Sec. 60.12 



SHIP-POWERING DATA 



379 



Twin-Screw Mine-Lavjer 

 TMB Model 5594 

 Model Propellers 1975,1976 

 SNAME RD 5heet 98 

 Conditions for This SPTest: 

 H- 17,5 ft W= 6,700t 



Trim, Zero 5=28,510 ft^ 

 Rudder Horn, Shafts, Struts 

 D= IZ.67 ft; P- 13.92 ft;Z = 3 

 Cm/D = 0.252-, to/D = 0.043 

 Propellers Turnino Outward 

 Test 3, 6Jun 1940, ot EMB 



II 12 13 14 15 16 17 18 19 20 21 22 23 

 Ship Speed, \\t 



Fia. 



D.T Self-Peopelled Model Test Curves 

 FOB A Twin-Screw Naval Vessel 



(d) Minelayer U. S. S. Terror (CM5); EMB model 3594 



and EMB model propellers 1975 and 1976. SNAME 

 RD sheet 98. Fig. 60.T reproduces the self-propul- 

 sion data of Test 3, dated 6 Jun 1940. 



(e) Medium-size Atlantic liner America; SNAME, 1940, 



pp. 9-49, esp. Fig. 2 on p. 11. The first portion of 

 this paper was abstracted in SBMEB, Aug 1940, 

 pp. 278-286; the self-propulsion data curves were 

 published on p. 286. The tests were run on EMB 

 model 3525 with EMB model propellers 1803 and 

 1804. 



(f) Medium-size Atlantic liners Constitution and Inde- 



pendence. SNAME RD sheet 158; SNAME PD 

 and SPD sheets not yet numbered (1955). 



(g) Atlantic liner Manhattan, with normal V-type stern 



and bossings, as represented by EMB model 3041. 



A complete set of self-propulsion curves is given in 



Fig. 20 on p. 114 of SNAME, 1947. Table 3 on p. 



113 gives complete general characteristics of this 



vessel, 

 (h) Twin-skeg Manhattan design, TMB model 3898. A 



complete set of self-propulsion curves is given in 



Fig. 21 on p. 114 of SNAME, 1947. Table 3 on p. 



113 gives complete general characteristics for the 



hypothetical vessel represented by this model, 

 (i) Twin-screw tanker of extreme beam, Sun Shipbuilding 



and Dry Dock Company design, TMB model 3817, 



with normal form of stern. Self-propulsion curves 

 are given by Fig. 15 on p. 110 of SNAME, 1947; 

 general characteristics are in Table 1 on p. 109. 



(j) Twin-skeg tanker of extreme beam, adapted from (i) 

 preceding. TMB model 3821, for which complete 

 self-propulsion curves are given in Fig. 16 on p. 110 

 of SNAME, 1947. The general characteristics of the 

 prototype vessel are found in Table 1 on p. 109 of 

 the reference. 



(k) U. S. Maritime Administration 622-ft 23-kt design, 

 TMB model 4424, ETT model 1448-1, for which 

 complete self-propulsion data arc given in SNAME, 

 1955, Fig. 4, p. 730. The body plan and character- 

 istics of this vessel are given on pp. 728-729 of the 

 reference. 



III. Quadruple-Screw Vessels 



(a) Large Atlantic liner S. S. Normandie (later U. S. S. 

 Lafayette); SNAME RD sheet 39; also PD and 

 SPD sheets, not yet numbered (1955). 



The technique of predicting, from the test 

 results on model ships and propellers, the shaft 

 power, the rate of rotation of the propulsive 

 device (s), and other factors in the full-scale ship 

 performance has not yet (1955) been perfected 

 so that scale effects are reliably eliminated. 

 R. B. Couch has published a model-ship com- 

 parison, reproduced here in Table 60. c, in which 

 the ratios of model prediction to ship performance 

 are given for ten different ships [6th ICSTS, 1951, 

 Table IV, pp. 146-147]. The comments which 

 follow are adapted from those of Couch, as 

 published on page 145 of the reference cited: 



(1) The model-ship comparisons of Table 60. c 

 are in general based on the identity of predicted 

 and measured shaft power Ps ■ The model pro- 

 pulsion tests were run at the ship point of self- 

 propulsion with all appendages fitted; in other 

 words, the theoretical added friction on the model 

 was compensated for by helping the model along. 

 The ship-trial data were corrected to zero relative 

 wind. Where thrustmeters were fitted the com- 

 parisons show close agreement on thrust in some 

 instances. Uncorrected open-water propeller data 

 were used throughout. 



(2) A detailed analysis of the values tabulated 

 is not available. It is hoped that such an analysis 

 will shed further light on the scale-effect problem. 

 However, certain trends may readily be noted: 



(i) In all cases the rate of propeller rotation 

 for the model is higher than for the ship 



(ii) In nearly all cases the ship wake fractions 

 are higher than those of the models 



(iii) On the assumption of thrust-deduction 



