11 



TEST RESULTS 



The pins inserted in Buoy 1 tend to increase the drag slightly, as 

 can be seen in Figure 14. 



The bail when fastened to Buoy 2 definitely increases the drag, as 

 shown in Figure 15- 



An interesting effect may be seen in regard to Buoy 3. At low 

 speeds up to 5 1/2 knots the bail causes an increase in drag, but from 5 1/2 

 to 9 knots it leads to a decrease; see Figure 16. 



The full-scale model of Buoy 1 with fins was towed for drag meas- 

 urements; the results are presented in Figure 17. 



The drag data obtained from tests on the full-scale model of Buoy 

 1 and the computed full-scale data as obtained from test data of the 1/3- 

 scale model are compared in Figure 18. Drag data of the full-scale model of 

 Buoy 1 include the drag of the fins. 



During the stability tests of the full-scale model of Buoy 1, the 

 buoy oscillated from side to side at the end of the towline in a plane nor- 

 mal to the direction of motion. As the speed increased, the period of oscilla- 

 tion decreased. There apparently was no pitching oscillation. It is interest- 

 ing to note that the period of oscillation of the buoy is very nearly the same 

 as that of a cylinder. The observed periods of lateral oscillation of the buoy 

 are compared in Table 1 with the computed period of oscillation of a cylinder. 



TABLE 1 





Oscillation of Buoy 1 



Speed Knots 



Period of Buoy 



Oscillation 



seconds 



Period of Cylinder 



Oscillation 



seconds 



1 .0 



5-30 



4.80 



2.0 



2.00 



2.40 



3.0 



1 .50 



1 .60 



4.0 



1 .00 



1 .20 



5-0 



0.90 



O.96 



The period of lateral oscillation of the full-scale model of Buoy 

 1 when towed at the end of a short section of towline from an underwater 

 towpoint is compared with computed values for a cylinder towed with its axis 

 normal to the stream. If the same value for the Strouhals number is assumed 

 for the buoy as for a cylinder of the same diameter, the period of oscilla- 

 tion of the cylinder can readily be computed. A free cylinder in a stream 



(Text continued on page 16.) 



