Geometrics G-882 User Manual

Geometrics Inc. G-882 Cesium Marine Magnetometer Page
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2. Neatly lay the cable out in long loops bow to stern on the deck
beginning with the onboard end. As this is done remove any twists in
the tow cable. The cable may be deployed from the loops on the deck
without knots and kinks. One person should be assigned to walk the
loops back on the deck during retrieval. This method works well with
cables up to 60m (200 ft).
Tow cables longer than 90m to 120m (300ft to 400ft) should probably be
handled with a winch.
Manual deployment, is best handled with two people, especially when
additional depressive weights are being used, a third person should manage
the tow cable. The vessel should be making 1 to 1 ½ knots during deployment.
It may be necessary to increase the vessel speed as more cable is deployed to
prevent the magnetometer from striking the bottom. The more quickly the
desired cable length can be deployed and the desired tow speed attained
reduces the chances of the magnetometer going too deep striking the bottom or
becoming hung. The recommended cable management mentioned above will
aid in quick deployment. Another method is to stop playing out tow cable a few
times during deployment while under tow. This will allow the tow fish to rise
towards the surface. If a CG towed fish with a depressor wing is being
deployed, it pulls with significant force. It may require two or three people to
hold it during the play-out stops.
It is best if the tow cable is tied to the vessel before the vessel begins to acquire
the desired tow speed. The magnetometer with the depressor wing produces
strong pull forces under tow speed of 4 to 6 knots.
Determine the approximate length of tow cable to be deployed to achieve the
required survey depth. We recommend that the Kellems grip provided on the
tow cable be used to secure the tow cable to the towing vessel. Slide the
Kellems grip to set the length of tow cable desired to be deployed plus some
additional cable to account for the distance from the ship to the cable water
entry point. Secure the Kellems to the tow cable as shown in Figure 43. DO
NOT tape along the whole length of the Kellems; this will prevent it from
working properly. Attach the Kellems to the towing vessel using a strong line
tied to the loop of the Kellems grip.
A Kellems grip is like a child’s toy finger trap. The stronger the forces that pull
on it, the tighter it grips the cable. If the Kellems grip needs to be moved to
adjust the amount of tow cable deployed, remove the tape anchoring it to the
tow cable and compress each end to the Kellems towards the other along tow
cable. This will expand the Kellems and allow it to slide easily along the cable
to its new position. Release the ends of the Kellems, re-anchor the end
towards the towfish as shown Figure 43 and then smooth it back down along
the cable towards the vessel.

Geometrics G-882 Specifications

General

Brand	Geometrics
Model	G-882
Category	Marine Equipment
Language	English