< -2 - 



40 60 

 TIME IN SECONDS 



80 



100 



Figure 2 , 



Plot of Free Spar Oscillations 

 From Initial Displacement 



Spar Specifications 



The spar pole is assembled from the following components: 

 1. 76 ft of 5 in. nominal diam, schedule 40, 6061-T6 



aluminum pipe, 



10 ft of 3 in. diam, 7075-T6 aluminum tube with 

 0.250 in. thick wall. 



20 ft of 2^ in. nominal diam, schedule 40, 6061-T6 

 aluminum pipe. 



10 couplings and 2 caps specially made from 

 6061-T6 aluminum, with straight continuous threads, 

 0-ring seals and bulkhead partitions. (Fig. 3) 



All components of the spar are capable of withstanding the 

 pressure of submersion to at least 1000 ft as well as the 

 bending stresses as a result of handling. Couplings with straight, 

 continuous threads are required for the stress level created by 

 bending, even though they take considerable time to assemble. A length 

 of 7075 -T6 tube was used for the reduced portion immediately above 

 the spar step because this area is highly stressed by the flexing 

 action when the spar is partially erected. (The 7075-T6 tube is 

 roughly twice as strong as 6061-T6 but is harder to obtain and is 

 not as corrosion resistant.) To facilitate handling on board 

 ship>the top 30 ft of the spar can be removed quickly by separ- 

 ating the reducing coupling at the transition zone. That 

 coupling is held together by four studs. Overall length of the 

 spar pole is 106 ft with a normal trim of 16 ft above the neutral 

 water line. Gross weight is 480 lb with a net buoyancy of 430 lb. 



171 



