CHAPTER 66 



Steps in the Preliminary Design 



66.1 

 66.2 

 66.3 

 66.4 

 66.5 



66.6 

 66.7 



66.8 

 66.9 

 66.10 

 66.11 



66^12 

 66.13 

 66.14 



66.15 

 66.16 

 66.17 



66.18 

 66.19 

 66.20 



General Considerations 460 66.21 



Analj'sis of the Hydrodynamic Requirements 460 66 . 22 



Probable Variable- Weight Conditions . . ■ . 463 



First Weight Estimate 463 66.23 



First Approximation to Principal Dimen- 

 sions; The Waterline Length and Fatness 66.24 



Ratio 464 66.25 



The Longitudinal Prismatic Coefficient . . 467 66 . 26 

 The Maximum-Section Coefficient; The 66.27 



Draft and Beam 468 66.28 



First Estimate of Hull Volume ...... 471 



First Approximation to Shaft Power ... 471 66.29 



Second Estimate of Principal Weights . . . 474 



Second Approximation to Principal Dimen- 66.30 



sions and Proportions 475 



Selection of Hull Shape 476 66.31 



Layout of Maximum-Section Contour . . . 476 



First Estimate Relating to Metacentric 66.32 



Stability 478 



First Sketch of Designed Waterline Shape . 479 66.33 



Estimated Draft Variations 481 



Sketching the Section- Area Curve; The 66.34 



Maximum-Area Position 482 



Parallel Middlebody 483 66.35 



Bulb-Bow Parameters . 485 66.36 



Transom-Stern Parameters . 485 



The Preliminary Section- Area Curve . . . 485 

 Longitudinal Position of the Center of 



Buoyancy 486 



Preparation of Small-Scale Profiles and 



Sections 486 



Molding a New Underwater Form 488 



Bow and Stern Profiles 491 



Analysis of the Wetted Surface 493 



Second Approximation to Shaft Power . . . 493 

 Sketching of Wave Profile and Probable 



Flowlines 494 



Comparison with a Ship Form of Good Per- 

 formance 496 



Abovewater Hull Proportions for Strength 



and Wavegoing 496 



First Longitudinal Weight and Buoyancy 



Balance 497 



Propeller Submersion and Trim in Variable- 

 Load Conditions 498 



First Appro.ximation of Steering, Maneuver- 

 ing, and Shallow- Water Behavior .... 501 

 Preparation of Alternative Preliminary De- 

 signs 501 



Laying Out Other Types of Hulls 602 



Effect of Unrelated Factors Upon the Hydro- 

 dynamic Design 502 



66.1 General Considerations. There are as 

 many ways of executing the hydrodynamic design 

 of a ship, at least in its prehminary stages, as 

 there are ship designers. Each of them is partic- 

 ularly suited to the knowledge, experience, 

 background, and ability of the designer so that 

 each has its particular merits. An example of such 

 an alternative method is given by E. E. Bustard 

 in his paper "Preliminary Calculations in Ship 

 Design" [NECI, 1940-1941, Vol. LVII, pp. 

 179-206 and D49-D62]. A presentation such as 

 that set down here is of necessity limited to a 

 single method, or at most, to two such methods. 

 These are based logically upon a consideration of 

 flow phenomena, paralleling that followed in 

 Parts 1 and 2 of the book. Since knowledge of the 

 hydrodynamic phenomena pertaining to inter- 

 actions between all portions of the ship is not 

 yet complete, part of the preliminary-design 

 work must be accomplished by empirical methods 

 based upon ship-model tests, ship-trial data, and 

 past experience. 



As a means of illustrating the procedures and 

 steps involved in the application of hydrodynamic 

 principles and knowledge to ship design, the 

 preliminary layout and a portion of the final 

 design of the ABC vessel, whose requirements 

 and specifications were formulated in Chap. 64, 

 is carried through in this and succeeding chapters. 

 This craft is of the merchant type and is largely 

 orthodox in character, with elements similar to 

 those found on many past and current designs 

 of ships. A number of unusual features are 

 included, partly to give character to the design 

 and partly to permit application of much of the 

 hydrodynamic knowledge and many of the pro- 

 cedures previously set down. 



66.2 Analysis of the Hydrodynamic Require- 

 ments. Before beguuiing the preliminary design 

 it is well to analyze some of the specifications 

 and requirements formulated in Sec. 64.3. 

 Portions of them require conversion into terms 

 directly applicable to the hydrodynamic design, 

 resulting in quantities which can be used as 



460 



