Sec. 66.31 



STEPS IN PRELIMINARY DESIGN 



497 



Using the standard formula [PNA, 1939, Vol. 

 II, p. 11, Eq. (22)] and assuming different values 

 for the gyr adius k and the transverse metacentric 

 height GM. 



2irk 



T = 



v: 



gGM 



(1) For a GM of O.OQBj, or 4.38 ft, 



(a) When k = 0.25Bx or 18.25 ft, T = 9.65 

 sec, for a complete roll. This is somewhat too 

 small for the comfort of passengers and the safety 

 of package cargo. 



(b) When k = O.SOBx or 21.9 ft, T = 11.58 sec. 

 This is still rather short for comfort, on a rolling 

 ship, but not too short as to be disturbing at this 



(2) For a GM of 0.045x or 2.92 ft, 



(a) When k = 0.25Bx or 18.25 ft, T = 11.82 sec 



(b) When k = O.SOBx or 21.9 ft, T = 14.19 sec. 



It is apparent that, with the large beam, the 

 lowest permissible GM will produce the most 

 comfortable ship. 



66.31 First Longitudinal Weight and Buoyancy 

 Balance. Before completing this first stage of the 

 preliminary design it is necessary to determine 

 approximately whether, for the designed maxi- 

 mum service-load condition: 



(a) The ship has reasonable longitudinal balance, 

 with the CG in nearly the same transverse plane 

 as the CB 



(b) The volumes of the various parts of the ship, 

 as well as of the passenger quarters and cargo 

 spaces, can be contained within the total volume 

 of the hull and superstructure. This requires a 

 re-check of the hull volume estimate of Sec. 66.8. 



(c) There is sufficient room within the hull 

 structure for certain large items such as reduction 

 gears or motors on the propeller shaft 



(d) The hull volume is so large as to be objection- 

 able from the standpoint of ship handling in a 

 strong wind. 



A body plan on a much larger scale than the 

 small sketches of Fig. 66.0 is now available in 

 Fig. 66. P for an adequate estimate of the areas, 

 volumes, and moments to be used in this opera- 

 tion. Further, it is assumed that the abovewater 

 hull has already been roughed out, as in the upper 

 part of Fig. 66. P, and that a rough outline has 

 been made of the upper works (superstructure). 

 It is now possible to sketch in the principal 

 subdivisions between passenger and crew accom- 

 modations, package-cargo space, liquid-cargo 

 tanks, fuel-oil tanks, and machinery spaces. 

 These are indicated by the hatched areas on the 

 profile of Fig. 66.S. 



A rough integration of these volumes, allowing 

 5 per cent for ship structure in the dry spaces, 

 gives the tentative volumes of Table 66. h. For 

 comparison there are listed also the required 

 volumes of Sec. 66.8. 



It is next necessary to determine whether the 



TABLE 66.h — Second Estimate op Volumes for ABC Design 



