Underwater Metal Detector

[kintama411]

Hi,
I'm working on a project to recover a drone that fell into a lake and am in need of some help concerning metal detection. I'll be laying out the context and ask questions. If you feel like your knowledge could help, feel free to answer them or just share your thoughts with us.

Context:
The lake's water is very troubled and the depth reaches 6 meters, with seaweeds of up to 1 meter coming up from the ground. Access to the lake is on permission only as it is inside a private property, therefore the recovery operation has to be done the fastest that is possible.
The drone is either stuck in the seaweeds or sitting on top of them as it is relatively easy.
The area where the drone fell was hidden by a small island and we couldn't clearly see it, but we have a rough estimate (20m x 20m area).
Hence my club and I decided to build a metal detection system that would allow us to easily enough locate and recover the drone.
One of us can dive with an oxygen bottle, we might get a motored boat there.

As the head of this project, and because this is rather new to us, I have a few questions for those of you who could and want to help us get started.
Q1: Do you believe it is possible to use a MD to find our drone in such conditions?
Q2: If so, what do you believe is the best type of detector for this application? If not what other ways can you see?

We gathered a few ideas and got started, assuming it was.
We initially thought about designing a PI detector, that could either be in the water, hauled by the boat, and transmit or store digital data and position (with wifi antennas allowing for triangulation of the position).
But then we thought that prototyping a basic BFO detector would be the easiest way to get started as its way of working is really simple and there is no need for components other than r, c, l and a few npn.

So this one is on its way to be tested this week (simulations seem to work). It would be waterproof and hand held by the diver. The detection would be purely analog and feed into earphones.
Q3: Would this be good enough, with high enough reach? (>1m)
Q4: What do you think of the first idea?
Q5: Do you have other ideas, or experiences that could allow us to get this project on good/better tracks?

Thank you for your attention,
Clément

[WM6]

Better invest in new drone than in detecting equipment.

[Qiaozhi]

Presumably the drone contains very little metal, so detection with a homebrew BFO detector at 1m (or beyond) will be highly unlikely.
As your primary goal appears to be recovery of the drone, I would suggest purchasing a second-hand underwater PI detector, especially since one of your team is a diver. Unless, of course, you're especially interested in the recovery being made with a DIY design. Alternatively, you could construct either a MiniPulse Plus, Surf-PI or Baracuda kit from Silverdog. Any of these would be far superior to a simple BFO.

http://www.silverdog.co.uk

[kt315]

this is an job not for the MD.

A1: drone metal mass is so small your issue is not bringing a perspective on 6 meters depth.
A2: try scuba diver equipment in good sunny day.
A3: buy a color camera on a cable - them much on aliexpress, for fishing - they are not so expensive.

[kt315]

[kt315]

[Thomas]

I would suggest a drag line, kind of like this

[kt315]

would suggest if you get out a drone above water to attach at its top some piece of a styrofoam. and Lo! Voila! your
drone will swim like a popup bobber!

[kt315]

[sinclairuser]

the biggest faux pas in your OP was admitting you dont have permission from the access holder, permission from the drone owner is not enough i'm afraid.
iv'e had this argument with people who have asked me to find lost objects, they seem to think because its their lost property i can detect anywhere they might have lost an item.
sorry it does not work that way, you need permission from both landowner and the person who lost an object, the sad fact is when you tell landowners about a lost item of value, they almost never give permission.
in the case of wedding rings insure them, and if you lose them away from your own land forget it and claim, honestly its less hassle.