Units and glossary
Units
Millimetres and inches — The mm / in control changes displayed lengths. Saved values, backend calculations, and exports remain in millimetres. Where a statistics overlay shows total lengths or areas, the display changes between metres and square metres or feet and square feet.
Percent (%) — A proportion of the related chord, height, width, or length, as named beside the control. The mm/in switch does not change percentages.
Degrees (°) — An angle. Used for values such as head angle, twist, sheet angle, wind angle, and cross-cut shear.
1:1 — Full size. One millimetre in the file represents one millimetre on the cloth or output device.
1:25, 1:10, and similar scales — Reduced print scales. At 1:25, 25 mm on the full-size panel becomes 1 mm on paper.
Boat and rig terms
LOA — length overall — The boat's overall length.
I — forestay top height — Vertical height of the forestay's upper point in the rig dimensions.
J — mast-to-forestay distance — Horizontal distance from the mast base to the forestay base.
P — mainsail luff length — Available mainsail luff length on the mast.
E — mainsail foot length — Available mainsail foot length along the boom.
Forestay offset — Distance from the bow to the forestay base.
Halyard pulley — The sail's upper attachment point relative to the mast top.
Sail geometry and shape
Tack — The lower forward corner, where luff and foot meet.
Clew — The lower aft corner, where foot and leech meet.
Head — The upper end of the sail. In Sail Design it can be a short edge with its own length and angle rather than a single point.
Luff — The forward edge from tack to head.
Leech — The aft edge from clew to head.
Foot — The lower edge from tack to clew.
Chord — The straight line between an edge's two end corners. Luff, leech, and foot chord values set those corner-to-corner distances.
Round — A signed offset of an edge from its straight chord. Positive Round produces an outward roach; negative Round produces a hollow edge.
Opening — A non-negative bow of an edge out of the original sail plane.
Position — The point along an edge chord where its Round and Opening reach their peak.
Camber or depth — The fullness of a horizontal sail section, shown as a percentage of that section's chord.
Draft — The position of maximum depth along a section chord, measured from the section's luff end.
Entry and exit — The controls that shape the forward and aft portions of a section profile around its deepest point.
Profile height — The position of an editable horizontal section up the sail, expressed as a percentage from foot towards head.
Fullness — The whole-sail multiplier that scales the depth of every section together. Saving applies the multiplier to the profile values and returns the control to 1.00×.
Twist — Rotation applied progressively to sections between the foot and head. Head twist sets the final amount; its distribution sets how the intermediate sections reach it.
Luff excess — Available rig-line length minus the sail's luff chord. A negative value means the luff chord is longer than the current tack-to-halyard line.
Tack pendant — Distance that the app raises the tack along the available rig line. Tack pendant max caps that distance; zero pins the tack at its anchor.
Mould — The three-dimensional surface built from the current outline and section profiles.
Cloth, layouts, and panels
Warp — Threads running along the length of a cloth roll. Exported panels can include a short warp-direction mark.
Fill — Threads running across the cloth roll, perpendicular to warp. Also called weft.
Bias — A direction diagonal to warp and fill.
Selvedge — The finished lengthwise edge of a cloth roll.
Roll width — The usable cross-roll width available for panels. It constrains maximum panel width and cloth-layout nesting.
Layout — The chosen pattern of seams and panels: Cross-cut, Tri-radial, Mitre, Biradial, or Traditional.
Panel — One piece of cloth cut as part of the sail.
Flat panel — The two-dimensional cut shape produced by flattening a panel from the mould.
Seam — A join between adjacent panels.
Seam overlay — The seam network drawn on the 3-D mould before flattening. It is a browser preview, not a generated panel set.
Broadseam — The shaped edge assigned at a Cross-cut join so a flat panel pair can reproduce the curved mould when joined.
Seam allowance — Extra cloth added on the owned side of a shared panel seam. Sail boundary edges do not receive panel seam allowance.
Declared straight edge — A panel edge labelled as straight by the current generator. The panel viewer paints it red; the label alone does not say that postprocessing changed the edge.
Panel display number — The short contiguous number shown on a flat panel and used by several exports. It is the convenient user reference for the current generated set.
Corner patch — One layer of reinforcement configured at the tack, clew, or head. A corner can have several nested patch layers.
Panel viewer — The full-screen canvas for inspecting generated flat panels. Its arrangement shows seam neighbours; it is not a nested cloth-roll cutting plan.
Nesting — Placing flat panels on one or more bounded sheets or cloth strips to create a shared output layout.
Diagnostics and exports
K — Gaussian curvature — A signed surface-curvature field. Negative values are saddle-like, values around zero are locally developable or flat, and positive values are cap-like.
H — mean curvature — A signed measure of the mould's mean bend relative to its surface normal.
Saddle — The categorical mould-fairness view that labels regions saddle, fair, or masked. It is separate from the continuous K heatmap.
TWS — true wind speed — Wind-speed input for the wind-dependent Heatmaps fields, displayed in knots.
AWA — apparent wind angle — Wind-angle input for the wind-dependent Heatmaps fields.
Pressure — The Heatmaps field showing modelled pressure on the windward face in pascals.
Stretch energy — The Heatmaps field showing modelled elastic energy density in joules per square metre.
Offset table — A list of measured offsets used to plot panel edges by hand. The accompanying drawing is schematic rather than a cutting template.
Calibration square — A printed square with a stated real-world size, used to check that a full-size or reduced-scale PDF was printed at the intended scale.
Registration cross — A repeated alignment mark used to join neighbouring pages of a tiled print.