Edge shape and twist
Change the sail outline and its three-dimensional opening from the right-hand Shape card, then use Sail Shape when you need exact values for every edge at once.
Find the two editing surfaces
| Surface | Open it from | Best for |
|---|---|---|
| Preview card | Select Preview in the right-hand Shape card | Watching a quick edge, sheet-angle, twist, or fullness change on the sail |
| Sail Shape dialog | Design > Sail Shape | Entering exact cord, head, edge, twist, profile, and mould values in one dialog |
The two surfaces edit the same settings. One deliberate exception is foot opening: Preview does not show a Foot opening slider. Select Profile Edit > foot and use Depth, or enter Foot > Opening (%) in the Sail Shape dialog.
Preview controls on the preloaded Albin Vega 27 gennaker example. File > New supplies different starting values for other boats and sail types.
- Live edge and surface result
- Mould and view controls
- Round, opening, and position
- Head twist and distribution
Understand Round, Opening, and Position
Edge controls shape the boundary; twist rotates horizontal sections progressively toward the head.
| Control | Meaning in the current UI |
|---|---|
| Round (%, signed) | Cloth offset from the straight chord. Positive produces an outward roach; negative produces a hollow edge. |
| Opening (%) | Non-negative leeward bow out of the original sail plane. |
| Position (%) | Location along the chord where the combined round and opening reach their peak. |
Round and Opening share one Position. Moving either shape component therefore does not introduce a second, independent twist along the edge.
Current edge ranges
| Edge | Round | Opening | Position |
|---|---|---|---|
| Luff | −20% to 20%, step 0.5 | 0–20%, step 0.5 | 10–90%, step 1 |
| Foot | −20% to 20%, step 0.5 | 0–20%, step 0.5 | 30–50%, step 1 |
| Leech | −20% to 20%, step 0.5 | 0–20%, step 0.5 | 10–90%, step 1 |
In Preview, the luff and leech have Round and Opening sliders plus a Position number input. The foot has Round and Position only; use the foot-profile path described above for its Opening value.
Turn on Show edge guides
In the Shape card’s View section, enable Show edge guides. The guides make the design boundary easier to compare with the rendered surface, especially when smoothing is active.
Move Round
Move right for more positive roach or left for a hollow edge. Use the percentage readout to reproduce a value in the Sail Shape dialog.
Move Opening and Position
Increase Opening to bow the edge leeward. Move Position to place the peak at a different point along the chord. Watch the guide and surface update together.
Checkpoint
The 3-D view changes immediately. If Show seams was enabled, a shape edit clears the stale seam overlay; turn it on again when you are ready to inspect the new seams.
Set the sheet angle
Sheet angle in Preview runs from 0° to 80° in whole degrees. It rotates the displayed sail about the luff chord so you can inspect how it sits to leeward.
Sheet angle is a view-only placement control. It does not change the mould, panel geometry, seams, exports, or 2-D design. If you enable Show boat while the angle is 0°, the app raises it to 15° so the sail separates visually from the centre plane.
A new Code 0 starts at 15°. Every other current sail type starts at 0°.
Set head twist and distribution
Head twist runs from −10° to 30° in 0.5° steps. The foot stays at 0° and the chosen distribution supplies the values in between.
| Distribution label | Observable progression |
|---|---|
| Log law (bottom-loaded) | Applies more of the change in the lower part of the luff, then eases toward the head |
| Linear (even) | Adds twist at an even rate from foot to head |
New designs start with Log law (bottom-loaded). Their head-twist starting value depends on sail type and, for several types, luff length. A Symmetric spinnaker is locked at 0°.
The ↺ control beside Head twist resets the angle to 5°. This is a shared quick reset, not a return to the selected sail type’s File > New value. It does not change the distribution.
Reset the Preview shape controls
The pane-wide Defaults button resets this subset:
| Setting | Reset value |
|---|---|
| Luff Round / Opening / Position | 10% / 6% / 60% |
| Foot Round / Opening / Position | 11% / 5% / 50% |
| Leech Round / Opening / Position | 7% / 4% / 60% |
| Head twist / distribution | 5° / Log law (bottom-loaded) |
| Fullness | 1.00× |
It does not reset Sheet angle, view toggles, skin, mould controls, or heatmap selection. These shared pane defaults are shaped like the preloaded Gennaker example; they are not sail-type-aware. To recover a sail type’s original complete starting design, use File > New and choose the boat and sail type again.
Symmetric spinnaker locks
For a Symmetric spinnaker:
- Preview and Sail Shape combine the edge-shape row as Luff & leech and mirror its Round, Opening, and Position;
- leech-only shape sliders are hidden;
- foot Position is locked at 50%; and
- Head twist is locked at 0°.
The separate Leech chord (mm) remains editable in the Sail Shape dialog. Before relying on symmetry, confirm that Luff chord and Leech chord still match. Section-level symmetry is covered in Profiles and fullness.
Continue with section shape
Edge controls do not set the camber of the horizontal sections between them. Use Profiles and fullness for Depth, Draft, Entry, Exit, profile heights, and whole-sail Fullness.