NATURE 



THURSDAY, SEPTEMBER 13, 1906. 



77//S PHENOMENOX Ol- ■■DEAD-WATER." 

 The Norwegian North Polar Expedition, 1893-6. 

 Scientific Results. Vol. v. On Dead Water. By 

 V. VValfrid Elcman. (London : Longmans, Green 

 and Co., 1906.) Price 20s. net. 



ON August 29, 1893, the Fram was steaming in 

 smooth and open water between tlie isle of 

 Taiinur and -Mmquist Islands; towards evening she 

 approached thick ice in order to make fast to it. A 

 very slight current was observed as she neared the 

 ice, but the vessel made extremely slow progress, and 

 the speed was reduced to i or i^ knots, although the 

 engines were working at full power, which would 

 have given a speed of 4i to 5 knots in ordinary 

 circumstances. Nansen's journal attributed this 

 singular behaviour to the Fram having " got into 

 dcttd-^i'atcr " — a condition which has been frequently 

 met with by ships navigating the Norwegian fiords, 

 and occasionallv encountered elsewhere. Nansen con- 

 sulted Prof. Bjerknes (in 1898) on the subject, and 

 th;it gentleman suggested the explanation that " in 

 the case of a layer of fresh water resting on the top 

 of salt water, a ship will not only produce the ordinary 

 \\a\.s at the boundary between the air and the 

 water, but will also generate invisible waves in the 

 boundary between salt water and fresh water; . . . 

 the great resistance experienced by the ship being due 

 to the work done in generating these invisible waves." 

 After some discussion between Nansen and Bjerknes 

 it was decided to make a rigorous experimental in- 

 vestigation ; the work was entrusted to Dr. Ekman 

 (assistant in the Central Laboratory for the Inter- 

 national Study of the Sea at Christiania). Its history 

 :ind results are recorded in the remarkable memoir 

 under review, which occupies the greater part of the 

 volume in which it appears, and forms an important 

 it'm in the scientific results of the North Polar Ex- 

 pedition. 



Dr. Ekman 's memoir must be closely studied before 

 its full merits can be appreciated. It contains an 

 excellent summary of the present state of knowledge 

 in regard to the resistance offered by water to the 

 motions of ships, and deals in great detail with the 

 wave-phenomena attending these motions through 

 homogeneous fluids and through layers of different 

 densities. The mathematical and experimental works 

 of Scott Russell, W. Froude, Stokes, and Lamb are 

 laid under contribution, and it is demonstrated that 

 Prof. Bjerknes's suggestion furnishes a reasonable 

 explanation of the phenomena of "dead-water." A 

 great body of testimony regarding these phenomena 

 is brought together from logs, journals, and letters 

 of experienced seamen, who confirm the observation 

 made by Nansen in the Fram, viz. that ships 

 encountering a la\-er of fresh water or brackish water 

 superposed on sea water of greater density do experi- 

 ence greatly increased resistance, lose in speed, and 

 not infrequently become unhandy, not answering their 

 li:lm. These results obtain when vessels are moving 

 at very low speeds before they " get into dead-water " ; 

 NO. 1924, VOL. 74] 



they are much more frequently seen in sailing vessels 

 than in steamers, and occur in the estuaries of 

 rivers, straits, fiords, or other situations where fresh 

 water accumulates. Sometimes ships get into dead- 

 water when considerable currents arc seen on the 

 surface ; at other times there is little or no current. 

 In some cases the depth of fresh or brackish water 

 has been less than the draught of the ship, and in 

 others greater. Ships get into dead-water suddenly, 

 and may become free again as suddenly. Any change 

 of condition in the surrounding water, such as the 

 passage of another vessel near the ship " in dead- 

 water," or a sudden alteration in the speed of a ship, 

 tends to destroy the "drag" of dead-water and to 

 set the vessel free. Steamships possessing capacity 

 for high speed may get into dead-water when moving 

 very slowly, but have no difliculty in freeing them- 

 selves by using the engine-power in reserve. .Sailing 

 ships, or auxiliary steamships like the Fram, have not 

 the same command of speed. It will be seen, there- 

 fore, that the elucidation of the problem has scientific 

 rather than practical interest, but from the scientific 

 side the experiments of Dr. Ekman deserve and will 

 receive close study by all interested in ship propulsion 

 and hydrodynamics. The experiments were neces- 

 sarily made on a small scale, the larger model ships 

 used being only one-hundredth of the full size 

 (i : 100). Dr. Ekman acknowledges the drawbacks 

 unavoidable with such small models, and there is no 

 need to dwell further upon the point ; but great interest 

 would attach to the performance of experiments of a 

 similar character on a larger scale in experimental 

 tanks now existing in this country and abroad, where- 

 in the methods introduced by William Froude are 

 followed and developed. 



One cannot speak too highly of the extreme 

 ingenuity and care bestowed by Dr. Ekman on these 

 experiments, their numerical and photographic re- 

 cords, and the detailed analysis of results. The illus- 

 trative diagrams appended to the memoir are valuable 

 and suggestive, and the broad conclusions reached 

 command acceptance. A singularly close agreement 

 is reached between the experimental results obtained 

 with models and the observations made by Nansen in 

 the Fram. The enormously increased resistance and 

 loss of speed are shown to be fully accounted for by 

 the energy expended in forming an invisible wave 

 series at the boundary of fresh and sea water. This 

 would hardly appear probable at a first glance. Sup- 

 posing the speed of the Fram to have been diminished 

 from 45 to 15 knots, the resistance at the lower speed 

 in dead-water must have been about nine times as 

 great as that when the Fram moved at the same speed 

 in sea water of considerable depth. In the latter 

 circumstances it is well known that nearly the whole 

 resistance would be accounted for by friction of water 

 against the bottom, and a very small part by wave 

 making, as there would be little surface disturbance 

 at so low a speed. These considerations make the 

 results obtained by Dr. Ekman the more remarkable, 

 and it is worth notice that even when a ship is " in 

 dead-water " the disturbance of the upper surface 

 may be very small, although that at the boundary 



