316 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 57.5 



factor. For example, it has to be decided whether 

 the shape contemplated for the design will have 

 less (or more) resistance than the standard-series 

 or reference hull of the same proportions. This is 

 afforded, after a fashion, by the EHP/Taylor 

 EHP or "angleworm-curve" ratios of the SNAME 

 ERD sheets. However, with many such ratios 

 at hand, it is still difficult to formulate anything 

 approaching systematic rules for guidance in 

 this matter. A bulb bow carried by the new 

 design, if appropriate, will reduce its resistance 

 below the Taylor Standard Series value. This is 

 one reason why the resistance of the ABC tran- 

 som-stern design, determined by model test, is 

 less than the values calculated earlier in this 

 section. 



Most books on naval architecture give several 

 formulas and methods for predicting the total 

 resistance and effective power of ships in the 

 design stage, perhaps before the lines are drawn 

 and certainly before models are built and tested. 

 For example, G. E. Pavlenko describes no less 

 than eleven methods, dating from 1899 to the 

 present, . including Taylor's Standard Series, 

 Ayre's method, and Doyere's method, for finding 

 the resistance and effective power of merchant 

 and. naval vessels of different kinds ["Soprotiv- 

 leniye Vody Dvizheniyu Sudov (The Resistance 

 of Water to the Movement of Ships)," Moscow, 

 1953, pp. 305-379]. 



In all these cases, however, it is most important 

 to note the limitations on each formula, graph, 

 table, or method, as given in the text. If no 

 limitations are mentioned, they should be sought 

 in other references or directly from those who 

 prepared and published them. 



57.5 Ship Friction Resistance Calculation from 

 Chapter 45. The methods used and the numbers 

 required for a calculation of the ship friction 

 resistance, including all types of roughness, are 

 set forth in detail in Sees. 45.12 through 45.20. 

 The method for calculating the wetted length 

 and thje wetted area S for planing hulls is dis- 

 cussed in Sees. 45.24 and 53.6. 



The method of calculating the friction drag of 

 a submerged submarine is essentially the same 

 as for a surface ship, except for the inclusion of 

 the entire outer area, surrounding what is de- 

 scribed elsewhere as the bulk volume. The trans- 

 verse curvature of the lower part of the hull of a 

 submarine is, as a rule, relatively less than for the 

 bilge corners on a large surface ship with flat or 

 nearly flat floors. However, a submersible hull 



may have rather wide flat surfaces on top, to 

 provide walking space on the superstructure 

 deck. The transverse curvature along portions of 

 the deck edges, even though they are rounded, is 

 likely to be more severe than along the bilge 

 corners of a surface vessel. 



57.6 Residuary Resistance Prediction from 

 Reference and Standard-Series Data. It is pos- 

 sible to approximate the residuary resistance of 

 a surface ship, at a given speed V, or at a series 

 of speeds, by assuming that it is the same as the 

 residuary resistance Ra of a model having the 

 same proportions. Data of this kind can be found 

 in the SNAME RD sheets and similar sources. 

 Continuing the discussion of Sec. 57.4, it is 

 somewhat risky to rely on the proportions Cp , 

 B/H, and A/(0.010L)' (or ^/(O.IOL)') as com- 

 prising the sole as well as the preponderant 

 influences on residuary resistance, neglecting the 

 shape factors entirely. What appear to be minor 

 differences in shape or proportions often produce 

 appreciable changes in resistance. These will not 

 be explained, and can not be allowed for, until 

 our present (1955) knowledge of ship hydrody- 

 namics is considerably extended. 



The calculation of values of Rr/A for a range 

 of speeds and a given set of proportions, by 

 assuming that these are the same as for a TSS 

 "phantom" ship of exactly those proportions, 

 takes it for granted that the shape of the proposed 

 ship is as good as (and no better than) that of the 

 TSS ship. This does not prevent a designer, 

 however, from estimating that his proposed hull 

 will have x per cent less or y per cent more 

 residuary resistance than the TSS "phantom" 

 hull. The difficulty here, as mentioned previously, 

 is the lack of systematic and reliable data for 

 selecting the x- and y-values. 



The contours of Rr/A for the Taylor Standard 

 Series are described in Sec. 56.3. Two sets of them, 

 for V/Vl = 0.90, are illustrated in Figs. 56.A 

 and 56. B. These contours are intended to be used 

 for ships having the same proportions Cp , B/H 

 and displacement-length quotient A/(0.010L)^. 

 The designer may apply, as x- and y-values, 

 increments or decrements of Rr/A. 



An illustrative example of the Taylor Rr/A. 

 method, for the fifth approximation of character- 

 istics in the preliminary design of the transom- 

 stern ABC ship described in Part 4, is given in 

 Table 57. b. The basic data for this stage of the 

 design are listed in the right-hand column of 

 Table 66. e in Sec. 66.11. The proportions required 



