Sec. 65.9 



GENERAL PROBLEMS OF DESIGNER 



459 



halve the 30-deg slope of the special models, 

 giving 15 deg, but at the same time it appeared 

 risky to double the ship slopes, involving values 

 as high as 16 to 18 deg. Nevertheless, this pro- 

 cedure narrowed the choice from somewhere in 

 the wide range of 21 deg, between 30 and 9 deg, 

 to the much smaller range of 3 deg, between 18 

 and 15 deg. On the basis that no ship would be 

 built with an arch stern unless a model was first 

 thoroughly tested, the maximum tunnel slope 

 was set at 18 deg. Subsequent flow tests on the 

 model showed no separation or harmful flow of 

 any kind. 



65.8 Adherence to Design Details in Construc- 

 tion. Although all features of ship construction 

 are outside the scope of this book it is considered 

 rather important to point out that, no matter 

 how good the ship design, it requires a thorough 

 and intensive follow-through, from beginning to 

 end of the building period. Only in this way 

 can a designer insure that the continual pressure 

 to cut corners in production does not affect the 

 service performance and reliability of the vessel. 

 In the event of failure or casualty the blame is 

 liable to fall as much on the designer as on the 

 builder. 



Nowhere is this follow-through more necessary 

 and important than in the shaping, assembly, 

 and finishing of the underwater hull surface and 

 appendages. The most carefully calculated and 

 cavitation-free rudder or strut shape is of no 



avail unless the form indicated on the plans is 

 faithfully reproduced on the ship. Indeed, a 

 projecting welding bead, transverse to the flow 

 in a high-velocity region near the surface, can 

 and has produced cavitation, noise, and vibration 

 of plate panels. Not only that, it has produced 

 erosion, first of the paint coating and then of the 

 plate metal itself. 



65.9 Guaranteeing the Performance of a New 

 Ship Design. Finally, the ship designer must, 

 upon the completion of a design, execute what is 

 in effect a guarantee of its performance. Where 

 the apphcation of hydrodynamics is concerned, 

 as in this book, the guarantee relates to propulsion, 

 maneuvering, wavegoing, and all other normal 

 and special operations taken for granted or 

 specifically mentioned in the original require- 

 ments. 



A designer who has, to his own satisfaction, 

 embodied sufficient allowances to meet the various 

 specifications need have little fear that at the 

 conclusion of his work the ship will fail or be 

 found lacking in any element of its behavior. 

 Only too often, unfortunately, the designer's 

 hand is forced in that he is required to make 

 disturbing compromises or to embody features 

 against which he is warned by his better judgment 

 or his engineering instinct. Under these circum- 

 stances he must go to some pains and often to 

 great lengths to assure himself that his estimates 

 and predictions are reliable. 



