I require plans to build an underwater metal detector, that can be
towed behind a boat. I can make the housing and tow cable but require
detailed plans for the internal sensor unit. I want to use the output
of the sensor unit to feed into a PC and then note abnormalities in
the magnetic field of the ocean floor that it is being towed over. I
am really looking for large metal objects in water up to 100metres
depth, the unit will be designed to be towed 10 -15 metres from the
ocean bottom.

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Request for Question Clarification by denco-ga on 29 Sep 2005 13:53 PDT

Would something such as the following fill your needs?  Thanks!

http://www.thunting.com/geotech/pages/mag/projects/fmx1/fmx1.pdf

Looking Forward, denco-ga - Google Answers Researcher

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Clarification of Question by exploring-ga on 29 Sep 2005 15:24 PDT

Hello, thanks very much for this infomation - I already have some
plans for metal detectors - but what I really need to know is how they
are built into the "towfish" that you tow behind the boat. All the
units that I have seen are housed in an approx 100mm x 1000mm round
tube with fins and a towing lug. I can make the housing unit but need
to know how the electronics are adapted to fit inside a long tude
instread of what seems the typical about water construction of a plate
size detector unit. The sensitivity is important as it needs to be
able to sense large metal object in salt water when being towed approx
10metres from the bottom. Looking at the Speake & Co FGM it would
appear that they can be mounted inside a tude - can you mount a number
of them for great sensitivity and will they detect as i require ?