FARALLON ISLAND SURVEY

After CURV recovery had started, the fathometer was shut down and logging of the fixes stopped. However, the RPS was kept on and

continuously

monitored in the event that the CURV lifting line

and cable parted and the vehicle lost its positive buoyancy. Thus, its precise location would be known for subsequent

The Gifft recorder was operated approximately through the same period as the RPS logging. For the depth range of 700 to 1000 meters over most of the surveyed area, the most convenient full-scale range was 300 meters (1.5 mm = 1 m) with depth graduations at 20-meter intervals. Thus, depths to within five

meters could be read with a quick glance, to within two meters with normal "eye balling" and within on e meter using multiple dividers. The best trace, during CURV operations, was obtained using a gating program of three transmitting pulses followed by three receive/write pulses at a gain of 10. Gains of 20 to 100 were required when the ship was backing or during the bathymetric survey when the ship's speed was five knots. feed rate of 2 cm per minute was adequate for resolution even over the rough bottom at the five-knot survey speed. During the one-to-two knot transit speeds and station keeping periods, this feed rate was maintained.

special

A paper

Trying to save paper by slowing the

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FARALLON ISLAND SURVEY

feed rate caused the wet process paper to dry out under the moving stylus and wrinkling resulted.

As could be expected, the contouring on the published charts was highly generalized compared to what may be plotted at a scale of 1:25,000. For example, the 500-fathom survey area is shown On NOS Chart 5402 as a very broadly rounded nose, gently plunging to the west between two intermediate-sized sea-valleys. Because it was shown to be one of the smoothest areas on the upper continental slope of central California, no problems were anticipated in making CURV transits or operating the sonar in any direction desired. This area actually is a series of ridges and gullies with slopes up to 30° and numerous ledges and mounds with local relief exceeding 40 meters. A special bathymetric chart, at a scale of 1:10,417, with a contour interval of 10 meters, was prepared from the bathymetric and navigational data. This chart is presented as Figure 4-2.

The first phase of the daily operation was to determine drift rate and direction of the ship. This was done because during the launching of CURV, the M/V Gear must not turn its screws for a period of five to fifteen minutes while CURV is driven around the stern and up to the bow of the ship. The drift rate and direction was determined by plotting a series of precision

fixes

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FARALLON ISLAND SURVEY

at

five-minute

with the ship lying dead in the water.

to

the

intervals for a period of one-half hour or more, During the survey period, the drift ranged from 0.5 to 1.0 knots and was generally Southeast. With this information, a launch point was established fifteen minutes updrift of the selected bottom target site.

In future launches of the CURV from M/V Gear, this procedure of obtaining drift rate and direction, and determining a launch

point updrift from the target point may be minimized because of the following factors:

1. The CURV vehicle and its cable act as a sea anchor launching and the drift rate is approximately

2.

after

half that of the ship alone.

The ship is headed into the wind and sea at the start of the launch and several minutes elapse before it falls off and lays broadside to the wind. Thus, the full effect of the wind is not felt during this

interval.

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Section 5

SHIPBOARD RADIOANALYSIS

The EPA office of Radiation Programs --Las Vegas Facility (ORPLVF) and the Environmental Monitoring and Support Laboratory, Las Vegas (EMSL-LV) provided shipboard radiation monitoring and measuring services. These included radiation monitoring

of the

CURV and associated equipment upon recovery from each dive and counting of sediment samples for radioactivity.

Personnel radiation dosimeters were provided for all personnel involved with handling the CURV who could conceivably be exposed to radiation from recovered samples. Conventional beta-gamma film dosimeters were provided by NUC for the deck crews and a thermoluminescent dosimeter (TLD), provided by EPA, was worn by The Murphy Pacific diver. No personnel radiation exposures above expected background were recorded for any individual on the project.

The radiation monitoring and counting equipment carried on the M/V Gear for the project are described in Section 3.3 of this report. Figure 5-1 illustrates the temporary laboratory was installed in the ship's carpentry shop.

which

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79-747 O-77 - 12

5-1