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



get a dead-water resistance of 2*72 gr. ; while experiment 83 gave a maximum 

 resistance of 2 - 25 gr. at 10'6 cm./second and a dead-water resistance of 

 2 - 25 — 043 = 1*82 gr. only. It is not probable that the maximum dead-water 

 resistance at steady speed should be smaller than the greatest dead-water 

 resistance in an experiment such as 82; and it might consequently be expected 

 to be 50 per cent greater than the maximum dead-water resistance according 

 to our definition, or even more. In open water, where the waves spread more, 

 to the sides, the difference may however, be smaller (compare p. 73). 



The above-mentioned attempts to give to the boat a more uniform motion 

 (pp. 89 — 90), were then, for one more reason unsuitable. For if the towing 

 force be increased gradually during the course of the experiment, the maxi- 

 mum resistance obtained, will have another, not definable, value between the 

 maximum resistances according to the two before mentioned definitions. 



To determine a few points on the resistance-curve between the maximum- 

 resistance and minimum-resistance points a starting force greater than the 

 maximum resistance was used, and an attempt made to remove it when the 

 resistance was diminishing and just equal to the constant towing force (see for 

 example experiment 84). If the velocity was retarded, or continued to be 

 accelerated after the starting weight was lifted off, a corresponding correction 

 was applied to the resistance. It is apparent that these measurements could 

 not be but rough approximations, for the motion will be influenced by the 

 waves just before generated at a lower speed. They establish however, the 

 continuity of the resistance-curve and give an idea of its shape. Wilh regard 

 to the part of the resistance-curve beyond the minimum-resistance point, the 

 measurements are still more unreliable. I have for this part of the curve 

 supposed that the resistance is very nearly the same as in homogeneous water. 



At the time of the experiments, I did not pay much attention to the 

 temperature of the water; and in the following applications I have for the 



sake of simplity assumed the specific gravity S tfs of the fresh-water to be 1. 



As the temperature in most cases, was below 15°, the differences of specific 

 gravity between fresh-water and salt-water, were as a rule, somewhat smaller 

 than here given, sometimes by more than - 0005. 



