STRAIGHT-LINE TOW 



For the straight-line tow boom towing configuration the force, F , 

 acting on the boom, is given by the frictional drag on the skirt, i.e., 



Fq = Cp pv^ hL (A-6) 



where C„ = friction coefficient 



F 



h = boom skirt depth (ft) 



V = tow speed (ft/sec) 



L = length of the boom (ft) 



The value of Cp is dependent on the Reynolds number, R = V L/u, 

 where u is the kinematic viscosity (1.09 x 10" ft^/sec for seawater). 

 It is noted that for a 1,000-foot length of boom the value of the 

 Reynolds number is over 10^ and the condition for straight tow is 

 always turbulent . 



In particular, at a tow speed of 10 knots, R = 1.6 x 10 , 



C_ = 0.0015, and Equation A-6 yields 



F 



¥^ = 854 h (A-7) 



Equation A-7 was used to estimate the drag force on 1,000 feet of boom 

 in a straight -line tow for each of the three boom types. The results 

 are shown in Table A-2. It should be noted that the estimate given by 

 Equation A-7 does not include the effects of unsteady forces caused by 

 towing through the complex wave spectrum of an actual seaway. Limited 

 data recorded in April 1972, during a field-acceptance test of boom of 

 the same size as Tjrpe II indicated a towline force of 2,800 pounds 

 when towing at 10 knots. 



In any event, since the force loadings are much higher in catenary 

 tow, they were used in the structural analyses described in Appendix B. 



ANALYSIS OF TRANSVERSE HYDRODYNAMIC LOADS ON A BOOM CONNECTOR 



For sound structural design the boom-end connectors must be sized 

 to accommodate transverse hydrodjmamic forces that are placed on the 

 connectors when a boom is being towed in a catenary configuration (Fig- 

 ure A-1) . A model that can be used in sizing connectors and an estimate 

 of the magnitude of transverse hydrodynamic forces are determined 

 below. Calculations are made for a connector located at the center 

 of a boom catenary. 



36 



