108 EKMAN. ON DEAD-WATER. [norw. POL. EXP. 



two .Fram-models, was dragged through the tank by means of a constant 

 towing weight. When it had gone half the length of the tank or more, I 

 simply took the towing-string with my fingers, and held it steadily slack. 

 The results of these experiments were, on the whole, in accordance with the 

 above mentioned observations; in homogeneous water the boat stopped 

 gradually, moving some boat-lengths, after the towing-string had been slack- 

 ened, while in "dead-water" it moved only a few centimetres. In the latter 

 case the motion was furthermore not constantly the same; sometimes the 

 boat stopped short, sometimes it lost its speed more gradually, and then 

 began to sway several times, first forwards and then backwards, as the 

 waves passed it; sometimes the motion was modified in other ways. 



The explanation of the phenomenon is quite simple with the help of a 

 concrete case. Imagine the Fram moving, first under ordinary circumstances 

 and in another case in dead-water. As will be mentioned in the next section 

 of this chapter, the propelling force of her engine is about 1000 kgr. (or more 

 correctly 1000 g kgr. X cnl - X second ~ 2 , g being the acceleration due to 

 gravity); this is therefore, in both cases, the resistance experienced by the 

 vessel when moving at full pressure. Her inertia is about 1000000 kgr., 

 when the influence of the surrounding mass of water is taken into account 

 (see the next section of this chapter). When the engine is stopped, the 

 resistance is the only force influencing the vessel; she will therefore have a 

 retardation of 1000 gl 1000000= 1 cm. X second ~ 2 . I. e.\ in each second, 

 her velocity will be diminished by 1 cm. / second. Under ordinary circum- 

 stances (in homogeneous water) the Fram had a speed of at least 4 knots, 

 or 200 cm. / second. If her resistance were invariably 1 000 kgr., this speed 

 would then be completely lost in 200 seconds, and the space covered by the 

 vessel in this time would be 20000 cm. or 200 m. The resistance in reality 

 decreases very nearly as the square of the velocity; and supposing this law 

 to be exact, it would be found that 200 seconds after the engine had stopped, 

 the vessel would still have half her original velocity and would have in the 

 meantime moved 277 m. In dead-water, her speed was about l - 2 knots, or 

 only 60 cm. / second. The retarding force is, however, the same as in the 

 former case; the ship would therefore lose her speed in 60 seconds, and in 

 this time she would have moved only 1800 cm. or half a ship's-length. It 

 must be remarked, that in this case, in opposition to the former case, the 



