Sec. 7S.7 



MODEL-TESTING PROGRAM FOR A SHIP 



Fig. 78.B TMB Model 4505 at a Speed Corresponding to 20.5 kt for the Ship 

 The subscript "W" following the TMB model number on the legend signifies that the model is made of wax. 



namely 20.5 kt. This range corresponds to about 

 6 through 22.5 kt for the ship; 1.18 through 4.46 

 kt for the model. The reason for the emphasis on 

 the low-speed range is to: 



(1) Determine the deep-water resistance cor- 

 responding to the low speeds necessary for the 

 ABC ship in the canal leading to Port Amalo and 

 in the river leading to Port Correo 



(2) Determine rather accurately, in the bare-huU 

 condition, the separation drag in the range below 

 that at which wavemaking occurs. 



Even though stimulation may be considered 

 necessary by the David Taylor Model Basin to 

 insure turbulent flow over practically the entire 

 area of the model hulls it is desired that, if 

 practicable, some resistance measurements be 

 made in the low-speed range without turbulence 

 stimulation of any kind. 



The shell plating at both ends of the ABC ship 

 is to be welded, with butts and laps both flush. 

 For the remainder of the length the strakes of 

 plating are to be raised and sunken, with welded 

 butts and riveted seams. All excrescences are to 

 be kept to a minimum, and fairmg is to be careful 

 and thorough. A type of bottom coating is to 

 be used that is either self-levehng or inherently 

 smooth. It is beheved, therefore, that a roughness 

 allowance AC;? of 0.30(10"^), to be applied to 

 the ATTC 1947 or Schoenherr friction values, is 

 ample to represent the new, clean-bottom con- 

 dition of the ship. 



The usual photographs of both models under 

 the towing carriage are to be taken, at zero speed 

 and at speeds corresponding to 20.5 kt for the 

 ship, 4.06 kt for the model, first when run bare 

 hull, without the cutwater, and then when run 

 with all appendages. 



Figs. 78.A and 78.B are reproductions of the 

 photos of the transom-stern model, at zero speed 



and at a speed corresponding to the ship trial 

 speed of 20.5 kt. The lower can-iage platform 

 furnishes a reference for estimating visually the 

 sinkage and trmi (by the bow) when underway. 



78.7 Wave Profiles and Lines of Flow. Wave 

 profiles and lines of flow are to be taken on both 

 models, bare-hull condition, at a speed corre- 

 sponding to 20.5 kt for the ship, 4.06 kt for 

 the model. The wave profile is to include the 

 profile across the transom. (See Fig. 66. R). 



For all resistance and self-propulsion tests the 

 model speeds are to be noted at which the transom 

 clears; in other words, when the entire area of the 

 transom is exposed to the air. Undoubtedly this 

 will be different for the two types of stern. If 

 necessary to determine this clearing speed the 

 model is to be run faster than that corresponding 

 to 22.5 kt. (See Sec. 78.19). 



It is desired that the lines-of-flow observations 



Fig. 78.C Bow-Quarter View of Transom-Stern 

 Model Showing Lines of Flow by Chemical Means 

 The photograph is inverted to afford better visualization 

 of the flow. 



