CRUISE REPORT

VESSEL:  M/V FARNELLA

AREA OF OPERATIONS:  
	Eastern Gulf of Mexico

DATES:
	Depart Tampa, FL 1000 (EDT) 2 October, 1985
	Arrive Key West, FL 0800 (EDT) 22 October, 1985

PERSONNEL:
	Roy Hadgraft, Captain
	David Twichell, USGS (U.S. Geological Survey) Chief Scientist
	Robert Commeau, USGS
	Steven Mateus, USGS
	Page Valentine, USGS, Data Curator
	Charles Paull, Scripps Institute of Oceanography
	Kim Benjamin, Woods Hole Oceanographic Institution
	Derek Bishop, IOS (Institute of Oceanographic Sciences, U.K.)
	Lindsay Parson, IOS
	Robin Bonner, IOS
	Jon Campbell, IOS
	Andrew Harris, IOS
	Colin Jacobs, IOS
	Doriel Jones, RVS (Research Vessel Services, U.K.)
	Derek Lewis, RVS

EQUIPMENT:
	GLORIA long-range side-scan sonar
	Airgun (160 and 80 cu in) single-channel seismic-reflection system
	3.5 kHz profiler
	10 kHz profiler
	Magnetometer
	Loran C
	Satellite receiver
	Global Positioning System

OBJECTIVES:
	As part of the program to study the Exclusive Economic Zone (EEZ) of 
the Gulf of Mexico, the U.S. Geological Survey, in cooperation with the 
Institute of Oceanographic Sciences of the U.K., undertook a long-range
side-scan sonar survey of the Gulf of Mexico.  The EEZ seaward of 
approximately the 500 m isobath was mapped using GLORIA (Geologic LOng-
Range Inclined Asdic), a system owned and operated by IOS.  In addition
to the GLORIA data, airgun, 3.5 kHz, 10 kHz, and magnetometer data were
collected.  During leg 3A, the final leg of the program in the Gulf of
Mexico, the Florida Escarpment and the distal end of the Mississippi Fan
were surveyed.  The cruise was 20 days long, and data were collected along
6,741 km (3,640 nm) of ship's track.  The area mapped by GLORIA during this 
leg was approximately 50,586 square kilometers (27,314 square nautical miles).

NARRATIVE:
	Leg 3A was very successful.  The weather was superb and imposed no
restrictions on the operation of the equipment.  The warm surface water
temperatures, which imposed such severe restrictions on the line spacing during
legs 1 and 2, were not as serious a problem during this leg because of the deep
water depths in which we were working most of the time.  The only area where
the surface water temperature affected the sonar's range was in the shallow
water east of the Florida Escarpment, but even here we were able to get
complete GLORIA coverage to depths of 400-1,000m.  The Loop Current in the
southeastern corner of the Gulf reached speeds of 7.4 km/hr (4 kts) and was
highly variable in its direction of flow.  This current made it difficult to
steer straight lines, and had an effect on the orientation of the GLORIA
vehicle.  The greatest challenge to operations, though, was fishing boats and
their long-line fishing gear.  The lines were as long as 65 km (35 nm) and 
were 20 m below the surface; too shallow to go over with GLORIA.  The fishing
fleet was particularly abundant in the DeSoto Canyon area, but some were
also found near the edge of the Florida Escarpment at 25dN.  The long-line
gear is the reason for the peculiarities in the ship's track in these two
areas.
	After the first two days, equipment down time was minimal and operation
were very smooth.  There were some logging problems with the GLORIA system and 
about 11 hours of data were lost at the beginning of the cruise.  Initially the
Muirhead camera (part of the system used to play back the data for building
the at-sea mosaic) was not working properly, but it was fixed and caused only
a slight delay in building the mosaic.  The preamplifier in the Northstar
Loran C antenna was damaged when we left Tampa and could not be fixed, but we
managed very well using a combination of Loran C fixes from the ship's 
receiver, satellite fixes, and fixes from the Global Positioning System when
available (6-7 hours a day).  The seismic-reflection system was down for about
9 hours during the entire cruise.  A 160 cu in airgun was used for the first 
three days, and after that we switched to an 80 cu in chamber.  The smaller
chamber resulted in much less wear on the airgun, yet still provided excellent
subbottom penetration.
	The data from leg 3A were full of surprises.  The Florida Escarpment
was spectacular, and showed a lot of unexpected changes in morphology along
its length.  Mass wasting on the slope above the escarpment was more extensive
than expected, especially south of about 26dN.  The slide or slides on the
Mississippi Fan that we started mapping on Leg 2 extend to the southeastern
corner of the Gulf (24dN).  The distal end of the Mississippi Channel was 
found at about 25d30'N-86dW, but it was filled with slide deposits which
extended much further to the south.

TABULATED INFORMATION:
	A.  Days at sea:  20

	B.  Amount of data collected:
	System			Time Spent		Km Data Collected
	GLORIA			424 hr 45 min		6,557
	10 kHz profiler		435 hr			6,734
	3.5 kHz profiler	435 hr 15 min		6,738
	Airgun			428 hr			6,578
	Magnetometer		433 hr 30 min		6,712