APPENDIX 2 



TMB PLANING FLOAT AND NMWTS FLOAT APPLIED TO 

 A CATENARY MINESWEEPING ARRANGEMENT 



ORIGINAL SPECIFICATIONS 



The original specifications for the catenary mlnesweeping project 

 were based on the problem of towing a symmetrical loop of aluminum cable, 

 l800 feet long and 1.75 inch in diameter, weighing about 1 A pound per foot 

 in air and having a negative buoyancy of 0.55 pound per foot in sea water. 

 Required towing speeds varied from 2 to 9 knots with the two ships on paral- 

 lel courses and 330 yards apart. The maximum working tension of the cable 

 was 6000 pounds. 



To avoid touching the bottom at low speeds in shallow water, it was 

 desired to support the loop by floats attached at intervals along its length. 

 At the lowest speed of 2 knots, it was required that the floats be designed 

 so that the maximum depth of the cable would not exceed 30 feet. At no speed, 

 however, was the depth to be less than 5 feet. If a float small enough to be 

 handled manually was found to be adequate, its weight was not to exceed' 75 

 pounds. If a larger float to be handled by a crane was required, its weight 

 was not to exceed 200 pounds. 



The first design based on these specifications was the TMB planing 

 float described in the body of the report. With a sweep cable weighing 0.55 

 pound per foot in water, enough floats were required to carry a load of about 

 990 pounds at the minimum speed of 2 knots. Although the TMB planing float 

 is designed to develop dynamic lift in addition to its reserve buoyancy at 

 sufficiently high speeds, the minimum float size was based on the reserve- 

 buoyancy requirements for the lowest specified towing speed. These condi- 

 tions resulted in a preliminary design utilizing eleven TMB planing floats. 

 The towing arrangement under these conditions is shown in Figure 1 ; the 

 floats are secured to the nonbuoyant cable, and the two free tails are 

 buoyant . 



As outlined in the body of the report, the balsa-wood displacement 

 float was subsequently designed for this project on the basis of a saving in 

 weight. The NMWTS float was submitted for test on the basis of simplicity 

 of construction. 



Pull-scale trials of the TMB planing float were scheduled before a 

 request for the balsa-wood float had been received. For these trials, twenty 

 planing floats were fabricated in the Taylor Model Basin shops. However, a 

 much heavier cable was used during the trials than the aluminum cable origi- 

 nally specified. This necessitated the use of several NMWTS floats, which 



