I also buildt a quick and dirty water detector.
I just opened an old damaged electronical scale and soldered the needed parts out. You cant see those small smd parts, but they are there 
1: 10kOhm resistor
2. buzzer
3. npn transistor
4. sensor cables attached to the basis of the transistor.
As soon as one of the cables are in water, current can float into the basis and the buzzer gets activated. It works fine. But I havent built in the board yet.
Coming to the first test run.
The board overall worked fine.
A bit of rework is needed, because the controll unit gets quite hot. I hope I can do something in the settings to reduce it.
Those 3 wire inlets into the box are not perfekt waterproof. small drops came inside.
Does anybody has a better Idea how to make the inlets waterproof, but still easy to disassemble.
The last thing is that the cheap china fuse can by far not withstand what is written on it (150A). Something in the inside melted and now it is not possible to trigger or close the fuse anymore. Is that issue know or did I just could have a faulty part? Anybody also using that part or another better one?
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Who wants to see what such a cheap efoil can do, see below.
I will improove the issues and then making a calculation, what it was overall. I assume it was more like 700€ but the battery is quite big.
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People used those in the early days 2019/20 but most cheap ones could not withstand more than 60A, no matter what they were rated.
Better use an antispark connector like xt90s or QS8S. If you want a fuse, midiOtto 150 - 200A is rated for 58V and is quite compact. Works well in my 2 boards.
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Here an update. I opened the fuse and the metal pins which are making the conection inside are held by cheap plastic which melted down. I excluded the fuse and did a second testrun:
(proper foiling skills ;))
Unfortunately the the ESC got to hot and is shutting down. I got a hint that maybe my prop does not have good efficiency. It is the prooven Volkers prop, but I printed with a bad printer and I deformed the prop maybe also a bit due to heat (I wanted to eliminate burrs at the edges and flamed it. The prop got very soft while that) and I also fixed an edge with UV-epoxy (I crashed the prop inside my door :D).
So I have bought a plastic flite prop and a flipsky aluminium folding prop and printed mounts for it:
I also bought a cheap china wifi amp/power meter and built it in the board to compare the new props (conection to smartphone works fine): https://a.aliexpress.com/_EzZ7fiA
The fuse I exchanged to 175A also from Ali: https://a.aliexpress.com/_EIVDPfu
So on the weekend I will test at least the flite prop. So let us see how it is going out.
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