Fin Designer
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OUTLINE Drag points and arms · double-click to add · press and hold a point to delete · scroll to zoom · arrows move selection · Alt-click: corner/smooth Pencil: tap a point for actions · press and hold to delete · finger: pan or pinch
left-drag: orbit · right-drag: pan · scroll: zoom
Foil Cross-Section
Thickness Profile
scroll zoom · drag blank space to pan · arrows move selection (Shift: coarse, Alt: fine) · dbl-click add · right-click remove · alt-click: corner/smooth · shift-drag arm: snap axis
Design settings
Fin Sets
One .finset file holds every size and role in a Single, Twin, Thruster, Quad or 5 Fin family. Each fin pair uses one saved design.
Create a set to start.
Ghost Overlays 0
No overlays. Ghost a saved fin from the presets list, or load one below.
Live Stats
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Base mm
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Depth mm
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Rake mm
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Area cm²
Parameters
mm
mm
mm
mm
mm
Foil Section
% chord
The crest (dashed amber line on the outline) is the foil's thickest line. The front bevel follows the outline from the LE base round to its tip point; the rear bevel follows the TE. Drag its squares (base / tip ends) and circles (shape) to reshape it. Crest at sets where the auto crest sits on the lower fin.
Most surf fins use symmetric NACA 00xx sections around 9–12% thickness with max thickness ~30% back from the leading edge (Max thickness above sets this) — the presets above follow that convention.
mm
The outside curve is picked up and shifted away from the outline by this much, unchanged in shape — not reshaped or blended — so it reads exactly this value at the true LE/TE, and adds the same amount everywhere else too, including at Max Thickness (0 = pinch to a knife edge, matches the outline rails exactly). On symmetric foils it's split evenly between both faces; on Flat/asymmetric foils the flat inside face stays flush and the full amount goes to the outside face.
Special-case single concave: a shallow dish scooped off the flat inside face. Off by default and independent of the foil preset — leave it off for normal fins. The dish stays clear of the leading/trailing edges and rails and fades out up the span, so it never reaches the tip.
Base Attachment
System
Variant
Reference Library ▸
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Photo Reference

Drop or click
to load reference

The photo and its calibration are working aids only: they are not saved in .fin files or in the browser recovery copy, so load the photo again after reloading or opening another design. A traced outline you apply becomes part of the design and is saved with it.
Curves
Leading edge
Trailing edge
Thickness rail
Saving & Recovery
No changes yet.
The reference photo and its calibration are not stored in a .fin file or in the browser recovery copy. After reloading or opening another design, load the photo again and recalibrate.
Save Folder & Groups
Groups — saved into the .fin