Sec. 56.6 



OBSERVED SHIP-RESTSTANCE DATA 



303 



and other members of the TMB staff, are given 

 in a form which employs a completely 0-diml 

 presentation [Gertler, M., "A Reanalysis of the 

 Original Test Data for the Taylor Standard 

 Series," TMB Rep. 806, Mar 1954, Govt. Print. 

 Off., Washington]. The faired resistance data are 

 given as curves of specific residuary-resistance 

 coefficient Cr on a basis of both Taylor quotient 

 T, = F/VL and Froude number /^„ = F/V^. 

 Two of the major proportions used are, as before, 

 the B/H ratio and the (longitudinal) prismatic 

 coefficient Cp . The scope of the series has been 

 enlarged to include a third B/H ratio of 3.00 in 

 addition to the ratios of 2.25 and 3.75 published 

 in the 1910, 1933, and 1943 editions of D. W. 

 Taylor's "The Speed and Power of Ships." The 

 intermediate values were obtained by interpola- 

 tion, using the reworked data for the hitherto 

 unpublished EMB Series 20 which had a B/H 

 ratio of 2.92. 



Instead of Taylor's dimensional displacement- 

 length quotient the Gertler reworking makes use 

 of the 0-diml volumetric coefficient Cv = F/L3 , 

 expressed as a simple number times 10~^. This 

 number, without the 10"^ factor, is exactly the 

 same as the ATTC fatness ratio F/(0.10L)'. The 

 origir ial T aylor wetted-surface coefficient Cws = 

 S/'VAL, which is di mens ional, is replaced by 

 the 0-diml Cs = S/VVL. 



These and the remaining steps in the reworking 

 process are explained most comprehensively and 

 meticulously by Gertler in the Preface and intro- 

 ductory portions of TMB Report 806, previously 

 referenced. 



The new presentation differs markedly from the 

 original. Examining a pair of facing pages, repro- 

 duced as the two parts of Fig. 56. D, one sees the 

 graphs of C^ for various volumetric coefficients 

 Cv = V/L\ or fatness ratios F/(0.10L)', extend- 

 ing from the lowest speed-length quotient T, of 

 0.5 to the highest value of 2.0. All the humps and 

 hollows in the complete range of Cr , for any 

 volumetric coefficient, are visible at a glance. 



The pair of facing pages embodied in Fig. 56.D 

 is used with another pair of pages, not reproduced 

 here, to derive a preliminary estimate of the 

 residuary resistance of the ABC ship, by the 

 method described in Sec. 57.6 and illustrated in 

 Table 57.c. The characteristic spot for the ABC 

 ship values listed in that table is added to the 

 figure. 



Gertler's data have the disadvantage that the 

 effect of variation of Cp on Rr/A is not readily 



apparent. By moving right and left across the 

 page, the original Taylor contours show clearly 

 the change in Rr/A for a change in Cp . However, 

 in the range of T, or F„ where friction resistance 

 predominates, say below a T^ of 1.15, F^ of 0.342, 

 the selection of Cp is not made on the basis of a 

 minimum value of Rr/A. The effect of 

 A/(0.010L)' or F/(0.10L)' on residuary resist- 

 ance is shown well by both the Gertler reworking 

 and the original Taylor Standard Series contours. 

 The Gertler data have the advantage that, with 

 three B/H ratios, interpolation is easier and more 

 accurate. Indeed, for many B/H values close to 

 2.25, 3.00, and 3.75, and for a preliminary resist- 

 ance estimate, interpolation for beam-draft ratio 

 may be omitted entirely. 



Although never stated in print in so many 

 words it was felt by many that the Rr/A con- 

 tours of the 1910, 1933, and 1943 editions of "The 

 Speed and Power of Ships" were rather "heavily" 

 faired, probably because in some regions there 

 were not many spots with which to establish the 

 proper contour positions on the diagrams. Com- 

 parisons of Pe for random models with the Pb 

 values of the TSS models of the same proportions, 

 corresponding to the EHP/Taylor EHP ratios of 

 the SNAME Expanded Resistance Data sheets, 

 when plotted on F or T^ , produced what are 

 known as "angleworm" curves. Although many of 

 these random models represented ships of superior 

 and outstanding performance, their "angleworm" 

 curves showed rapid and often violent plus and 

 minus fluctuations in the values of [1 — EHP/ 

 Taylor EHP], on a basis of variation in the speed- 

 length quotient T^ . 



When the TSS data were reworked in 1948- 

 1951, all "heavy" fairing was carefully avoided. 

 Nevertheless, variations in the ratio of P^ to the 

 reworked TSS Pe values still occur. If not angle- 

 worm in shape they are sinuous and irregular, 

 and they are not always consistent with the varia- 

 tions of the original data. Additional comments 

 on this feature are found in Sec. 57.6. 



56.6 Resistance Data for Very Fat Ships. The 

 lack of resistance data for ship forms of large 

 0-diml fatness ratio F/(0.10L)', for which the 

 Takagi Series described in Sec. 56.4 fills a partial 

 need, led to the analysis of EMB and TMB test 

 data for 44 fat models by R. F. P. Desel and J. T. 

 Collins. The results are embodied in an MIT 

 thesis submitted by them, dated 1952 [copy in 

 the TMB Ubrary]. Although there were 13 tug 

 models in the group, and 15 combinations of the 



