CHAPTER 78 



Model-Testing Program for a Large Ship 



78.1 Preliminary 868 



78.2 Model-Test Data Desired for a Major-Ship 



Design 868 



78.3 Model-Test Notes for Preliminary ABC 



Designs 869 



78 . 4 Use of Stock Model Propellers for First Self- 



Propulsion Tests 870 



78 . 5 Displacement and Draft Conditions .... 871 



78.6 Resistance Tests 872 



78.7 Wave Profiles and Lines of Flow 873 



78.8 Flow Observations with Tufts; Sinkage and 



Trim; Wake Vectors 874 



78.9 Self-PropeUed Tests 875 



78.10 Open- Water Propeller Tests 876 



78.11 Neutral Rudder Angle and Maneuvering 



Tests 876 



78.12 Controllability Tests in Shallow Water ... 876 



78.13 Wavegoing Model Tests 877 



78 . 14 Vibratory Forces Induced by the Propeller . 877 



78.15 Reporting and Presenting Model-Test Data . 877 



78.16 Te.st Results for Models of the ABC Ship . . 879 



78.17 Comments on Model Tests and Analysis of 



Data ■ 879 



78 . 18 Proposed Changes in Final Design of ABC 



Ship 896 



78 . 19 Comments on Illustrative Preliminary-De- 

 sign Procedures of Part 4 898 



78.1 Preliminary. Progress of the hydrody- 

 namic design, on paper, is suspended when: 



(a) As many features have been developed, and 

 as much of the behavior has been predicted, as 

 the state of the art permits, working from refer- 

 ence books and data only 



(b) The design has been narrowed to say two 

 alternatives, for which an evaluation on paper 

 indicates no preference 



(c) The design is so novel that predictions of its 

 probable performance can not be made on a 

 basis of existing data or experience. 



This is the stage at which to make towing and 

 self-propelled model tests. Few ships, especially 

 of an untried design, can be built so quickly and 

 cheaply that some time and expense devoted to 

 model testmg is not worth while. Durmg World 

 War II a model test worked into a total prelimi- 

 nary-design period of less than one week made it 

 possible to eliminate one propeller, one shaft, 

 and one propelhng plant from what had originally 

 been a triple-screw layout. For a vessel of the 

 si^e of the ABC ship, and for a design with its 

 unusual features, a series of tests embracing 

 everything within the capacity of the modern 

 model basin estabhshment is considered well 

 justified. It is both good naval architecture and 

 good advance uisurance. Such a program, laid 

 out in this chapter, was actually carried through 

 for the ABC design at the David Taylor Model 

 Basin before this volume was completed, except 



for the tests relating to maneuvering and wave- 

 going. 



Many marine architects are not famihar with 

 the capabilities of an up-to-date ship-model 

 testing plant and do not reahze how much 

 assistance can be rendered in confirming or 

 modifying a ship design. A typical test schedule 

 is therefore described in some detail. 



78.2 Model-Test Data Desired for a Major- 

 Ship Design. The specific model-test data listed 

 here are intended to confirm, or other-wise, the cor- 

 responding data predicted in the course of the 

 preliminary hydrodynamic design, worked up in 

 the preceding chapters of Part 4. These cover, 

 briefly: 



(a) Resistance of the hull, first without append- 

 ages (bare hull), and then mth them 



(b) Sinkage and trim of the hull; this may be 

 measured on the hull either when it is bare or 

 with appendages 



(c) Wave profile and flow pattern around the 

 hull, first without appendages, to determine the 

 traces of the roll-resisting keels and to check 

 other features; later -with appendages and with 

 the propeller (s) working 



(d) Wake vectors or flow directions at positions 

 selected for the arms of struts to support propeller 

 bearings, as a guide to orienting or tmsting these 

 arms into the lines of flow 



(e) Wake vectors at the propeller position (s), 

 with struts, bossings, or other appendages in 

 place ahead of the propeller(s) 



868 



