Set units to millimetres

Type UNITS ↵. Set Type = Decimal, Insertion scale = Millimeters. Click OK. Everything you draw is now in mm matching the model scale.

Create the layer set

Type LAYER ↵ and create these:

UNDERLAY     colour 8  (grey)   — the PDF underlay
STATIONS     colour 3  (green)  — vertical station construction lines
KEEL         colour 1  (red)    — baseline / keel
DECKLINES    colour 4  (cyan)   — deck heights from sheer plan
STN_b … STN_12, FWD_PP          — one layer per traced section
BULB         colour 6  (magenta)
SHAFT_BOSS   colour 2  (yellow)

Attach the Body Plan PDF as an underlay

Type PDFATTACH ↵ → choose SS_Andrea_Doria_Body_Plan_1-72.pdf → insertion point 0,0, scale 1, rotation 0. Put it on the UNDERLAY layer.

Calibrate the underlay to true scale

The PDF imports at an arbitrary size. Fix it:

1. Type DIST ↵. Snap from the centreline to the widest point of station 6 (the outermost full section). Read the distance D.
2. Scale factor = 190.28 / D.
3. Select the underlay → SCALE ↵ → base point 0,0 → type the scale factor ↵.
4. Re-measure: the half-beam must now read 190.28 mm. The full beam = 380.56 mm.

Draw the centreline and keel

On KEEL, draw a vertical line at X=0 (the section centreline) and a horizontal line at Y=0 (the keel baseline). All sections are measured from these.

Trace one half-section with SPLINE

Set the current layer to the station (e.g. STN_6). Type SPLINE ↵. Click points along the hull curve from the keel up to the deck edge, following the underlay. Use 10–20 points — enough to capture the bilge curve smoothly. Press ↵ to finish.

Mirror to the full section

Body plans show one half. Select the spline → MIRROR ↵ → mirror line along the centreline (X=0) → keep both. You now have port + starboard.

Join into one closed profile

Select both halves → JOIN ↵ (or PEDIT → Join). Then PEDIT → Close to seal the loop at the keel. A closed profile is what the loft needs.

Repeat for every station

Work through STN_b, STN_a, STN_0, STN_1 … STN_12, FWD_PP. For the aft frames (b, a, 0) use the Stern Body Plan underlay; for stations 10–FWD PP use the Bow Body Plan underlay. Each goes on its own layer.

Trace the bulb and shaft boss separately

On BULB, trace the teardrop profile at the bow centreline. On SHAFT_BOSS, trace the bossing and strut from the stern body plan. Keep these off the station layers — they’re modelled separately.

Export each station layer to DXF

Isolate one station layer (freeze the others), type SAVEAS → AutoCAD R12/LT2 DXF (most compatible with FreeCAD). Name it after the station. Repeat per station. Position them in FreeCAD using the X-table.

Move each section to its X-position

The sections are drawn in the XY plane but represent the YZ (transverse) plane. Rotate each 90° about the X axis so it stands up, then move it along the length axis to its station X (from the table in the Overview). Use 3DROTATE and MOVE.

Export the whole model as one DXF

SAVEAS → AutoCAD 2013 DXF. All stations export together with their layer names, ready for a single FreeCAD import.

Set the document to mm

File ▸ Document Properties ▸ Display units = mm.

Import the body-plan PDF

File ▸ Import ▸ choose the PDF ▸ import as a single object. It comes in as vector paths.

Scale to true size

Select the imported group. In the toolbar W/H boxes (units = mm), set the width to the sheet’s physical width 583.1 mm with the lock-ratio padlock on. The drawing is now at model scale.

Lock the PDF, trace on a new layer

Layer ▸ Add Layer (one per station). Lock the PDF layer. Use the Bézier/Pen tool (B) to trace each half-section, keeping nodes few and smooth. Press Enter to finish each path.

Smooth and mirror

Select the path ▸ node tool (N) ▸ select all nodes ▸ “Make selected nodes smooth”. Then Object ▸ Transform ▸ Flip Horizontal to mirror, and Path ▸ Union to merge halves into one closed path.

Save as Plain SVG

File ▸ Save As ▸ Plain SVG. FreeCAD imports this via File ▸ Import.

Confirm units and size

The STL should be in mm. A hull section is ~274 mm long. If your slicer shows it 25.4× too big or small, it read inches — re-export from FreeCAD with mm.

Run a mesh repair pass

Both Bambu Studio and OrcaSlicer auto-detect non-manifold edges on import and offer a one-click repair. Accept it. (The provided sections are already watertight, but it’s a good habit.)

Plan the split vs your bed

Bambu A1/P1/X1 bed = 256 × 256 mm. The ~274 mm sections are slightly too long to lie flat — they’re meant to print standing on a cut face (vertical), which fits easily. If you prefer flat printing, re-split into shorter pieces (~240 mm).

Import the section STL

Drag the STL onto the plate, or File ▸ Import ▸ Import 3MF/STL. Accept the auto-repair prompt if shown.

Orient on a cut face

Right-click the model ▸ Place on face ▸ click one of the flat transverse cut faces. The hull section now stands vertically — clean hull sides, flat base, fits the bed.

Make it hollow (if the STL is solid)

Set walls + low infill (next column) — that hollows it. Or use the dedicated tool: Bambu/Orca both have a “Hollow” option under the right-click ▸ modifications in some versions; the wall+infill method is more predictable for a hull.

Slice and inspect

Click Slice plate. Use the layer preview slider to check walls are continuous and supports only sit under true overhangs.

Export

Bambu: send to printer over LAN/cloud, or export the .3mf / .gcode to SD. Orca: export G-code for your printer profile.

Dry-fit in order

Lay sections 01→10 in sequence and check the cut faces meet. The matching profiles should line up since they came from the same loft.

Pin and glue

Insert short dowels/filament pins into matching holes (if you added them in CAD), then bond cut faces with cyanoacrylate (CA) or epoxy. Epoxy gives working time to align.

Fill and fair the seams

Skim seams with modelling filler, sand fair (220→400 grit), prime, and check the hull line is continuous across joints before painting.