For a catenary tow at 2 knots, the largest forces occur with the 

 Type II boom. Using the tensile load of 13,600 pounds, from Table A-1 

 and the same data for angles and drag coefficient as above, the required 

 area, A, becomes 



A = 244 ft 



(B-8) 



Thus a realistic paravane is clearly inadequate to counteract the 

 vertical component of the towline force for Type II boom at the low 

 speed of 2 knots. For the smallest Type I Class 1 boom in a catenary 

 tow the required area is 2.7 ft"^. Keeping the towed boom end from rising 

 up under the action of the vertical force component and then lying 

 over is more important in the catenary sweep mode than in the straight - 

 line tow since only in the catenary sweep mode is oil being contained. 

 Since the paravane areas determined for this operating mode are quite 

 large, even for the small Type I Class 1 boom, it was decided that 

 no paravanes were to be used and this mode of failure avoided by main- 

 taining as long a scope as is necessary to prevent the boom end from 

 being pulled out of the water to an unstable roll condition. 



The structural analysis of the tow assembly is based on the free- 

 body diagram of Figure B-4A. The vertical strut of Figure B-4B is 

 considered as a beam rigidly supported at its ends with the uniform 

 load, Fg, along its length. The equation for deflection at the center 

 of such a beam is 



1 

 384 



EI 



(B-9) 



where Y = maximum deflection at center of beam span (in.) 

 max 



F = load imposed by boom (lb) 



o 



Z = length of strut (in.) 



E = modulus of elasticity (psi) 



4 

 I = area moment of inertia of beam cross section (in. ) 



In addition, the maximum fiber stress on the outer surface of 

 the strut due to the applied bending load, F , is given by 



£C 



24 I 



(B-10) 



where a = maximum fiber stress in strut 



max 



C = distance from neutral axis to outer surface of strut 



43 



