I got this boat when I was a kid in the 80's. Although the boat was not certified for sea water I did run it in the sea as our cottage was by the sea. The Sea of Bothnia is not as salty as ocean water but there are some corrosion issues, mainly with the screws and motor.
The first thing to repair was the propeller, which was completely broken with one missing blade. I attempted to 3D print a new prop. The result was terrible as the overhang is too much. I did not expect it to work but no hurt in trying.
I made a second print with a support structure. It is a lot of work to grind off the support as I used PLA, which is hard to sand or file. Then there was a lot of work making the print smooth and solid. I did several steps of adding cyanoacrylate-talcum mixture and sanding. It was hard work. Printing it using ABS would probably have been easier.
As a last step I painted the prop black and hot-glued it to the axle.
As I got a working propeller I could start fixing other issues. Following pictures are from the original condition while I was disassembling it.
Next thing to overhoul was the motor, which was badly corroded but functional. I just cleaned it, gave it some zinc paint and greasing.
Then I moved on to repair broken plastic parts. Many of the screw sites were cracked or completely broken. I 3D printed new parts in ABS and glued them in place with epoxy. Smaller cracks I only filled with epoxy. I replaced all screws with A4 stainless steel M3 machine screws suitable for marine applications.
Some paintjob was needed for chrome parts.
The power switch was also completely broken. I replaced it with a waterproof switch, which also needed modification of the mounting by a 3D printed ABS part.
For the battery compartment I made a modification that better prevents water to reach the batteries. There is always some leakage and bilge water. I blocked some slots to prevent bilge water to flow under the batteries.
Final assembly with new battery wires.
