more nearly akin to actual practice. It will be remembered 

 that the late Mr. Froude proposed to run a propeller, 

 worked by independent mechanism, at a speed of revolu- 

 tions corresponding to that of actual practice, the model, 

 of course, being towed by the carriage. 



Mr. Marriner's investigation of the model results showed 

 that they should,, as Mr. Harold Yarrow said, " be 

 accepted with caution." In order to check these tank 

 data progressive trials were made with an actual destroyer 

 on a carefully selected course off the mouth of the Thames. 

 Four tugs were anchored to mark the course, which 

 extended from the East Girdler buoy across the Tongue 

 Sand to a point east of the extreme north-east point of 

 the Tongue Spit. This gave water of depths varying 

 between about 14 to 16 feet over the sand, and 100 to 

 102 feet in the Queen's Channel. The revolutions of the 

 engines, the fore and aft inclination of the vessel, and 

 the height of the stern wave were noted, indicator 

 diagrams also being taken. The data thus obtained at 

 varying mean speeds were given by means of diagrams 

 thrown on the screen. We have not space to repeat all 

 the records, but will take as an example the run made 

 at a mean speed of about 22-2 knots, the steam pressure 

 being 140 lb. In running from rather less than 50 feet 

 depth into water of 20 feet, the revolutions increased from 

 about 305 to more than 325 ; the inclination in a length of 

 20 feet decreased from approximately 55 inches to 45 or 

 4^ inches ; and the approximate height of the stern wave 

 fell from 20 inches above the deck level to a little more 

 than 10 inches below the deck level, or about 2 feet 

 6 inches. Naturally any increase or reduction of resist- 

 ance to the vessel would be accompanied by increase or 

 reduction in the rate of revolutions of the engine, the 

 steam pressure being constant. Increased height of stern 

 wave and greater inclination are also signs of increased 

 resistance and a greater demand for horse-power. 



It would be difficult to deal adequately with Mr. 

 Marriner's paper within anything approaching the space 

 we have at our disposal, and without the diagrams by 

 which it was accompanied. We can only hope, therefore, 

 to give an idea of its scope, and refer our readers to the 

 original in the published Transactions of the institution. 

 The contribution consisted of a discussion, on a scientific 

 basis, of the results contained in the preceding paper, 

 the size of waves made by a vessel in her passage being 

 a measure of the power absorbed in their formation. 

 .'\s the height of the stern wave was seen to increase 

 when the resistance of the ship increased abnormally, it 

 was to be assumed that anything which tended to retard 

 the formation of waves would reduce the loss from wave 

 making. The author cited the work of W'. Froude and 

 his son, R. E. Froude, of Lord Kelvin, D. W. Taylor, of 

 the LTnited States Navy, and Prof. Horace Lamb. The 

 formula for relation of length to speed of ordinary re- 

 peating waves in deep water was set forth, and also the 

 more complicated equation for shallow water. The equa- 

 tion showing critical depth for speed and critical speed for 

 depth w-as given, and the conclusion was drawn (sup- 

 ported bv Scott Russell's equation for the solitary wave 



NO. 1S65, VOL, 72] 



in canals) that " the wave at the critical speed changes 

 from the repeating to something approaching the solitary 

 type." 



The author next considered the waves accompanying the 

 vessel. Transverse waves should tend to become longer 

 and longer for the same speed as the depth diminishes 

 until, at the critical depth, these should be of the isolated 

 type. In shallower water, past the critical depth, there 

 would be no transverse wave corresponding to the critical 

 depth. Actually as the waves became longer if they did 

 not lengthen as rapidly as investigation would lead one to 

 suppose they would be travelling faster than their natural 

 speed, and must be dragged by the boat. The increased 

 resistance on approaching humps in the curve supports this 

 view. The isolated wave is non-repeating, and exists 

 only under certain relations of depth to speed. After pass- 

 ing the critical point the transverse wave disappears, being 

 replaced bv confused water. The paper was accompanied 

 by diagrams illustrating these points, and it was considered 

 a fair deduction that the waves formed by a ship closely 

 follow the laws of waves in open water. The effect of 

 the vertical sides of a canal in diminishing the loss of 

 energv was pointed out bv the author, and the manner in 

 which the restricted width of a tank might have a similar 

 effect was noted. The interference of the bow-wave system 

 on the stern-wave system was discussed, it being shown 

 that the union of the bow and stern waves (the crests 

 coinciding) resulted in a large resultant wave which 

 would carry away a great deal of energy. The velocity 

 of diverging waves is much less than the speed of the 

 vessel, speeds attained up to the present not being high 

 enough for waves to approach the critical speeds for the 

 depths in which vessels usually run. Diverging waves 

 apparently constitute the principal wave-making resistance 

 at speeds beyond the critical combinations of depths and 

 speeds under consideration. The final conclusions of the 

 author were as follows :—" (1) The critical combinations 

 of depth and speed do not depend on the size of the vessel. 

 (2) Of these critical combinations there is, for every vessel, 

 one more serious than the others, and where this worst 

 combination occurs depends largely on the length of the 

 vessel. (3I The depth to be a%-oided is given by the 

 equation d = V=/io, and the resistance diminishes in both 

 greater and lesser depths. The further away from this 

 bad depth the better, especially on the deep side." 



In the course of the discussion which followed the read- 

 ing of these papers, Mr. A. F. Yarrow, in conformity with 

 a suggestion made by Sir William White, proposed, and 

 Mr. S. W. Barnaby seconded, a resolution that the 

 ."Vdmiralty be urged to' erect a measured mile, where ample 

 depth might be found, in proximity to Chatham and the 

 Thames. This resolution was put to the meeting by Sir 

 John Durston, who occupied the chair, and was carried 

 unanimously. It was but the logical outcome of the facts 

 brought forward. The measured mile in the_ Clyde at 

 Skelmorlie has ample depth of water, and is, as Sir 

 William White said, the only satisfactory mile for high- 

 speed trials; a fact which, it is acknowledged, gives the 

 ship-builders of that district a manifest advantage over 

 those of other centres. Mr. Barnaby stated that when a 

 destroyer built bv his firm, John I. Thornycroft and Co., 

 was tried on the Skelmorlie mile an increase of speed 

 of I knot was obtained over that reached under the best 

 conditions on the Maplin mile, whilst an increase of 

 3 knots was reached as compared to running on the 

 Maplin when the state of the tide was most unfavourable. 

 Sir William White, in a letter to the secretary, read at 

 the meeting, heartilv endorsed the suggestion of a deep- 

 water measured mile off the Thames. He also pomted 

 out, with great regret, that it was necessary for Messrs. 

 Yarrow to go to Germany for their tank experiments, and 

 trusted that the fact rnight furnish a fresh incentive 

 towards the establishment of a research tank at the 

 National Physical Laboratory. 



In the discussion on the technical details of the two 

 papers, besides those mentioned, Mr. J. H. Narbeth, of 

 the Admiraltv, Mr. R. Saxton White, Captain Jackson, 

 R.N., Controller of the Navy, Mr. W. H. Whiting, chief 

 constructor, and Prof. Biles took part. Generally it may 

 be said the views expressed by the authors were not dis- 

 puted, although Sir William White did not quite agree 



