response of the 8101 hydrophone is 1 Hz (-3dB). The NAGRA T recorder allows 

 this 1 Hz response to be used, since it has DC recording capability using 

 frequency modulation (FM) recording amplifiers. The upper frequency recording 

 limit using FM record at the 7% ips recording speed is 2.5 KHz. The frequency 

 range from 100 Hz to 30 KHz is covered by the direct recording amplifier. 



The first Cook Inlet platform measured was the Ocean Bounty, a 

 semi-submersible drilling rig. Ocean Bounty was located about 40 miles off 

 Homer, Alaska. It is supported by eight legs, each pair connected at the 

 lower end by a 26-foot diameter hull. The inboard hulls house the propulsion 

 motors, and all hulls are floodable for submersion at the drilling site. The 

 rig is anchored by chains at eight points on the ocean floor. Rig Ocean 

 Bounty is shown in figure 2. The major airborne noise sources aboard were 

 4-2,000 HP diesel engines, two of which are running at a time. Their exhausts 

 are unmuffled and point downward toward the water. Figure 3 shows the exhaust 

 pipes under the rig. ARCO has plans for muffling the exhaust. 



The Ocean Bounty was drilling during the period of measurement. NOSC 

 personnel were not told the drilling depth due to company restrictions. 

 Measurements were taken from the "Big Valley," a 50-foot fishing trawler 

 (figure 4). The trawler was brought close to the Ocean Bounty, it's engines 

 were shut down, the hydrophone was put in the water, and recording started 

 while drifting away from the platform. Drift runs commenced about 50-100 feet 

 from the platform and stopped at various distances ranging from 300-800 feet. 

 Hydrophone depth was varied from 20-110 feet. The wind was 15-20 knots with a 

 sea state of 2 to 3. Water depth was 200 feet. 



D-4 



