)12 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 67.7 



Fig. 67.F Comparison of Residuabt-Resistance- 

 Per-Ton Values for Normal and Bulb Bows 



all the bulb sections intersect the baseline. A 

 good shape for the bulb section, extending all 

 the way up to the DWL, and lying in or projected 

 upon the transverse plane of the FP, is that of a 

 decanter. As a starter in laying out this section, 

 first draw two short vertical lines at the DWL, 

 at the half-beams selected for the stem, and then 

 lay off the keel half-siding on each side of the 

 baseline. From the outer edges of the keel draw 

 two short floor hues at a suitable rise-of-floor 



angle. This may, for a ship to run in the open sea, 

 range from 20 to 45 deg, depending upon the 

 contemplated width of the bulb proper. The aim 

 is to prevent objectionable pounding and slam- 

 ming under the bulb. 



If the bulb section were made triangular, with 

 its apex at the DWL and with a zero rise of floor, 

 its width at the bottom would be that of the 

 section area at Sta. divided by half the draft. 

 Two diagonal lines are drawn, one of which is 

 marked DC in Fig. 67. G, diagram 1, representing 

 the two sides of this triangle. With a diameter 

 which is of the order of one-eighth greater than 

 the total bottom width of the triangle, draw a 

 construction circle tangent to the baseline. Using 

 the half-beam at the DWL, the keel half-siding, 

 the floor lines, the straight-sided triangle, and the 

 construction circle as guide lines, sketch in a 

 decanter shape, as is done in diagram 1 of Fig. 

 67.G for the ABC ship. The fs value here is 0.06. 

 It is found that, in general, the bulb section 

 passes close to the upper intersection of the 

 triangle and the construction circle, and that its 

 maximum beam is about that of the circle. 



Adhering strictly to Wigley's criterion (6), 

 quoted earlier in this section, that the submergence 

 of the top of the bulb be not less than its maximum 

 breadth, the construction circle for any bulb 



TABLE 67.a — Derivation of Rr/A Values fob Two TSS Ships Without Bulb Bows 

 The data presented here are taken from the TSS contours of 7?k/A given by D. W. Taylor in S and P, 1943. The 

 derived values of Rr/A are plotted on Fig. 67.F. 



FINE SHIP, Series A 



FAT SHIP, Series B 



3 35-2 25 



Multiplier = Mi = — =0.733 



^ 3.75-2.25 



3 20-2 25 



Multiplier = Mi = — = 0.633 



3.75-2.25 



