Sec. 67.6 



UNDERWATER HULL DESIGN 



509 



referenced paper, with additions in pai'entheses 

 by the present author: 



". . . displacement gained in the larger bulbs was removed 

 from the parent form in the region of the design(ed) 

 waterline so as to progressively fine the angle of entrance 

 as bulb size increased. Some displacement also was trans- 

 ferred from the shoulder near the turn of the bilge into 

 the larger bulbs while at the same time the design(ed) 

 waterline was filled out almost imperceptibly at the 

 (forward) shoulder to recover transverse waterplane 

 inertia which had been lost b5f fining the angle of entrance. 

 This latter step, while perhaps not best from pure resist- 

 ance point of view, was nevertheless essential in main- 

 taining stability characteristics constant for the design 

 throughout the range of bulb sizes." 



When considering a bulb bow for a new design 

 it is first necessary to determine whether the 

 speed range is appropriate to its use. D. W. Tay- 

 lor's analysis [S and P, 1943, p. 69] indicates a 

 low Umit of the order of T, = 0.7, F„ = 0.208, 

 but at this low speed the optimum terminal 

 value Ie is close to zero, which is almost out of 

 the question for a ship section-area curve. E. M. 

 Bragg's tests and analysis, in the same reference, 

 indicate a low limit of the order of T, = 0.80, 

 F„ = 0.238. The bulb appears to be most useful 

 in the vicinity of T, = LO. 



An attempt to reconcile the model-te.st data 

 of E. F. Eggert, E. M. Bragg, and A. F. Lind- 

 blad, and to evolve systematic values of the design 

 parameters f e and Ie from them, has so far proved 

 unsuccessful. The design values actually used on 

 a considerable number of vessels whose perform- 

 ance bettered or equaled that of the Taylor 

 Standard Series have been plotted therefore on a 

 basis of speed-length quotient. From these plots 

 the tentative design lanes of Fig. 67. D were 

 derived. They indicate, for T, , a low limit of 

 0.70, F, = 0.208, and a high limit of L50, F„ = 

 0.447. 



Those who use them as interim guides until 

 better rules are developed should recognize the 

 following shortcomings: 



(a) The fs values do not increase indefinitely 

 with T„ beyond the range of T, = 1.5 shown in 

 the diagram. They almost certainly diminish to 

 zero at some upper limit of T, around 1.9 or 2.0. 



(b) The proper value of /g appears to depend 

 upon Cp and the displacement-length quotient 

 A/(0.010L)' or the fatness ratio ^/(O.IOL)', but 

 the various model-test data show conflicting 

 trends. It is probable that the best value of /^ 

 increases with both Cp and the fatness ratio. 



To>^lor Quotient Tq 



0.I6E- 



0.14 E- 

 S 0.12 1- 



< i- 

 g oioi- 



o.y ' die '1 0.^0 r oM ' (Jk 'lab I' o.^^ ' i.ko ' I o.iz I' o.^^ ' ci.^, 



Froude Number f„- V/VqL 



0.15 



-iO.I4 

 ;J0I2 

 "1 0.10 

 -|0.08 

 -=0.06 



Optimum and Minimurn fg Values for o Ronqe of Speed-Length Quotient_^ 



To Give Minimum Pressure Resistance 



•^ 



of f£ Volues. 



^ 0.081- 



.g I" 



S 0.06^ 



0.04 



Lower f?Qnqe of f^ for Existing 



Vessels (1955) 



with Orthodox Bower-Anchor Instoliatio 



' I I I I I I I I I I I I I I I I I I I I I I I I I I 



I I I I I I I I I I I I I 



TQ\jlor Quotient To 

 Fig. 67. D Design Data for Bulb Bows 



