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Hull Lab and boat files
Beta release
Hull Lab is a beta feature under active development. The steps here work in the current release, but the workspace and its controls may change.
Hull Lab is a separate MakeSail workspace where you turn a boat's lines drawings into a hull your sail designs can use.
A boat file is the portable JSON file Hull Lab produces and the sail designer reads. It holds the boat's length, rig measurements, and traced hull lines, and can optionally carry a scan image. It is a different file from a saved sail design, which holds a complete sail. One boat file can back many sail designs, and each design that used a boat file carries its own copy of it inside the saved design.
Open Hull Lab
Hull Lab lives at /hull-lab on the MakeSail site. It needs no account or sign-in.
From the sail designer, the quickest route is File > New, then the link Your boat not listed? Build it from its drawings at the bottom of Step 1. You can also open https://makesail.nl/hull-lab directly.
The top bar reads MakeSail Hull Lab with a Beta badge. Alongside the File and View menus it shows the view chips Profile, Section, and Plan, and a 3D / Trace switch at the right.
Start from a built-in hull or a new file
Hull Lab opens with a built-in boat selected. The File menu gives three starting points:
- File > Open built-in ▸ lists the boats MakeSail already knows. Entries marked (rig only) have no traced hull yet; picking one opens a blank hull with that boat's rig numbers.
- File > New (Cmd/Ctrl+N) starts a blank hull from the selected built-in boat's rig numbers.
- File > Open… (Cmd/Ctrl+O) opens an existing boat file.
There is no unsaved-changes prompt in Hull Lab. File > New, File > Open…, and picking a built-in all replace the current work immediately, so save anything you want to keep first.
Load and calibrate a scan underlay
The tracing canvas uses its own scan image, loaded inside Trace mode. Switch to Trace with the top-right switch, then load an image in the Image section of the side panel — a photo or scan of the boat's lines drawing. You can also trace on the blank canvas without an image.
Before the draw tools work, register the image to the hull. Select the view you are tracing — Profile, Section, or Plan — then choose Calibrate from LOA and click the bow tip, then the stern tip. This sets the scale from the boat's length.
- In the Profile view, two further clicks on the waterline level the view and set the waterline height.
- In the Section view, Calibrate sections asks first for two points on the centreline and then a span click across the hull; enter the half-beam distance in millimetres to set that view's scale.
The draw tools stay disabled until the loaded image is calibrated. Loading a new image discards the old registration, so you calibrate again.
The 3-D editor's side panel has a separate Underlay section. It places a scan on the profile, section, or plan plane of the 3-D preview and is the image the boat file can optionally carry as its saved preview — see Save and reopen a boat file.
Trace the hull
The hull tab lists the elements you can trace, each in the view where it belongs: gunwale, keel line, keel appendage, rudder, cabin, cockpit coamings and floor, transom, hull sections, companionway, portholes, winches, and deck rails. Some elements only unlock once their source lines exist — for example the transom needs the keel and gunwale, and portholes need the cabin.
The trace toolbar holds four tools:
- Polyline places straight-segment points.
- Spline places curve control points.
- Select drags points, adds a vertex when you click a segment, and deletes a point on right-click.
- Rotate levels a skewed profile trace by dragging it about the forestay base.
Double-click or press Esc to finish a line. Undo and redo work with Cmd/Ctrl+Z and Cmd/Ctrl+Shift+Z.
The rig tab holds the rig measurements and suggested values. Capture rig points by choosing one from the dropdown and clicking the profile view, then edit the I, J, P, E and other rig numbers directly; suggested values computed from your clicks appear next to each field.
Inspect the result
Switch back to 3D to see the traced lines lifted into the hull model. Use the Profile, Section, and Plan chips to snap the camera, and the View menu to toggle the anchor markers and grid.
The Hull file section of the side panel lets you rename the boat and adjust its length and main rig numbers. The forestay offset is in the tracer's rig tab. New hulls use the traced bow as the sheer datum; opening and saving an existing hull preserves its stored sheer height.
The Representation preview row chooses what the sail designer renders when this boat file is opened there: Underlay (the saved scan) or Traced lines. The choice is stored in the boat file. With no trace elements yet, the 3-D view shows stored hull lines, if any.
Save and reopen a boat file
File > Save (Cmd/Ctrl+S) writes the boat file. The first save asks for a destination and suggests a name ending in .hull.json; later plain Saves overwrite that file. File > Save As always asks for a new location. In browsers without the native file picker, Save downloads the file. Save is briefly disabled while the trace finishes loading.
Underlay images are opt-in: in Underlay, tick include underlay images (opt-in, downsampled) below the file picker to store the 3-D underlay in the file. The image is downsampled before it is written, and a file set to render the Underlay representation cannot save without a calibrated, included image.
File > Open… reopens a boat file — Hull Lab accepts .hull.json, .boat.json, and any .json boat file — and restores its traced elements, rig numbers, and included underlay. Plain Save after an open overwrites the same file where the browser's file picker supports it.
Start a sail design from a boat file
In the sail designer, open File > New. In Step 1, choose + Local boat file… from the boat list, or the Open local boat file… button, and pick a boat file. The summary shows its I, J, P, E, and length, and Local hull: <name>.
Select Next →, then choose a sail type. The design opens with the boat file's rig numbers, and the hull lines appear in the 3-D preview when Show boat is on.
The sail designer does not edit the hull. To change the hull itself, reopen the boat file in Hull Lab, edit it there, and start a new design from the updated file.
Recover the boat file from a saved design
A saved sail design that started from a boat file carries that boat file inside it. To get the standalone boat file back, open the design and choose File > Extract Boat…. The browser downloads <boat-name>.hull.json, the same format Hull Lab saves and reopens. The menu item is disabled when the current design has no local boat.