How to Seal and Waterproof a 3D Printed RC Boat Hull

Every FDM print leaks a little. Water finds its way through the tiny gaps between layers, especially at seams and screw holes. A printed hull runs dry when you seal it before the electronics go in, not after the first wet ESC.

1. Glue the sections

Join the hull sections with CA or epoxy. Clamp them square and let them cure fully. A seam that isn't fully glued will leak no matter what you put over it.

2. Fill and sand the seams

Fill the seam lines with filler, let it cure and sand smooth. This is also what makes the paint look like one piece instead of a stack of sections.

3. Seal the inside

Brush fiberglass resin inside the hull, working it into every seam, corner and around the transom. This is the coat that keeps the water out. Let it cure fully before the next step.

4. Finish the outside

Prime, sand and paint the outside. Paint alone is not a seal, but primer and paint over a sealed hull protect the print and finish the look.

5. Seal the openings

Anything that goes through the hull needs its own seal: the outboard mounting bolts, the water-cooling lines, the rudder or shaft if your boat has one, and the hatch. Seal through-hull bolts and fittings, and tape the hatch before each run.

6. Water test it before the electronics

Once the inside and outside are both sealed, put the hull in the water before any electronics go in. Then dry it off, open it and look for water. Fix any leak now, while there is nothing inside to ruin.

Before every run

• Hatch taped or sealed
• Water-cooling lines connected
• A paper towel in the hull: if it's wet after the first run, find the leak before the next one

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