414 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 61.20 



in Sec. 35.12, is estimated by methods derived 

 from model tests [EMB Rep. 189, Mar 1928]. 



It is shown in the references cited that the 

 augmented lock resistance 72i may be related to 

 the open-water resistance Ra by the equation 



— 1 = kn 



(61. iv) 



where n is the ratio of the maximum-section area 

 Ax to the transverse clearance area between the 

 ship ma.ximum section and the lock boundaries. 

 The coefficient fc is a number which has been 

 foimd by experiment to vary from 6.2 to 20 and 

 over but whose average value may be taken as 

 about 11. Eq. (61.iv), shown graphically in 

 Fig. 6 LP, should predict Rl/Ro within plus and 



Resistance 



Fig. 61. P Graph for Determining Added Resist- 

 ance OF Ships When Transiting Canal Locks 



minus 25 per cent for entrance and exit speeds 

 not exceeding 3 kt, as apphed to ships having 

 lengths of 600 ft or more. The model tests covered 

 ranges of n from about 0.2 or less to 2.82. It is 

 perfectly feasible, however, to transit ships with 

 clearances so small that n is approximately 8 

 to 10. 



6L20 Unexplained Anomalies in Shallow and 

 Restricted Water Performance. It has been the 

 experience of most analysts and experimenters on 

 ship behavior in confined waters that no sooner 

 have they found a rule which appears to predict 

 performance reasonably well than a case crops 

 up which upsets all their calculations. This 

 indicates definitely one thing: There are certain 

 actions and effects not yet known and taken into 

 account, involving phenomena not now observed. 



The following extract is from page 6 of TMB 

 Report 640, lebruary 1948, by W. H. Norley: 



"There is some indication, from a study of the sinkage 

 curves, that the sinkage may vary with the beam-draft 

 ratio of the ship. It is recommended that a systematic 

 investigation with models in shallow water be made, the 

 only variable being the beam-draft ratio, to obtain further 

 information on sinkage." 



Very slight imevenness in a solid basin floor, 

 such as in the TMB shallow-water basin, com- 

 bined with bed clearances approaching zero, 

 make it almost impossible to obtain accurate 

 shallow-water resistance data with models. Bed 

 irregularities in ship operating areas may have 

 similar effects on full-scale resistance and power. 

 Unknown current magnitudes and directions at 

 the several depths over an irregular bed may also 

 influence ship behavior in an unpredictable man- 

 ner. 



Until it is known what to observe, careful 

 experimenters will record all the data which can 

 conceivably have any bearing whatever on the 

 result, when they conduct ship trials in shallow 

 and restricted waters. 



As an indication of some of the unexplained 

 anomalies which now exist, there are fisted here- 

 under some data given to the author in January 

 1949 by the then Captain Arleigh A. Burke, 

 USN, based upon his experience as commanding 

 Officer of the light cruiser U. S. S. Huntington 

 (CL107): 



(1) When operating in the shallow waters of the 

 River Plate, with depths varying from 26 to 35 

 ft, draft of the ship about 25 ft, it was possible 

 to achieve a ship speed of about 15 kt by making 

 revolutions for about 19 kt in deep water. How- 

 ever, when increasing the rate of propeller rota- 

 tion above this value, it was stated that the ship 

 actually ran more slowly than 15 kt. 



(2) It was found difficult to move the ship 

 sideways in shallow water. This included attempts 

 to move the bow and the stern separately as 

 well as to move the ship bodily in crab fashion, 

 by the motion known as sidling. 



(3) When passing through the Suez Canal the 

 ship would keep herself more or less in the center 

 of the channel without any appreciable steering. 

 If she sheered slowly toward one bank a positive 

 differential pressure would build up on the bank 

 side of the bow and push the bow back toward 

 midchannel. Having swung so that the bow was 

 headed away from the shore the ship would 

 work herself out from the near bank. 



61.21 Summary of Shallow- and Restricted- 

 Water Effects. Summarizino; the effects of 



