through the Small Business Innovative Research (SBIR) program. At the conclusion of the SBIR 

 Phase II, the water hammer impact mechanism will be documented separately. 



Requirements 



The original design requirements for the seawater rock drill served as guidelines for this 

 impact mechanism development. Drill performance was stated as having a penetration rate 

 equivalent to the Stanley model HD-20 oil hydraulic hammer drill currently in the Underwater 

 Construction Team (UCT) inventory. This was restated for our purpose as an impact mechanism 

 capable of delivering to the drill steel and rock interface 7 foot-pounds of impact energy at a rate 

 of 30 cycles per second. At this performance level with a 3/4-inch-diameter drill bit, a 

 penetration of 3.5 inches per minute is calculated for rock having a 12,000 pounds per square 

 inch compressive strength (Ref 3). 



The prototype rock drill as-built weight was 49 pounds. Though 9 pounds heavier than 

 the design requirement, it was previously agreed that the extra weight did not detract from drill 

 operability. In the model, the drill weight was set at 50 pounds. 



Component Description 



The Pre-Production Prototype (3P) rock drill, shown in Figure 1, is configured with a 

 single poppet-kicker port linear impact mechanism. The functional description of the cycle can 

 best be understood by reviewing the diagram shown in Figure 2. 



During tool operation, water at supply pressure enters the drill through the trigger valve 

 and is directed into the drive chamber through the initially open supply poppet. This water flow 

 in turn drives the plunger and the piston down into the drill steel creating a percussive impact 

 at the rock surface. Near the end of the drive cycle, the relative position of the drive plunger 

 within the plunger sleeve causes the kicker port to pressurize and closes the supply poppet. The 

 closing of the supply poppet results in a bleed down of drive chamber pressure allowing the 

 piston return to reset the plunger. During plunger reset, the relative position of the drive plunger 

 within the plunger sleeve relieves the kicker port and permits the supply poppet to open. From 

 this point the cycle repeats. 



Exhaust flow from the linear impact mechanism is directed to the 3-horsepower seawater 

 motor to index the drill steel. Motor exhaust is discharged to ambient out the motor exhaust 

 port. 



DYNAMIC MODEL 



The software selected for model development was the Dynamic Analysis and Design 

 System (DADS). The developed computer model of the linear impact mechanism qualitatively 

 mimicked empirical test results obtained during prior rock drill evaluation testing. After model 

 validation, parametric studies were performed for comparison to baseline model results. Model 

 refinements lead to predictions of performance improvements. These improvements were 

 validated using the 3P drill to test modified impact mechanism component parts. 



The basic building blocks for the model consisted of bodies, some fixed to an inertial 

 reference frame, and some allowed to move; joints between the bodies; springs; hydraulic 



