Need a large underwater coil

[erniel29]

I'm new to this forum, and metal detectors as a whole. I'd like a large coil that I could drag along a flat sandy bottom for extended range searches. I'm hoping it's possible to use an off the shelf metal detector where the electronics would be on the boat, cabled to a large coild that would be dragged along the bottom.

Sorry if I'm over simplifying the task. Just looking for suggestions.

Ernie

[Tinkerer]

I'm new to this forum, and metal detectors as a whole. I'd like a large coil that I could drag along a flat sandy bottom for extended range searches. I'm hoping it's possible to use an off the shelf metal detector where the electronics would be on the boat, cabled to a large coild that would be dragged along the bottom.

Sorry if I'm over simplifying the task. Just looking for suggestions.

Ernie

Hi Ernie,

There are dedicated metal detectors for that purpose. I think JW Fisher make one model.
A Google search may find other manufacturers.

The cable of "off the shelf metal detectors" can not be made longer than a few feet.
How deep do you want to search?

One possibility would be to have the electronics on the bottom in a waterproof housing and only send the signal up to the boat.

How wide a swath do you want to cover?

What are the targets you want to detect? how small?

Tinkerer

[bernte_one]

sounds that you search a large frame coil
should work with pulse induction detectors
but keep attention you need a pi machine which works in no motion mode
(would be heavy to sweep a big coil under water)

for the coil put some windings of wire in a small water pipe frame and fill the rest with glue so that the coil sinks down to ground
the connection cable could be glued in the frame too the other side should be over water in boat you say should be possible
i could draw it but lets work your imagination it gave better pictures
the result should look like this (look picture) maybe something bigger 2*1m for example

[erniel29]

Thanks for the quick reply. I'll be searching no deeper that 40 ft, but mostly in 20 ft of water. I would be looking for coins under about 6" to 12" of sand. I would want a search swath of about 5 ft wide. I've looked at JW Fishers, and their Proton and Pulse mags are great for finding iron cannons and such. Basically I want to avoid diving into the water and hand searching, until I've had a hit with this device. One other though of mine would be to take multiple detectors and lay the coils side by side in a PVC frame. The frame would hold the coils about 3" above the bottom. Again, I don't know how long I could extend the cables.

[erniel29]

Wow, this is exactly what I need

Thanks
Ernie

[erniel29]

Hmmm, I checked out their website. Don't know if it will work underwater, or how long the cable can be. I sent them an email.

[Tepco]

Finding coins whit something capable for 5ft wide swath may look like " Harry Potter design challenge", however, US4912414 may contain useful coil design idea for this purpose.

[Monolith]

60ft cable
5ft x 3ft coil
12V battery consumption 2A continuous
Detects a 1 Escudo gold coin at 40 cm
Detects a 1 Reale silver coin at 40cm
Detects a 8 Escudo gold coin at 80cm
Detects a 8 Reale silver coin at 80cm

Detects a 5 ft wide swath in 50ft of sea water.
It is a "motion detector", meaning it only detects while in movement, like towing or up and down movement.

Will this do the job?

Monolith

[erniel29]

Yes that would work just fine, where can I get one?

[Monolith]

This is not a "off the shelf detector". It is designed and built for a specific task and for a specific environment.

Could you give some more information about your working environment and detecting goals?

Monolith

[erniel29]

Operating environment is in shallow water, 20 to 30 feet, dragging coil from a boat along a sandy bottom, searching for coins, or other metal artifacts.

[erniel29]

JW Fishers Pulse 6x or 8x PI detectors have an optional underwater connector for attaching different coils. They have 2 options, one is an 18" round coil with 100' of cable for boat deployment, and an 8" x 48" coil on a draggable skid with 100' of cable.

Exactly what I was looking for!