498 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 66.32 



13 12 

 Cofferdom Spaces not shown 



"9 S 7 6 5 



Inner Bottom Spaces not complete 



Fig. 66. S Tentative Distribution op Principal Volu.mes in the ABC Design 



ship trims properly with the principal weights in 

 the locations indicated. Selecting approximate 

 centers of gravity for each of the items the 

 longitudinal weight balance comes out as indi- 

 cated at the bottom of Table 66.i. 



This tentative balance for the designed-load 

 condition is necessarily crude. The volume and 

 location of the package-cargo spaces, the tankage, 

 the machinery spaces, and other items on Fig. 

 66.S are still only approximate. Since these 

 matters involve static problems only, not directly 

 related to the hydrodynamic design, they are 

 followed only to the point of checking the trim 

 in two of the variable-weight conditions, de- 

 scribed in Sec. 66.32. 



However, an important hydrodynamic-design 

 rule, for these as well as for the later stages 

 described in Chap. 67, is well kept in mind: If, 



after developing what is considered to be an 

 easily driven hull shape, the CG is found to be 

 offset from the CB of that shape, do not change 

 the shape to bring the CB to the CG position. 

 Rather, rearrange the internal spaces, volumes, 

 and weights to bring the CG to the CB position 

 of the low-resistance hull. 



66.32 Propeller Submersion and Trim in 

 Variable-Load Conditions. Havi ng fou nd reason- 

 able agreement in the LCG and LCB values for 

 the weight balance in the designed-load condition, 

 at the 26-ft draft in salt water, there remains to 

 consider the situation when: 



(1) The vessel is only partly loaded, as when 

 leaving Port Amalo in the hurricane season, 

 condition Hi of Table 66.f of Sec. 66.16 



(2) When arriving at the river mouth below Port 



TABLE 66.1 — First Longitudinal Weight Balance 

 Moment arms are in terms of station spacing, 25.5 ft. Moments are taken about the midlength at the DWL, Sta. 10. 



-2,415 

 16,400 



= 0.1473 station-length abaft Sta. 10 



The tentative CG position is at Sta. 1 . 1473 so that LCG is . 5074 L. Since the tentative LCB is . 506 L, it should not 

 ■ be difficult to bring the CG forward by 0.0014 L or about 0.71 ft. 



