CHAPTER 67 



Detail Design of the Underwater Hull 



67.1 General 504 



67.2 Shape of Vessel Near Designed Waterplane. 504 67.20 



67.3 Waterline Curvature Plots 506 



67.4 Underwater Hull Profile 506 67.21 



67.5 Stem Shape at Various Waterlines .... 508 67.22 



67.6 Design of a Bulb Bow 508 



67.7 Laying Out the Bulb for the ABC Ship ... 510 67.23 



67.8 Check on Bulb Cavitation 514 



67.9 Selection of Section Shapes in Entrance and 



Run 515 67.24 



67.10 Variation of Section Coefficient Along the 



Length 517 67.25 



67.11 Hull Shape Along the Bilge Diagonal ... 517 67.26 



67.12 Side Blisters or Bulges 517 67.27 



67.13 General Arrangement of Single-Screw Stern . 518 67.28 



67. 14 Stern Forms for Twin- and Quadruple-Screw 67.29 



Vessels 520 



67.15 Notes on Three- and Five-Screw Installations 521 67.30 



67.16 The Arch Type of Single-Screw Stern ... 521 



67.17 Flow Analysis for the Arch Type of Stern . . 525 67.31 

 67 . 18 Design of Hull and Appendage Combinations 526 



67.19 Comments on Design of an Unsymmetrioal 



Single-Screw Stern 528 



Proportions and Characteristics of an Im- 



mersed-Transom Stern 529 



The Design of a Multiple-Skeg Stern .... 531 

 Design Notes for the Contra-Guide Skeg 



Ending 532 



Shaping the Hull Adjacent to Propulsion- 

 Device Positions; Hull, Skeg, and Bossing 



Endings 536 



Aperture and Tip Clearances for Propulsion 



Devices 537 



Baseplane and Propeller-Disc Clearances . . 540 

 Adequate Propeller-Tip Submergence . . . 541 

 Design for Minimum Thrust Deduction . . 541 



The Final Section-Area Curve 542 



Modification of Normal Design Procedure for 



a Hull with Keel Drag 543 



Underwater Exhaust for Propelling Machin- 

 ery 545 



General Notes on Water Flow as Applied to 

 Hull Design 545 



67.1 General. Based upon the preliminary 

 ship layout described in Chap. 66, the hydro- 

 dynamic design proceeds with the fashioning of 

 the individual parts, making decisions as to 

 certain secondary form characteristics, such as 

 the more definite determination of the waterlines, 

 section lines, and diagonals, and the shaping of 

 the hull ahead of and adjacent to the positions 

 of the propulsion devices. 



The factors considered here are those which 

 govern smooth-water performance. Whether they 

 may be expected also to result in good behavior 

 during maneuvering and wavegoing, and possibly 

 also during operations in shallow and restricted 

 waters, is considered in Parts 5 and 6 of Volume 

 III and in Chap. 72, respectively, together with 

 particular features which have to do primarily 

 with those special operations. 



The matter of smoothness of the hull and 

 minor fairings is covered in Chap. 75; only the 

 major features are discussed here. 



In this attack on the design problem the size 

 and shape of each part is selected on the basis of 

 its anticipated action in one or more of the 

 fundamental types of flow around it. The whole 

 design is then modified or adjusted on the basis 



of the interactions which may be expected, em- 

 ploying the best available thought and knowledge 

 on the subject. 



67.2 Shape of Vessel Near Designed Water- 

 plane. The principal features governing the 

 shape of the designed waterline for a given 

 speed-length quotient T, or F„ are discussed in 

 Sec. 66.15, together with a presentation of 

 empirical methods for making a selection of good 

 DWL parameters. 



Some consideration is required of possible 

 modifications to the nominal at-rest designed- 

 waterplane shape due to the ship's own waves. 

 If the changes in surface level due to wavemaking 

 at the selected T, are appreciable, and if the 

 sections near the waterplane have sloping sides, 

 the shape of the waterplane ai the actual wave 

 profile may change enough to alter the expected 

 performance. For example, a rather full canoe 

 or whaleboat stern, well tapered in way of the 

 at-rest waterplane but flaring to a wide deck 

 above, may possess a considerably greater slope 

 than the designer intended along the raised 

 surface of the stern-wave crest, with consequent 

 undesirable separation. A heavy flare above the 

 entrance waterline, by humping up the bow-wave 



504 



