The Sturmvogel had spent several summers sailing its owner's garden pond. UV light and moisture had done what they always do to cheap injection-moulded plastic: bleached it from cream to chalk white, made it brittle, and left the sails looking like they'd been salvaged from a shipwreck. The mast had broken and been repaired at least twice with epoxy putty. A friend brought it to us not to replace it, but to save it.
What We Were Working With
The boat is a Günther 1810 Segelboot "Sturmvogel", a sailing model with a solid hull, wooden deck, and a full plastic superstructure. The superstructure covered everything: the main cabin, all the deck fittings, the mast base, the sail attachment hardware, and dozens of small cleats and brackets.
Most of the plastic had gone so brittle that pressing it with a fingernail left marks. The original sails were stained and torn. The boom and gaff (the horizontal wooden beams that hold the sails) had warped into a curve and couldn't be straightened. The deck, however, was solid. The wooden hull was in good shape. The mast itself, a simple wooden dowel, had some finish left worth saving.
We inventoried what could stay and what needed rebuilding. Kept: the hull, the deck (sanded and refinished), and the main mast after sanding. Replaced: every plastic part, both sails, the bent wooden beams, and most of the rigging hardware.
Designing the Replacement Parts
The largest piece was the main cabin body: an elongated form with a raised hatch, mast socket, and several small bracket attachment points along its sides. We started it in CAD for dimensional accuracy, printed a thin full-scale prototype to verify its fit on the deck, then moved into Blender for the surface detailing. Blender was faster for purely aesthetic shapes where precision wasn't needed, and the freeform modelling tools handled the curved transitions better than constrained CAD geometry would have.
The smaller parts (cleats, sail slides, mast fittings, and the deadeyes for the rigging) were straightforward CAD work. None of them were geometrically complex, but print orientation mattered: each part needed to sit on the build plate in a position that maximised layer adhesion along its load axis, since these parts would live outdoors on a pond.
One fitting (the connector between the mast and the boom) went through three iterations before the geometry worked cleanly. The original mechanism was buried under old epoxy repairs and we couldn't examine it. No close-up reference images existed for this model either. We improvised a hook-and-seat design that held the boom at the right angle and was straightforward to print without support.
For the sails, we removed the original set, laid both panels flat, and measured them carefully. The mainsail is 450mm tall and 190mm wide; the foresail is 330mm tall and 155mm wide. We modelled both shapes in CAD including the hem allowances, hole positions, and grommet spacing, then printed the outlines as flat cutting templates.
Printing in ASA for the First Time
We chose ASA for all the plastic parts. The Sturmvogel was going back into a garden pond, and PLA would degrade in direct sun within a season. PETG would have been acceptable, but ASA offers better UV resistance and a stiffer feel that matched the original parts more closely. We had not used ASA before this project.
The first print of the cabin body made the problem immediately clear.
The part was too long to fit squarely on the build plate, so we rotated it 45 degrees diagonally and shortened the tail by a few millimetres. With printing tape, the corners lifted before the print reached half height. We switched to 3DLac on the next attempt: same result. Reducing print speed significantly on the third attempt bought a little more time before the edges curled up. The part was also too large for a brim to be practical. ASA shrinks more aggressively during cooling than PLA or PETG, and the long continuous perimeters gave the warping forces nowhere to dissipate.
The Anti-Warp Geometry Fix
Bed adhesives can help a lot, but they don't address the root cause. What was happening: the long straight perimeter lines at the bottom of the part were shrinking as they cooled, pulling the edges upward. The solution was to interrupt those lines.
We added a grid of broad parallel slits to the underside of the cabin: slots cut into the base geometry, perpendicular to the longest dimension of the part. The slits don't go deep enough to affect the exterior surface finish, but they break every long perimeter line into a series of short segments. Short segments shrink independently; they don't accumulate into a force large enough to lift the part.
The next print came off the bed flat. No adhesives, no enclosure. Just the geometry change.
Sails, Spars, and Rigging
The original sail fabric was beyond reuse: stained, torn, and the wrong weight for the fittings. We cut the new sails from a lightweight tent fabric: translucent, dimensionally stable, and light enough to catch a gentle pond breeze. The CAD templates gave us accurate cut lines and grommet positions, and after sewing the hems and setting brass grommets, the two sails matched the original dimensions closely.
The wooden mast was worth keeping: sound, straight, and already fitted with the right diameter for the socket. We sanded it back to bare wood and left it as-is. The bent gaffs and booms were not salvageable, so we replaced them with wooden dowels in the same diameter, fitted with the printed ASA connectors.
Rigging a model sailboat without any sailing knowledge is, it turns out, a specific kind of challenge. We studied enough reference photos to understand the basic lead of the lines and bound the ropes in a way that looked plausible and would hold the sails at the right angles. Our friend, who does know how a sailboat works, will redo the ropework properly before the boat goes back on the water. We handed it over as a functional placeholder.
One fitting we hadn't planned for: a small plastic eye on the bow deck had broken off at some point and been filled flush with epoxy. We couldn't cleanly remove the old adhesive without damaging the deck, so instead we drove a metal eye screw directly into the exposed plastic stub beneath the epoxy. It holds better than the original did.
The Finished Boat
All printed parts were in filament colour: off-white for the cabin and structural parts, red for the accent hardware. No post-print painting. The red parts came out sharp enough that painting would have been a step backwards.
What This Project Taught Us
ASA warps more aggressively than any other common FDM material we have used. The fix: break the long bottom perimeters into short segments and the shrinkage forces have nothing to accumulate into. We've since used the same approach on other large flat ASA parts.
Print orientation for outdoor or load-bearing parts deserves more attention than it usually gets. Printing a part flat because it looks better is often the wrong call. We printed every fitting on this boat in the orientation that put the layer boundaries perpendicular to the primary load direction. The small parts, at least, should outlast the original plastic by a considerable margin.
The cabin workflow (CAD for dimensions, Blender for surfaces) is one we've settled into for parts that need to be both precise and visually convincing. Starting in CAD and finishing in Blender is faster than doing everything in one tool, and the results are cleaner than trying to extract accurate measurements from a purely organic mesh.