Sec. 78.15 



MODEL-TESTING PROGRAM FOR A SHIP 



877 



vations are to be made of the successive ship 

 position, torque, thrust if practicable, rate of 

 rotation, and other pertinent data. 



(2) Be left to itself, when running ahead at a 

 speed corresponding to 20.5 kt, with neutral 

 rudder angle and no perceptible swing, to deter- 

 mine whether or not the model deviates progres- 

 sively from its course, as it would if it had dynamic 

 instability of route. 



(3) Be run ahead in a speed range corresponding 

 to 10.25 to 20.5 kt for the ship, 2.03 to 4.06 kt for 

 the model, to determine its general steering 

 characteristics. Maximum rudder angle and 

 maximum yaw, if practicable, are to be observed 

 but no special instrumentation need be provided 

 for this test. 



(4) Be run astern at speeds varying from to 8 

 kt for the ship, to 1.58 kt for the model, to 

 demonstrate that it will turn as directed by the 

 rudder (s). The rate of propeller rotation is not 

 limited for this test. 



78.13 Wavegoing Model Tests. A wavegoing 

 model at least 6 or 7 ft long is to be constructed 

 to the hull shape which proves superior (to have 

 the lower propeller power) in the self-propelled 

 tests. This model is to be fitted with all 'principal 

 erections above the main deck level, in block 

 form, as well as with the following appendages: 



(a) Cutwater 



(b) Rudder horn on the transom-stern model 



(c) Rudder (s) 



(d) Bower or abovewater anchor. The hull in the 

 vicinity of this anchor is to be represented rather 

 closely to scale. 



The model is to be so weighted that the longi- 

 tudinal radius of gy ration is about 0.23L, reckoned 

 about an assumed LCG of 0.505L from the FP. 

 If possible without special instrumentation, an 

 estimate is to be made of the natural pitching 

 period of the model in quiet water, for angles not 

 exceeding plus and minus 10 deg. The natural 

 rolling period of the model, for an initial heel of 

 the order of 30 deg, is hkewise to be determined 

 in quiet water. 



The model is to be towed through simple 

 regular waves by a gravity dynamometer, loaded 

 to give a constant pull as required to tow the 

 model at a speed corresponding to 20.5 kt for the 

 ship in smooth, deep water. The waves are to 

 vary in length from 0.5 to 2.5L, 255 ft to 1,275 

 ft full scale. The wave height of each system is to be: 



(a) 0.55 vLb' , corresponding to an hw = 12.42 

 ft for L,y = 510 ft 



(b) LwfiO, corresponding to an hwr = 17 ft for 

 Lw = 510 ft 



(c) Such other proportion as may appear advis- 

 able and be agreed upon before starting the tefsts. 

 The angle of encounter is to be 180 deg (ship 

 heading directly upsea), but a few runs are to be 

 made at angles of encounter of deg (foUomng 

 or overtaking sea). 



Still photographs are to be made of the model 

 at extreme up- and down-pitch positions, in 

 regular waves of a length which produce the 

 worst ship behavior. 



78.14 Vibratory Forces Induced by the Propel- 

 ler. In view of the unusual forms of the alterna- 

 tive sterns for the ABC ship, as well as the small 

 tip clearances contemplated, it would be extremely 

 useful to have some indication of the propeller- 

 excited vibratory forces to be expected on the 

 hull. However, at the time of writing (1955) the 

 instrumentation for this purpose is still being 

 developed by the David Taylor Model Basin 

 under SNAME Technical and Research Project 

 H-8. When it is available, vibration tests can be 

 included in a model test program. 



78.15 Reporting and Presenting Model-Test 

 Data. Except for the notes concerning reproduc- 

 tions of the model-test data, this section is written 

 generally in the wording that would be employed 

 in requesting this work of a large-model-basin 

 estabUshment. 



It is planned that SNAME Resistance Data, 

 Propeller Data, and Self-Propulsion Data sheets 

 will be made up (by the Design Office; in this 

 case, the author and his assistant) for the tests 

 of both models and of the special model propeller 

 built for the selected model. 



Sufficient data are to be observed and recorded 

 to enable the results to be presented in the form 

 described for the items following. The data hsted 

 are to be presented separately for each model 

 and model propeller: 



(1) Curves of effective power Pe and friction 

 power Pp , both bare hull and mth appendages, 

 for the fully loaded and partly loaded conditions, 

 including calculated values of the wetted surface 

 S for each condition. The value of ACf , as 

 previously stated in Sec. 78.6, is to be taken as 

 0.30(10"'). (Curves of effective power Pe for 

 both models of the ABC ship are given in Fig. 

 78.Nc on page 892 and in Fig. 78.1). 



