The rock projectile. Including fluke and piston, is shown in 

 Figure 6. The piston is 26 inches long and weighs 115 pounds. The 

 piston is not fixed to the fluke shaft; it fits over the shaft and can 

 separate during penetration. Constructed in the chosen three-fin con- 

 figuration, the fluke is about three feet long, has a two-to-one taper 

 to the nose and weighs 160 pounds . With connective gear the total 

 weight of the rock projectile is 300 pounds. One-inch-thick, 100 ksi 

 yield (4140) steel is used for the plates and center shaft while 160 ksi 

 yield (4340) steel is used for the fluke nose. The nose has a length- 

 to-diameter ratio equal to three because this was found to be the most 

 efficient rock penetrating shape (Young, 1970). The nose must remain 

 intact during impact to properly fracture the rock to allow the weaker 

 three-fin portion to penetrate without damage. Ideally the nose should 

 have a very high yield stress and a low modulus of elasticity (Feltz 

 1970). Since these are opposing requirements it would have been diffi- 

 cult to arrive at a suitable balance between modulus of elasticity and 

 strength without testing. Another alternative is to use high strength 

 steel with a high modulus of toughness (Feltz, 1970); 4340 steel was 

 chosen to satisfy these criteria. The nose-tip was blunted at l^g inches 

 from what would have been the tip at an included angle of 100° to elim- 

 inate tip bending or hooking during penetration. 



The fluke as mentioned is about three feet long, and the point of 

 cable attachment is about two feet above the tip of the fluke. The 

 dimensions were partially predicted on anticipated penetration depths 

 in basalt. Though available penetration formulas were derived from 

 tests on uniformly-shaped penetrometers , they can be used to bound the 

 problem. Penetration using the Poncelet equation modified by Petry 

 (Christians, 1967) and using the Sandia empirical equation (Young, 1967) 

 is estimated to be between two and eight feet in basalt. It appears 

 that load will always be applied at or below the seafloor, thereby 

 minimizing bending stresses. Another design consideration was that 

 projectile acceleration be less than 2,000 g's to reduce stresses in 

 the down-haul cable and connective gear. A projectile weight of 300 

 pounds satisfies this criterion. To maintain structural integrity, 

 remain within the weight limitation and use the three-fin configura- 

 tion, about a three-foot-long fluke was required. 



Launch Vehicle 



The launch vehicle. Figure 2, consists of a launching system and a 

 reaction vessel. The reaction vessel is composed of a 2^2- inch-thick 

 plate welded to a 19-inch-long, 20-inch-diameter, steel pipe. It is 

 attached by bolting to a bearing plate that is threaded on the breech 

 end of the gun. 



The anchor gun performance is improved by increasing the ratio of 

 launch vehicle mass to projectile mass. A point of dimenishing returns 

 is reached when this ratio is about three. The mass of the reaction 

 vessel was made great enough to give a 3-to-l ratio between the launch 

 vehicle and the clay projectile, thereby giving an even larger ratio 

 with the sand and rock projectiles. Trapped water further increases 



