Sec. 67.1 



UNDERWATER-HULL DESIGN 



507 



Fig. 67.C Non-Dimensional Curvature Plots op Designed Waterlines for Three Ships 



that part of the ship which is most vulnerable to 

 damage when taking the ground. Also, as described 

 in Sec. 25.5, a small amount of friction and 

 pressure resistance often may be saved by trim- 

 ming up the forefoot slightly, in addition to 

 saving some wetted surface. 



There may be merit in shifting progressively 

 aft the forward waterline beginnings with depth 

 below the surface, as explained in Sec. 4.8 and 

 illustrated in Fig. 4.1. This is especially true if the 

 waterline entrances are blunt. This bow shape, 

 embodying a heavily raked underwater profile 

 resembling the Maier bow, saves some wetted 

 surface and may result in a slight reduction of 

 pressure drag. There is reason to believe, however, 

 that better performance is achieved, at least at 

 some T, values, by fining all the waterlines and 

 carrying them nearly to the FP. 



The bow profile of the ABC design is the result 

 of combining a bulb bow of slightly ram form, 

 extending forward of the FP, with a sharp cut- 

 water. The former is described in Sec. 67.6 and 



illustrated in Fig. 67.E. The latter is described in 

 Sec. 73.3 and illustrated in Fig. 73.B. 



The stern profile below water is influenced 

 largely by the number and type of stern propul- 

 sion devices selected and their tentative positions, 

 especially if there is a single propdev on or near 

 the centerplane. For a screw propeller, the com- 

 bination of proper hydrodynamic position with 

 the type, shape, and position of the steering 

 rudder(s) leaves little of the stern profile to be 

 delineated to suit the engineering sense of the 

 individual designer. Furthermore, that portion of 

 the stern profile just below the DWL must be 

 considered in conjunction with a larger portion 

 lying above the DWL. In fact, the stern profile is 

 usually so dependent upon other considerations 

 having to do with skeg endings, propeller clear- 

 ances and apertures, transom forms, and similar 

 features that it seems wise to discuss these 

 features in detail in those parts of the book 

 devoted particularly to them. The ABC design 

 is no exception in this respect. 



