spar Dottom, A, gj.ves an approximation of the force created by the 

 change in buoyancy due to the wave . 



F = PA 



= 0.093(24.4) (3) 



= 2.27 lb. + friction 



The magnitude of this force is not large enough to validate 

 neglecting drag and friction forces. However, the same calcula- 

 tion made for the pressure change against the step area, on the 

 spar dealt with in this paper, gives a much larger force for the 

 same wave. 



P = P e-2-Z/L 

 o 



= (2.89)e-2-(l^)/16^ 



= 1.69 lb/in 



2 



^ = P (bottom- Vp) 

 = 1.69(24.4 - 7.1) 



= 29.2 lb. 



The motion caused by this downward force is of course resisted 

 by increased buoyancy: k.^ in^ x 0.M4-U Ib/in^/ft = 2.l8 lb/ft. This 

 force opposes most of the neglected forces in direction, and the 

 magnitude Is large enough so that one can assume this to be the main 

 driving force. One must remember that this force Is approximate and 

 It Is dlff ic\ilt to evaluate how much the spar motion would be reduced 

 by a smaller step area without testing. The best approach would 

 probably be to design with a smaller step area and have It much deeper 

 at possibly half the draft. This would allow the spar to operate In a 

 null zone for waves of expected sea state where downward force on the 

 step would be nearly balanced by the upward force on the bottom. 



FIELD EXPERIENCE 



Shipping and Assembly 



The volume of the spar system, including pipes, pipe fittings, 

 virtual mass containers, ballast weights, cable, chain and navi- 

 gation aids is about 35^ ft. All of the disassembled lengths of 

 the spar are less than 10% ft long, so that shipment by most 

 conventional means is possible. The total shipping weight is 

 roughly 730 lb. From the shipping configuration two men can 



174 



