I converted an old RC Helicopter into an RC Boat.
It isn't great but I'm proud of how it turned out, it was a fun project to work on. I plan on adding some details to the top part as a cleaner way to store the main control board, but I haven't figure out a good way to do that while still maximising printability (If you can think of something good remix the top, I'd like to see what you can come up with!).
I haven't tried it yet, but it is probably possible to get the electornics from an eachine e11 or other micro sized quad instead of the helicopter to have better control over the boat's movement.
The HeliElectronicsTestBed.stl is what I made and used to hold the motors in place while I tested their controls after taking apart the helicopter. It is not necessary for the boat itself, but if you want to make your own RC Helicopter conversion I would recommend using it to keep the motors from spinning all over the place.
Q: Is it water-proof?
A: Probably not, but I've submerged it completely a few times and it still works fine.
Q: Does it work well?
A: No, It is very difficult to control and usually sinks.
I used 0.25mm layer height for a faster print, but anything works
I printed the Hull in the original orientation of the .stl file, but I printed the top flipped 180 degrees to avoid supports.