184 



THEORY OF SEAKEEPING 



f*- 5chwebung = 83.5 sek"*"! 



20 40 eO 80 100 120 140 160 180 200 



Sek 



51 

 41 

 31 

 21 

 II _ 



'0.3m/sek^ f*" 

 Null 



Tauchbeschleunigung 

 -T = 63.5sek H / (von oben) 



Cq) Bac 



bmax=5-"'m/sek^ = lG.3m Umkehrbeschleumgung 



= 0.1 m/ssk^ 

 ,Null 



(b) Drehpunkt 



H T = 83.5- 



"1 



t'max-0-35m/sek'==2.5m 

 (.2.5m) 



21 



(C) Poop bmQx = 4.em/sek = 11.9m 

 _i I 1- 



14 E 26 



20 40 60 60 100 120 140 IGO 160 200 



Sek 



Fig. 22 Curves of vertical accelerations observed at bow, amid- 

 ships, and at stern of SS Hamburg in waves reaching maximum 

 heights of 6 m. Ship's double amplitude of pitching about 12 

 deg (from Kempf and Hoppe, 1926<r). Uppermost part of 

 figure is a typical strain diagram 



Mostly standard ship equipment was used. Only three 

 pieces of special portable instrumentation were in- 

 troduced; namely, an anemometer, an apparatus for 

 measuring roll angles by sighting on the horizon, and a 

 long-period pendulum for measuring pitch angles. Xo 

 description of the latter was given, but it apparently 

 consisted of a suitable recording-pen device and a heavv 

 flywheel having a slightly eccentric suspension. The 

 pitch angle, therefore, was the only continuously re- 

 corded characteristic. Wave data were obtainetl \'is- 

 ually, and periods of wave encounter were measured by 

 a stop watch. The mean of about fi\'e consecuti\-e 

 wa\-es was taken and the observations were repeated 

 three or four times. 



The ships were ecjuipped with logs for speed measure- 

 ments, and all l)ut one were etjuipped with torque meters 

 on the propeller shafts. The only ship without a 

 torcjue meter was run by a reciprocating engine, the 

 power of which was estimated from indicator cards. 



Only a small part of the collected material was pre- 

 sented in Kent's papers. This is also true of practically 

 all the other papers which will be discussed later. It 

 is almost impossible to analyze and to report in a paper 

 of practical length all of the material which can be col- 



t 



Schiffslonge = I93rn 



--ez'o'^ >j* iio'o' 



.DrehachsG 



— ni-r— ^ 



— "T~ **^- 33--»Js+ampfwinkel kl6-J ~-^=^- 



U- 80 



^ S+ampfwinkel 



- 93 



Grenilage? 



.^, Grenzlaqe I 



Grenzlage 1 



Grenzlage 2 



Fig. 2 3 Maximum pitching and heaving of SS Hamburg under 



wave conditions described in Fig. 22. These waves and ship 



motions caused a reduction of speed from 16.35 to 12 knots 



(from Kempf and Hoppe, 1926) 



lected on a single voyage. In the two papers by Kent 

 (1924, 1927a) tables of weather conditions, of ship 

 motions, of rudder motions and of power consumption 

 were gi\'en separately. Different record numbers often 

 are used in compiling different tables, so that it is dif- 

 ficult for a reader to build a comprehensi\'e picture of 

 ship behavior, J. L. Kent's own interpretations and 

 comments are probalily the most valuable part of these 

 papers. The experience gained by Kent on these six 

 \'oyages was reflected in all subsequent papers listed 

 under his name in the l)ibliography of this monograph. 

 The latest published work (Kent, 1950) is a compre- 

 hensive summary based on these voyages, on many 

 towing-tank tests in waves, and on the elementary 

 theory of oscillations. 



Kent's description of sea wa\'es emphasized the irregu- 

 larity of the sea, but his final data were given in terms 

 of average wave length, height and period. Ship oscil- 

 lations in pitch and in roll were shown to increase to 

 maximum and then to decrease with a certain degree of 

 regularity. Kent listed the number of individual oscil- 

 lations between periodicall.y occurring high motion 

 amplitudes. This characteristic also was reported by 

 Kempf and Hoppe (1926) who observed that the 

 passenger liner Hamburg had its maxima of pitching 

 amplitude at about 80-sec intervals. These "beats" 



