Navigational Aids 



Two radar reflectors were mounted on top of the spar for 

 station-keeping purposes. One was a portable lifeboat re- 

 flector and the other was a small, stainless steel, "Sea Me" re- 

 flector manufactured by C. M. Murray Instrument Company. To 

 facilitate visual observation during the day, the top 30 ft of 

 the spar was painted with high visibility orange paint. For 

 night observation, two fishnet, marker type, flashing lights were 

 used/ one on top of the spar and the other on the recovery buoy. 



Excitation Forces 



The interaction of a multitude of forces, which change with 

 every different sea state and internal current structure, will 

 have many varied effects on the spar system. Usually, in an 

 attempt to understand basic reactions, many of the forces are 

 either assumed linear or are neglected because of relative 

 magnitude. The number of components added to the system described 

 in this report greatly complicate an analysis for an ordinary spar; 

 therefore^an attempt has been made to isolate the major driving 

 force. Experience with the spar tends to indicate that this main 

 driving force is due to the pressure fluctuation against the step 

 area . 



If a spar is of constant diameter a passing wave will create a 

 change in buoyancy proportional to the attenuated pressure varia- 

 tion on the spar bottom. This pressure fluctuation can be esti- 

 mated for different sea states by the equation:-^ 



P = p e-27rZ/L 



o ^ ' 



where P = attenuated pressure fluctuation at depth Z 

 Pq= pressure fluctuation at the mean surface 

 L = length of surface wave. 

 e = spar draft 



Using a sample Sea State 6: 



Significant wave height = 13 ft 



Average wave length = 164 ft 



Spar draft Z = 90 ft 



Sea water pressure per foot of depth = 0.444 lb/in. 2 



^ 13 ,„ ,.., -27r(90)/164 

 P = -^(0.444)e 



= 0.093 lb/in. 2 

 This pressure fluctuation, P, multiplied by the area of the 



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