38 



EKMAN. ON DEAD-WATER. 



NORW. POL. EXP. 



B. RESISTANCE TO VESSELS IN SHALLOW WATER. 



The general principles explained in the preceding section are quite in- 

 dependent of whether the vessel is moving in deep water or in shallow water; 

 hut nevertheless the law connecting velocity and resistance is essentially dif- 

 ferent in the two cases. 



This subject, investigated more than 60 years ago in a number of canals 

 in Scotland, is of great interest to us, because it offers a remarkable analogy 

 to the laws of resistance in "dead-water". Scott Russell describes in the 

 following manner the discovery of the peculiar fact which induced further in- 

 vestigations upon the matter. 1 



"As far as I am able to learn the isolated fact was discovered accidentally on the 

 Glasgow and Ardrossan Canal of small dimensions. A spirited horse in the boat of William 

 Houston, Esq., one of the proprietors of the works, took fright and ran off, dragging the 

 boat with it; and it was then observed, to Mr. Housron's astonishment, that the foaming 

 stern surge which used to devastate the banks had ceased, and the vessel was carried on 

 through water compaiatively smooth, with a resistance very greatly diminished. Mr. Hou- 

 ston had the tact to perceive the mercantile value of this fact to the Canal Company, with 

 which he was connected, and devoted himself to introducing on that canal vessels moving 

 with this high velocity. The result of this improvement was so valuable from a mercantile 

 point of view, as to bring, from the conveyance of passengers at high velocity, a large in- 

 crease of revenue to the Canal proprietors. The passengers and luggage are conveyed 

 in light boats, about sixty feet long and 6 feet wide, made of thin sheet-iron, and drawn by 

 a pair of horses. The boat starts at a slow velocity behind the wave, and at a given signal 

 it is by a sudden jerk of the horses drawn up on the top of the wave, where it moves 

 with diminished resistance, at a rate of 7, 8 or 9 miles an hour." 



Scott Russell was appointed 

 to investigate the matter and ar- 

 ranged great experiments 1 with 

 vessels 10—20 m. in length and 

 weighing 600—9000 kgr. Fig. 4, 

 reproduced from Scott Russell's 

 paper, represents the resistance 

 at different velocities according to 

 these experiments. The velocities 

 are plotted along the horizontal Y- 

 axis in statute miles 2 an hour, and 



3 8 4367891011 12 13 14 \i IS 7 13 1 



Fig. 4. 



1 John Scott Russell, "Experimental Researches into the Laws of Certain Hydrodyna- 

 mical Phenomena that accompany the Motion of Floating Bodies, and have not pre- 

 viously been reduced into conformity with the known Laws of the Resistance of Fluids". 

 Trans, of the Roy. Soc. of Edinburgh. Vol. XIV, 1810. 



2 One statute mile is 1609 m. 



