Geometrics G-877, Operation Manual

Page: 14 / 49

Later we will deploy the tow system with Magnetometer Fish into the water. Know in advance
the depth of water into which you are deploying the tow system as catastrophic loss may occur if
the fish is snagged on the bottom or coral head. Typical tow depths at 5 or 6 knots are 5 % of the
deployed cable. Therefore, a 60 meter cable will tow the fish at approximately 3 meters at 6
knots.
Tow cables up to 200 feet (60m) in length may be
deployed from the tow vessel by hand. Deployment
of cables exceeding 200 feet in length should be
accomplished with a winch. If a hand deployed
cable is used, it should be securely tied off to the
vessel structure or well secured with a Kellems grip
to prevent damage to the tow system connector or
the Junction Box in the event the fish impacts the
bottom.
After installing the system as described above, turn
on the power via the On/Off switch on the Junction
Box and boot up the Logging Computer. Turn on
and configure the GPS for GGA NMEA 0183
transmission. A differentially corrected GPS will
give much more accurate positions (0.6 meters) than
non-differentially corrected GPS data (10 meters).
ATTENTION !
BEFORE CONNECTING ANY OF THE
CONNECTORS TO THE
G–877 MAGNETOMETER, MAKE
SURE THE CONNECTORS ARE DRY
AND SALT FREE. USE A SMALL
AMOUNT THE SUPPLIED SILICONE
GREASE LUBRICANT OR SPRAY ON
ALL MALE CONNECTOR PINS
BEFORE ATTEMPTING TO MATE
THEM. DO NOT PACK THE FEMALE
RECEPTACLES WITH GREASE, THEY
ARE NOT VENTED.
After a short period the G–877 will automatically start to send data to the Logging Computer
over the RS-232 serial interface. Start
MagLogLite

or other logging software. Follow
instructions in MagLogLite

Software Manual for setting up proper communications. In
general, using MagLogLite

Configuration Wizard will result in a quick and flawless system
setup of the G-877 and GPS communications and display.
2.4 G–877 Installation Hints.
The G–877 Magnetometer Fish, as in other magnetometer systems, is sensitive to interference
from A.C. or pulsed sources. Normally the sensor is deployed far from any electromagnetic
source, i.e. many meters behind the tow vessel. Even though the communication from the
magnetometer is essentially immune to ship borne interference, it is always good practice to
minimize the possibility of interference. Sources to avoid with magnetometer cabling include
motors in winches, tuggers and capstans, hydraulic pump power packs and engines with spark
plugs.
The power to operate the magnetometer system must be isolated from all ground connections
except one ground connection to the hull or to sea water (or no connection as may be
14 G–877 MARINE MAGNETOMETER OPERATION MANUAL