Sec. 60.^ 



SHIP-POWERING DATA 



359 



wake, some of it listed subsequently in this section, 

 in which only the fore-and-aft or direction-of- 

 motion components of the actual wake velocities 

 are indicated, as described in Sec. 11.4. The 

 preponderance of these data might lead a marine 

 architect to believe that this method of wake 

 representation is adequate. The fore-and-aft 

 actual-velocity components do indeed serve as the 

 basis for the orthodox wake fraction in everyday 

 use for powering estimates and for some analytic 

 work. Nevertheless, it is important to realize 

 that they tell only part of the story so far as flow 

 at the propeller positions is concerned. The 

 reasons for this are set down in Chap. 11 and in 

 Sec. 60.7 following. The 3-diml representation of 

 Fig. ll.F and of Figs. 60.D through 60. J in Sec. 

 60.6 of the present chapter gives a far more 

 adequate, more accurate, and more useful indica- 

 tion of the flow situation in which the propeller 

 must work. 



Additional reasons for making use of a 3-diml 

 wake diagram which shows the true water veloc- 

 ities, in both magnitude and direction, are 

 brought out in Sec. 60.7. 



It is true that the plotting of wake-survey 

 diagrams in terms of contours of longitudinal- 

 velocity components F(l — w) or of wake fraction 

 w reveals certain features not well illustrated by 

 the TMB 3-diml wake-vector diagrams of Figs. 

 ll.F and 60.D through 60.K of Sec. 60.6. For 

 example, the wake-contour diagram for TMB 

 twin-skeg model 3898, published in SNAME, 

 1947, Fig. 32 on page 121, reveals the general 

 pattern of wake irregularity more vividly than 

 the 3-diml survey diagram of Fig. 22 of the 

 reference, from which it was constructed. 



A brief of sources embodying wake-survey 

 diagrams with contour and other plots of local 

 fore-and-aft velocity components or wake frac- 

 tions is given here for the benefit of the reader: 



(a) Calvert, G. A., "On the Measurement of Wake 



Currents," INA, 1893, Vol. XXXIV, pp. 61-67 and 

 Pis. I, II, and III. Figs. 3, 4, and 5 on PL II are 

 early wake-survey diagrams showing true wake 

 speeds, in the lines of flow, as percentages of the 

 ship speed. Calvert endeavored to account for the 

 observed wake velocities by combining the wave 

 wake with the viscous wake but a rather large dis- 

 crepancy remained because he did not take into 

 account the wake due to potential flow. 



(b) Kempf, G., "The Wake of a Ship in Relation to that 



of its Model," SBSR, 14 Feb 1924, pp. 194-196. 

 Describes wake wheels or vane wheels and gives 

 results of model tests. 



(c) Kempf, G., "Neue Betriebserfahrungen und Ent- 



wicklungen der Schiffbau-Versuchstechnik (New 

 E.xperiences and Developments in the Technique 

 of Ship Trials)," WRH, 1 Nov 1930, pp. 437-442, 

 esp. Figs. 5, 5a, 8, and 9. English version in TMB 

 Transl. 3, Dec 1930. 



(d) Weitbreclit, H. M., "Mitstrom und Mitstromschrau- 



ben (Wake and Wake-Adapted Propellers)," WRH, 

 15 Dec 1930, pp. 505-507, esp. Figs. 6, 7, and 8 



(e) Wake-fraction diagrams, indicating the variation in 



this fraction around a propeller tip circle, for 

 sterns with V- and U-sections, are shown on page 

 254 of a paper by Dr.-Ing. E. Foerster entitled 

 "Speed and Power of Ships" [MESA, May 1930]. 

 These indicate a minimum wake fraction of about 

 0.42 for the U-shaped run and of about 0.18 for 

 the V-shaped run. Similar diagrams, showing the 

 variations in wake fractions around a screw- 

 propeller disc behind different forms of bossing, are 

 given at the bottom of pages 256 and 257 of the 

 reference quoted. 



(f) Weitbrecht, H. M., "Uber Mitstrom und Mitstrom- 



schrauben (On Wake and Wake-Adapted Pro- 

 pellers)," STG, 1931, Vol. 32, pp. 117-133; also 

 Figs. 23(a), 23(b), and 23(c) on p. 350, SNAME, 

 1950 



(g) Kempf, G., Mitstrom und Mitstromschrauben (Wake 



and Wake-Adapted Propellers)," STG, 1931, pp. 

 134-152. This paper contains a considerable number 

 of contour diagrams, showing longitudinal com- 

 ponents of velocity and wake fractions, and other 

 features. Fig. 25 on p. 793 of SNAME, 1955, is 

 adapted from one of these diagrams. 



(h) Baker, G. S., "Wake," NECI, 1934-1935, Vol. LI, 

 pp. 303-320 and D137-D146. Shows wake-survey 

 diagrams for a number of models. 



(i) Yamagata, M., "Wake Measurement by a Working 

 Propeller," 3rd ICSTS, Berlin, 1934, p. 67 



(i) Yamagata, M., INA, 1934, pp. 286-396, esp. pp. 

 387-388 and PI. XXXIX. 



(k) Michel, F., "Stromungserregte Resonanzschwing- 

 ungen (Resonant Vibration Caused by Flow)," 

 WRH, 1 Feb 1939, pp. 29-31 



(1) German twin-screw ship Tannenberg. Contours of 

 equal fore-and-aft wake fraction are given by G. 

 Kempf in WRH, 15 Jun 1939, pp. 167-174, especi- 

 ally pp. 170-171. An English version of this paper 

 is found in TMB Transl. 91, Jul 1941, where the 

 wake-survey and analysis diagrams appear on pages 

 10 and 11. 



(m) Twin-skeg Manhattan, contours of equal longitudinal 

 components of wake velocity abaft one skeg and 

 for a considerable distance beyond ; SNAME, 1947, 

 Fig. 32, p. 121 



(n) Troost, L., "The Effect of Shape of Entrance on Ship 

 Propulsion," INA, 1949, pp. 169-170. Contours are 

 given of equal wake fraction (axial component only) 

 over the propeller disc of a small coaster, together 

 with graphs showing the circumferential variation 

 of the wake fraction for various radii. 



(o) Harvald, S. A., "Wake of Merchant Ships," Danish 

 Technical Press Copenhagen, 1950, esp. p. 80 



(p) Normandie, transatlantic passenger liner. Two dia- 

 grams of the wake magnitudes abaft the outboard 



