This guide walks you through the first workflow in StowMind: getting your ship into the software, creating the StowMind hull object, and running the first hydrostatic calculation. The whole process typically takes 10 to 30 minutes for an existing geometry file.
StowMind supports three hydrostatic methods: slice-based (requires a watertight solid), frame-based (works on solids, shells and compounds), and yard-data-based (works from tabulated CSV data, no geometry needed). This page covers the geometry import workflow first, then the yard-data method.
Tip: If you have never used StowMind before, start with one of the four included example vessels (Series 60, Wigley). This lets you see the full workflow before importing your own geometry.
Not all hull geometry formats are equal. GF spant files are the most reliable for StowMind because they carry explicit station positions and point counts. DXF files work well when they come from a clean CAD export, but may need cleanup for older or hand-drawn drawings. The table below shows what to expect.
| Format | Best for | Reliability |
|---|---|---|
| GF / GF1 | Hull geometry from the GF editor or a shipyard dataset | ★★★★★ — explicit stations, no parsing ambiguity |
| DXF | Station drawings exported from AutoCAD or similar | ★★★☆☆ — works well with clean exports, needs cleanup for older drawings |
| IGES / STEP | Full 3D hull solids from a CAD system | ★★★★☆ — reliable if the solid is watertight |
| STL | Mesh exports for quick testing or when only a mesh exists | ★★★☆☆ — converted to a solid automatically, small gaps may need tolerance adjustment |
| Yard CSV tables | Hydrostatics and KN curves from a stability booklet | ★★★★★ — no geometry needed, direct reference data |
Rule of thumb: If you have a choice, use GF. If you only have DXF, check the drawing first against the pre-import checklist below. IGES/STEP is the best option for full 3D models. If no geometry exists but yard data does, use the yard-data method described further down.
STL and IGES/STEP with defects: STL meshes and STEP/IGES solids occasionally arrive with flipped faces or holes. StowMind attempts to harmonise normals and close small gaps automatically during conversion. If the conversion still fails, do not discard the file — repair it manually in a scratch FreeCAD document first:
.FCStd and import that file, or select the solid and use Use selected object.This manual repair route is often faster than trying to fix the original export in the CAD system, especially for STL meshes from third-party sources.
DXF drawings from different CAD systems vary widely. Before importing a DXF file, check these five points. If one of them fails, the drawing will need a small cleanup in your CAD software before StowMind can build a reliable hull.
What StowMind does automatically: Unit detection (mm vs. metres), station orientation correction, duplicate station removal, and small-gap filtering. What needs manual cleanup: splines instead of polylines, missing elevations, stations that stop below deck, and stations with two points.
The following steps apply to all geometry formats. The only difference is how the geometry arrives in the FreeCAD document.
Start FreeCAD 1.1 and create a new document. Activate the StowMind workbench from the workbench selector.
Import your hull file via the StowMind import tool, or load an example vessel, or build sections directly in FreeCAD. If you are importing a DXF file, run through the DXF Pre-Import Checklist above first. GF and IGES/STEP files usually import without changes.
StowMind converts meshes to watertight solids, mirrors half-spants to full sections, and lofts them into a complete hull. This step is automatic for most formats. If the conversion reports that the hull is not fully closed, the cause is usually a station that does not reach the deck line or a station with too few points. The console log names the affected station. For STL or IGES/STEP files with flipped faces or holes, see the manual repair workflow in the format comparison above.
Use the StowMind tool palette to create a StowMind hull object. This object is the anchor for all subsequent calculations and shares the same coordinate system as the rest of the document.
Run the hydrostatic calculation to verify the hull is watertight and the displacement is plausible. Results appear as FreeCAD spreadsheets and plots, including frames, cross curves, and pantocarenes.
Define tanks and weights, calculate the load condition, and proceed to stability (SOLAS / IS Code 2008), lashing (IMO CSS Code Annex 13), or crane and rigging analysis (DNV-ST-N001).
Sanity check after Step 5: The calculated displacement should be within a few percent of the known displacement of the vessel. If it is off by an order of magnitude, the hull solid is likely not closed or the scale is wrong. StowMind will flag this in the hydrostatic report.
If you have hydrostatic tables and KN curves (pantocarenes) from a shipyard stability booklet, you can use them directly in StowMind – without building a hull solid first. This is useful in two situations: when no 3D geometry exists at all, and as an independent reference against which the slice-based and frame-based methods can be validated.
Two CSV files are needed:
Any spreadsheet program can produce these files. The only requirement is a clean CSV export with a header row – StowMind reads the column layout from the header.
Hydrostatic_Yard.PantocarenesCurves_Yard.Alternative naming: If no other yard data exists in the document, the two spreadsheets can be placed in the document root without the _Yard suffix – as Hydrostatic and PantocarenesCurves. StowMind uses them directly in that case.
Select a similar vessel from the included examples (Series 60, Wigley) or from an existing model, then apply affine scaling to stretch it to the target dimensions (L, B, D). The scaled hull acts only as a geometric placeholder for visualisation and for the modules that need a reference body. The hydrostatic results come from the yard tables, not from the placeholder geometry.
Why this method matters: It is the only approach that works without a watertight solid and without any 3D geometry at all. It is also the reference against which the slice-based and frame-based methods can be cross-checked – if the calculated results deviate from the yard tables, the input geometry needs attention. A deviation report per parameter and per draft is available in the hydrostatic export.
| Method | Requires | Typical use |
|---|---|---|
| 1. Slice-based | Watertight solid | Fast hydrostatics from 3D models; also feeds Capytaine |
| 2. Frame-based | Solid, shell or compound | Works when the loft produced only a shell or compound; slower but robust |
| 3. Yard data | Two CSV files | No geometry available, or validation reference for Methods 1 and 2 |
StowMind imports GF spant files, DXF, STL, IGES/STEP, and native FreeCAD files. GF files are the most reliable because they carry explicit station positions and point counts. DXF works well with clean CAD exports but may need cleanup for older drawings. IGES/STEP is the best option for full 3D hull solids.
If you have a choice, use GF spant files. They are the most reliable format for StowMind because station positions and point counts are stored explicitly. DXF is the next best option when it comes from a clean modern CAD export. IGES/STEP is recommended for full 3D hull models. STL is suitable for quick testing or when only a mesh is available.
No. StowMind includes four example vessels (Series 60, Wigley) for immediate testing. You can also start with a half-spant model or a simple parametric hull and refine it later. If no geometry exists at all, yard hydrostatics and KN curves from CSV files can be used as a third method.
Check five points: (1) stations are POLYLINE or LWPOLYLINE entities, not splines; (2) each station has an elevation set in the polyline Z position; (3) stations are ordered keel to deck; (4) stations extend to deck height; (5) no station has fewer than three points. If any of these fails, the drawing needs a small cleanup in your CAD software before importing.
StowMind discards stations that are too small to form a reliable loft – for example, a station at the very tip of the bow with only two points. If the bow or stern has stations like this, the hull will be shortened by the distance to the last usable station, typically a few hundred millimetres. To keep the full length, extend the tip stations to at least three points in your CAD software before importing.
Some stations in the drawing may not reach the deck line. When a station ends below the deck, the loft connects it to the next full-height station with a slope, which appears as a dent. Check the drawing in your CAD software: every station should extend to the deck line, or the drawing should be re-exported from the original source.
Not always. Clean DXF exports from modern CAD systems (AutoCAD 2000 or later, Rhino, ShipConstructor) usually import without changes. Older drawings, hand-drawn sections, or exports from non-marine CAD tools may need a small cleanup: converting splines to polylines, setting the polyline elevation, or extending stations to deck height. The pre-import checklist above lists the five points to check.
StowMind includes a mesh-to-solid conversion step that closes small gaps and creates a watertight solid. For larger defects, the hydrostatic calculation will report an implausible displacement, which is the signal to check the input geometry. The console log names the affected station.
StowMind tries to harmonise normals and close small gaps during conversion. If the result is still unusable, repair the file manually in a scratch FreeCAD document: import the file there, switch to the Mesh workbench to harmonise normals, fill holes, and remove duplicate points, then use Part → Convert to solid in the Part workbench to produce a watertight solid. Save the result as .FCStd and import it into StowMind, or select the solid and choose Use selected object. This route bypasses the importer's conversion step entirely and is often the quickest fix for defective STL or STEP files.
Yes. StowMind supports a third hydrostatic method that works entirely from tabulated yard data. The hydrostatic values and KN curves are stored as two CSV files, imported into FreeCAD as spreadsheets, and placed under the Yard group as Hydrostatic_Yard and PantocarenesCurves_Yard. If no other yard data exists, the files can be placed in the document root without the _Yard suffix. The vessel is represented by a similar example hull that is stretched to the target dimensions using affine scaling; the hydrostatic results come from the yard tables, not from the placeholder geometry.
Two CSV files are needed: one with hydrostatic values per draft (displacement, LCB, KB, GM and similar), and one with KN values or cross curves per heel angle and displacement. Both are imported into FreeCAD via the standard spreadsheet import function and stored under the Yard group as Hydrostatic_Yard and PantocarenesCurves_Yard. Without the _Yard suffix, the files are read directly from the document root.
For an existing GF spant file or a clean DXF export, the import and first hydrostatic run typically take 10 to 30 minutes, depending on the model complexity and the number of frames. For the yard-data method, setup time depends only on preparing the two CSV files.
Yes, for some workflows. Crane and rigging calculations can start from a parametric crane object and a load condition spreadsheet, without a complete hull. Stability and lashing calculations normally require a hull solid, but the yard-hydrostatics method allows stability work from tabulated data alone.
The StowMind YouTube channel includes walkthroughs for each import format – installation, hull import from GF and DXF, example vessels, the first hydrostatic run, and the yard-data workflow.