of these surveys are compared with the results of drag measurements of the 

 model under the same conditions of boundary-layer stimulation. 



BOUNDARY LAYER SURVEY OP MODEL OF AN OIL TANKER 



DESCRIPTION OP MODEL 



In order to investigate the extent of the laminar boundary -layer 

 region, a model of a full-form ship was selected for survey. A 25-foot model 

 of a 600-foot tanker was selected because drag measurements on this model had 

 given strong indications of the existence of laminar flow over a considerable 

 portion of the wetted surface. It may be seen in Figure 1 that the vessel 

 has full lines, the longitudinal prismatic coefficient being 0.753 . The de- 

 sign Froude number, T7=, is 0.208— which gives a ship speed of 17-3 knots— where 

 U is the ship speed, L is the length and g is the gravitational acceleration. 

 The linear ratio of ship to model is 24, whence, following Froude' s law of 

 comparison, the corresponding model speed is 3-53 knots. 



DESCRIPTION OF APPARATUS AND TEST METHODS 



The constant-current hot-wire technique has been applied in this in- 

 vestigation to determine qualitatively the nature of the boundary-layer flow 

 over the tanker model. The theory of the hot wire Is briefly reviewed in the 

 appendix of this report. 



As shown in the appendix a wire placed in a flow and heated by a 

 "constant" current produces a voltage drop which is a function of the square- 

 root of the velocity. Hence, velocity fluctuations of turbulence will be re- 

 flected as voltage fluctuations in the circuit. A thorough treatment of the 

 theory and application of the hot wire in air has been written by Schubauer 

 and Klebanoff . 2 



The particular electrical circuit adapted to this investigation is 

 illustrated in Figure 2a. Hot wires mounted on probes of the type shown in 

 the photograph in Figure 2b, were separately connected to 4 circuits of this 

 type. Each wire was heated by a current of 0.1 8 amp drawn from a 12-vblt 

 heavy-duty storage battery. This current, which was kept substantially con- 

 stant, was sufficient to give a wire temperature 60° P greater than the ambi- 

 ent water temperature, which over the period of testing varied between 72° 

 and 7^° P- As shown in the sketch of the circuit the voltage drop across the 

 wire was fed into a TMB Type-3A current amplifier, the output of which was 

 used to drive 4-milliampere galvanometers in a Consolidated oscillograph. 

 Galvanometer responses were recorded photographically. The responses -of as 



