The lifting frsutie and base plate are attached to the concrete block 

 at the center by a one-inch diajtneter brass anchor rod xjhich is insulated 

 from the steel base p3ate with l/8 inch hard gaskets between the plate 

 and the brass washers. A rubber or Plexiglas sleeve is placed around the 

 anchor pin to prevent electrolysis « The ferass anchor rod in turn is 

 secured at the bottom of the concrete block by a 5/32-inch brass shear 

 pin designed to shear at about an 1,800 pound pull. Thus, if the in- 

 stallation should sand up, a pull of 2,000 pounds will shear the pin, re- 

 leasing the concrete block and making it possible to recover the pressure 

 head and frame. Sufficient recorder cable is stored in a cable well, 12 

 inches in diameter and 6 inches deep in the concrete block, to allow the 

 pressure head to be brought to the surface if the cable is also sanded 

 over. 



If the buoy should be lost and the recovery chain cainot be retrieved, 

 the unit can be lifted by a 3/8 inch steel cable 100 feet long, taped 

 along the electric cable and secured to the lifting ring on the triangular 

 frame. About 5 feet of vslack is provided in the electric cable between 

 the last taping to the steel cable and the slot to the concrete anchor 

 block (Figure 2) to prevent breaking the electric cable when a strain is 

 put on the steel cable. The steel cable is retrieved from the bottom by 

 under-running the electric cable from the shore or by grappling for it 

 shoreward of the pressure head position. 



Three outer anchor studs in the concrete block prevent the base 

 plate from turning on the concrete block. During handling, the load 

 is taken off the shear pin by screwing nuts on the studs. 



Sixty feet of cable are supplied with the pressure head, but more 

 cable may be added if required. The added cable must be waterproof j 

 must have sufficient strength to withstand the physical stress en- 

 counteredj must not have such resistance as to affect unduly the output 

 of the pressure head. Tests have indicated that ordinary 2-conductor 

 cable of No, II4. gage copper wire will decrease the overall sensitivity 

 of the gage about 1 per cent per mile of cable. In adding cable the 

 conductors should be soldered, underwater splices water-proofed, and 

 all tension s trands tied so that the cable will have as much mechanical 

 strength as the uncut cable. The junction of the recorder cable with the 

 pressure head should also be thoroughly taped as an extra precaution. 



The MH-1 underwater pressure gage is normally placed on the ocean 

 floor in 10 to UO feet of water some 1,500 to 6,000 feet offshore. The 

 electric cable is run on the bottom from the pressure head shoreward 

 through the surf zone to the recorder placed in a building near the beach. 

 For temporary installation the gage can be used without the concrete block 

 by mounting the pressure head tripod directly on the base plate. The con- 

 crete block can be replaced by a steel base plate of equivalent underwater 

 weight, but if this is done the legs of the pressure head tripod and the 

 lifting fraiTie should be lengthened 10 inches in order that the pressure 

 head will be the proper distance above the bottom. 



