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HYDRODYNAMICS IN SHIP DESIGN 



Sec. 63.5 



He needs, furthermore, courage and confidence 

 to strike out boldly for the principal goal by the 

 shortest and most direct route, using first prin- 

 ciples he has learned and adhering almost re- 

 ligiously to fundamentals. It was this procedure 

 which produced the remarkably successful group 

 of large landing craft in World War II, with 

 httle or no experience to fall back upon and the 

 fate of nations at stake. 



63.5 Design as a Compromise. A designer 

 must, at least in the early stages, forget about 

 compromises in a really new and pioneering 

 project. In the first place, he is by no means 

 certain that compromises must be made. He 

 may be surprised to find that a certain stern 

 shape, odd but seemingly necessary, makes him 

 a gift of improved maneuvering and increased 

 deck space as well as more efficient propulsion. 



If compromises must later be admitted, it is a 

 comfort to remember that much of ship design 

 and construction is a compromise. This applies 

 equally to roughing out a dugout canoe from the 

 best available tree, or keeping the propeller tips 

 of a twin-screw ship inside the projected deck 

 fine at the stern. However, if the effects of all 

 the possible variables are known, the designer 

 can choose with wisdom the final size, shape, or 

 form of each of his elements when he makes his 

 compromise. In this way he attains the maximum 

 benefits from the selected combination of all of 

 them. 



Let the compromises be made \vith profes- 

 fessional honesty, sound logic, and good judgment. 

 Let them be known to all and admitted by 

 all. Let them be based upon sturdy reasoning, 

 and let them be tempered by a knowledge and 

 an experienced consideration of all the causes, 

 effects, and consequences. 



63.6 The Essence of Design. British naval 

 architects have an old saying, with respect to the 

 shape and form of a ship, that what looks right is 

 right. This invariably brings an immediate 

 rejoinder about who is doing the looking; mani- 

 festly not just anybody, but one with an experi- 

 enced and practical eye. The eye that has de- 

 liberately been trained becomes accustomed to 

 look not only for efficiency and utility but for 

 beauty, symmetry, and harmony as really 

 essential features of design. It looks, above all, for 

 simphcity and for the feeling of effortless ease 

 that nature puts into many of her most dynamic 

 moods and manifestations. 



A good ship, like a good person, is not neces- 



sarily the largest, strongest, or fastest that can 

 be fashioned, regardless of the other features, but 

 the one in which the best combination of elements 

 produces the most useful, harmonious, and 

 satisfying whole. 



63.7 The Design Schedule for a Ship. This 

 book treats only of the hydrodynamic aspects of 

 ship design, and carries some of these aspects 

 only through the preliminary-design stage. It is 

 difficult, therefore, to visualize the immense 

 amount of thought and planning that has to be 

 put into the design of a ship to achieve the best 

 possible results. According to Ambrose Hunter 

 ". . . it can be truthfully said that it takes every 

 bit as long to design a successful modern trawler 

 as to build one ..." ["The Art of Trawler Plan- 

 ning," Ship and Boat Builder and Naval Architect, 

 London, Feb 1953, p. 259]. What is true for a 

 trawler is true for any vessel, large or small. 



63.8 The Field for Future Improvements in 

 Design. It is natural for the naval architect and 

 marine engineer who is blessed with enterprise 

 and ingenuity to strive for improvements in his 

 work. It is human for him to wish to excel and 

 to surpass the work of others. Remembering that 

 nothing was ever done so well that it could not 

 be done better, he continually entertains the hope 

 that by his improved understanding of basic 

 phenomena he can look forward, as his creations 

 take form and life, to greater efficiency and higher 

 performance. As certain machines appear to be 

 reaching their peak efficiencies and certain 

 engineers or scientists are loudly proclaiming 

 that nothing in the way of radical advances can 

 be hoped for, other engineers and scientists are 

 opening up new Unes of attack which often extend 

 the practicable limits by leaps and bounds. 

 This was the case with the piston-type engine and 

 the screw propeller for airplanes when the jet- 

 type engine appeared upon the scene. It is often 

 said that the screw propeller for ship propulsion 

 is about to reach its limit of performance, where- 

 upon propellers of increased capacity and im- 

 proved efficiency under certain working conditions 

 appear in successful service. 



It is well in ship design as in any other work 

 not to be bound by preconceived ideas of what is 

 possible or by the accomplishments of one's self 

 and others in the past. A designer who is prepared, 

 or in fact is eager to offer novel and improved 

 solutions to old or new design problems, based 

 upon comprehensive knowledge of fundamental 

 physical laws and the confidence bred of successful 



