51 



in the buoyant cable was recorded with a dynamometer inserted in the line at 

 each ship. At the highest towing speed the tension was approximately 5500 

 pounds . 



Launching of the gear was accomplished from the senior minesweeper. 

 The junior ship was brought alongside, and a line was passed from the senior 

 vessel to establish the loop. The buoyant cables were then independently 

 launched from each vessel. On the senior ship, the nonbuoyant cable and the 

 buoyant cables were launched simultaneously from a single reel on the fantail. 

 As the sweep cable was paid out, the floats were secured with a snap hook to 

 a ring wired to the cable. 



Although the specified depth of the nonbuoyant cable was 5 feet or 

 greater but not in excess of 50 feet, a pendant only 3 feet long was used. 

 The pendant was of hemp rope with swivels and eyes at each end. This short 

 length was used because, in earlier trials with the copper cable in which 

 twenty-one NMWTS floats were used, the tow became submerged and it was found, 

 on retrieving, that the cable had been dragging on the river bottom. The ob- 

 servations made during the model-basin tests of the NMWTS float, Appendix 1, 

 indicated that such an effect could be expected if only the cylindrical 

 floats were used. 



The method of securing the pendant to the floats is shown in Figure 

 39. For the TMB float the pendant was fastened to a shackle at the apex of 

 the bridle, while on the cylindrical floats the pendant was made fast in a 

 shackle welded to the apex of the cone. 



OBSERVATIONS MADE DURING THE PULL-SCALE TRIALS 



During the launching operations, one TMB float became fouled over 

 the free buoyant cable in the manner shown in Figure 40. It appeared that 

 the cylindrical floats were not as susceptible to fouling because of their 

 shape and method of towing from the nose. Prom Figure 40, it is apparent 

 that the cylindrical float requires less towline tension than the TMB float 

 in order to free itself from the buoyant cable. However, as the catenary 

 loop developed, the TMB float was pulled free of the buoyant cable and no 

 further difficulties were encountered. For this particular project, it is 

 believed that fouling can be prevented by careful launching. If the buoyant 

 cable does wash over the top of the floats in a heavy sea or in cross cur- 

 rents, it can be freed by momentarily increasing the speed. By increasing 

 the towing speed, the components of tension in the loop transverse to the 

 direction of tow and the drag on the buoyant cable can be Increased suffi- 

 ciently to pull the fouled float under the buoyant cable and free that cable. 



