Sec. 61.19 



PRF.niCTEn BEHAVIOR IN CONFINED WATERS 



413 



All Dimensions on this 

 N Diatjram Are in Meters 



Yowinq Moment N 

 Acting to 5wi no 

 Bow Away From 

 Near Bonk 



\ Loterol Force 

 NActinq Away From' 

 Near Bonk 



Offset From 



Centerline of 

 Conal 



Centerlina of Conol 



Width of Prism at Bottpml 



it BottomI I ^ rv 



1^ ^' ^1 oee Dioqram 3 



r p^ ** of Fiq.ei.N 



of WQter| Surface. 



Fig. 61.0 Diagram op R. Brard's Full-Scale 

 Prototype of Model 111 in Full-Scale Suez- 

 Canal Section 



Supercritical Speeds. If supercritical speeds are 

 reached, as they can be on many fine, fast vessels 

 in shallow-water areas where there are no limita- 

 tions on squat, on the eroding action of waves 

 along the banks, and on interferences with other 

 craft, the shaft power at certain speed-length 

 quotients may fall below the value required in 

 deep, unUmited water. In Sec. 29.7 of Volume I 

 it is explained that a following vessel riding on 

 the front of a transverse wave created by a 

 leading vessel is able to keep station at reduced 

 shaft power and with a reduced rate of rotation 

 of its propulsion device(s). In actual cases, 

 following destroyers have been able to hold 

 position with a 20 per cent reduction in rpm. 



Data relating to the resistance, speed, and 

 change of trim of a heavy cruiser model running 

 at a supercritical speed in a model channel are 

 given by E. A. Wright [SNAME, 1946, Fig. 29, 



p. 396]. Similar data are to be found in some of 

 the references of Sec. 61.22. 



61.18 Data on Offset Running Positions and 

 Steering in a Channel. Few published quantita- 

 tive data are available on the offset running of a 

 ship between canal walls, or alongside a single 

 wall, as depicted in Figs. 18. G and 18. H and 

 described in the accompanying text of Sees. 18.5 

 and 18.6 of Volume I; see also Fig. 61.0. The 

 two outstanding sources appear to be: 



(1) Garthune, R. S., Rosenberg, B., Cafiero, D., and 



Olson, C. R., "The Performance of Model Ships in 

 Restricted Channels in Relation to the Design of a 

 Ship Canal," TMB Report 601, August 1948. 

 Section 4 of this report covers the behavior of models 

 in central and offset positions, in varied depths of 

 channel, both towed and self-propelled, and with 

 different rudder angles. During many of these tests 

 the ship model was stationary in a current of moving 

 water. Yawing moments, lateral forces, and rudder 

 angles to maintain equilibrium conditions are 

 given in terms of the other variables. 



(2) Brard, R., "Maneuvering of Ships," SNAME, 1951, 



pp. 229-257. This paper reports the results of tests 

 on three ship models in a model channel represent- 

 ing the Suez Canal [SNAME, 1951, pp. 232-242]. 

 Graphs of lift, drag, and yawing moment coefficient, 

 Cy , Ci , and C , respectively, are supplemented in 

 Figs. 10 and 11 of the reference by graphs of lateral 

 forces and turning moments for a rather wide range 

 of yaw angles in three different lateral positions, 

 first on the canal centerline and then offset by 0.15 

 and 0.30 of the 42-meter bottom width of the full- 

 scale canal section. The ship beam was 25.9 meters 

 or 25.9/42 = 0.617 of that width, and its draft was 

 10.4/13 or 0.8 of the canal depth. 



From Brard's Fig. 10 on page 241 of the refer- 

 ence the lateral force on the ship represented by 

 Paris model 111 was, at the maximum offset, 

 found to be zero at about 1.2 deg yaw angle away 

 from the near bank. From Brard's Fig. 11 on 

 page 242 the value of the turning-moment 

 coefBcient C„ at this yaw angle was about 0.075, 

 acting to swing the bow away from the near 

 bank. A rudder angle apphed toward the bank, 

 to counteract this yawing moment away from it, 

 would set up a lateral force to push the ship 

 away from the bank. Equilibrium would therefore 

 be achieved at a yaw angle less than 1.2 deg. 



This is the reason why, to get the ship away 

 from the near bank and back into the center of 

 the channel, rudder angle is appUed toward the 

 near bank! 



61.19 Prediction of Ship Resistance in Canal 

 Locks. The force required to push or pull a 

 close-fitting ship into or out of a lock, discussed 



