See it in action
EDIT from the future DISCLAIMER: This project took at least 2 months of shorting electronics to get working in water. Even if you are broke and have all the time in the world it wasn't fun. I tried using these techniques to make a new quad the next year and it took another 2 months of failure to get one working and one day it hit the water for the last time. I'm not updating this build log as these techniques are just not reliable.

This build list is a collection of random stuff I had laying around and I got it all very cheap through sales. I fully expect this ship to return to davy jones someday. v1 was dismantled not lost at sea, it had 1804 motors to be as light as possible but wasn't a blast to fly.

Floatation

The floatation foam is motor packaging, this heavier v2 needed a lot more to make it float level and stable in waves so it ended up looking like an iceberg. The foam is hot glued or I used high strength double stick tape to keep adding pieces on while testing buoyancy in the sink.

Waterproofing

The last picture shows what you can use. Conformal coat (I used urethane) and liquid electrical tape are needed. CorrosionX for all connections and plugs. Drydrone is just there so I can say don't use it, it's basically garbage. And water-based polyurethane is good for escs.

Use thick applications of conformal coat but avoid buttons: receiver, esc, pdb, camera board
Liquid electrical tape but don't cover LEDs: vtx, camera case with plug in

We aren't worried about overheating since this stuff is water cooled, way more efficient than air.

Frame choice

You might be wondering why I used such a weirdly outdated frame. It crashes into water not trees so plastic is fine. The arms curve up so the motors are pushed out of the water further. The plastic is a better surface to glue/stick foam to than carbon unless you roughen the carbon first. For the frame size (260mm) it weighs only 124g and you want a larger platform for stability in the water. The further away those outriggers are the better. And most importantly because I have 5 of this frame from when hobbyking was selling frames for $1.

Final thoughts

Radio waves do not propagate through water at our frequencies! if your antenna goes underwater you lose signal, video feed especially. One receiver antenna is pointed down so if it's upside down in water I still have a signal to arm and roll it back over.

Batteries can get wet, watch OG Peter Sripol toss one in a tub of water (https://youtu.be/s4z8QMgTEA4?t=909)
But, water gets stuck under the heat shrink so I only use a couple unwrapped packs for this

I've flown in wind and it doesn't handle differently from a build without a bunch of foam hanging off it.

Any questions or things I missed put it down below