Calculator Inputs
Enter your sail size, typical wind conditions, and connection geometry. The tool estimates corner loads and suggests a minimum WLL target for each corner’s hardware.
Example Data Table
These examples show typical inputs and the kind of outputs you’ll see. Your site conditions and hardware ratings can vary widely.
| Example | Shape / Size | Wind | Corners | Corner tension (approx) | Min WLL target (approx) |
|---|---|---|---|---|---|
| Patio shade | Rectangle 4.0 × 3.0 m | 60 km/h, open | 4 | ~4–7 kN | ~12–21 kN per corner |
| Garden triangle | Right triangle 4.0 × 3.0 m | 50 km/h, suburban | 3 | ~3–6 kN | ~9–18 kN per corner |
| Coastal deck | Triangle sides 4.0, 4.0, 4.0 m | 70 km/h, coastal | 3 | ~6–11 kN | ~18–33 kN per corner |
Formula Used
- Area: rectangle A = L × W; right triangle A = (base × height)/2; triangle (3 sides) uses Heron’s formula.
- Wind pressure: q = 0.613 × V² where V is wind speed in m/s, producing N/m².
- Projected area: Aproj = A × cos(tilt) (simplified), with a minimum floor for stability.
- Total wind force: F = q × Aproj × Cd × ExposureFactor.
- Corner tension: T ≈ PreTension + (F / corners) × DistFactor / sin(tieAngle).
- Minimum WLL target: WLL ≥ T × SafetyFactor (per corner).
- Total cable/webbing length: sum of each span plus allowance per corner.
How to Use This Calculator
- Select your sail shape and enter accurate dimensions in meters.
- Choose the number of corners that match your sail’s corner rings.
- Enter a representative wind speed (use typical gusts for your area).
- Pick an exposure level that matches your site openness.
- Set tilt and tie-down angles based on your planned geometry.
- Choose a safety factor; 3.0 is a common baseline for outdoors.
- Enter the span distance(s) from each corner to its anchor point.
- Press Calculate Hardware to view results above the form.
- Use the CSV/PDF buttons to save a copy of the latest result.
Professional Notes
Use these points to interpret the outputs and plan a practical, safe installation.
Design inputs that drive load
Accurate sail area is the first control on hardware demand. A larger planform increases projected area and multiplies wind force. Corner count matters too: the same force is shared across three or four connection points, changing the expected line tension per corner. Anchor span affects material length and adjustment, not wind force. Add allowance for turnbuckle travel so you can tension evenly, and keep at least one full thread engagement after final adjustment, always at corners.
Interpreting wind pressure results
The calculator uses a common pressure model q = 0.613 × V², with V in meters per second. Pressure rises with the square of wind speed, so a small increase in gusts can add significant load. The exposure factor accounts for site openness and helps you compare sheltered gardens to coastal decks. A tilt angle reduces projected area using cosine.
Corner tension and geometry effects
Corner tension is not equal to wind force divided by corners. Tie-down angle controls the mechanical advantage of the line: lower angles reduce the vertical component and require higher tension to resist the same load. This is why the model divides by sin(tie angle). Pre-tension is included to reflect tightening with turnbuckles, which improves fabric stability but increases baseline demand on fittings.
Selecting hardware and anchor points
Use the minimum working load target per corner as a selection threshold for turnbuckles, shackles, and anchor hardware. The safety factor multiplies estimated tension so fittings remain within rated limits under gusts. Compare ratings in kN and the approximate kilogram equivalent, and pick the next higher class. For posts, confirm embedment depth and footing size; for walls, confirm the structure behind the surface finish.
Maintenance and operational guidance
Outdoor hardware benefits from routine inspection. Check for corrosion, thread galling, elongated holes, frayed webbing, and loose fasteners. Re-tension gradually and evenly to avoid twisting the sail. In extreme weather forecasts, taking the sail down reduces peak loads and extends service life.
FAQs
1) What does “minimum WLL per corner” mean?
It is the minimum working load capacity recommended for each corner’s connection line and fittings after applying the chosen safety factor. Select turnbuckles, shackles, and anchors that meet or exceed this value.
2) Should I use average wind or gust wind speed?
Use a representative gust value for your site, because gusts drive peak loads. If you only know average wind, choose a conservative higher value to avoid undersized hardware in sudden weather changes.
3) How does tie-down angle affect the result?
A smaller tie-down angle increases line tension quickly. Keeping angles in a practical range, often around 20–35 degrees, reduces amplification and helps hardware operate closer to its rated capacity.
4) Why does the calculator ask for exposure?
Exposure reflects how open the site is to wind. Open and coastal areas can experience stronger, less turbulent flow at the sail, so the exposure factor increases estimated wind force compared with sheltered gardens.
5) Do longer spans to anchors reduce the load?
Span length mainly changes material quantity and how you route the connection, not the wind force itself. Loads are dominated by wind, angles, and pre-tension. Focus on anchor strength and geometry first.
6) When should I take the sail down?
Remove or furl the sail when strong winds are forecast, during storms, or when hardware shows damage. Reducing exposure during extreme events is the most effective way to prevent sudden anchor or fitting failure.
Recent Calculations
Stored in your browser session (up to 10 entries).
| Time | Shape | Area (m²) | Wind (m/s) | Corner (kN) | Min WLL (kN) |
|---|---|---|---|---|---|
| No saved calculations yet. | |||||