Properly tensioning a shading system can be complicated, but it doesn’t need to be impossible. Getting it right is critical to the stability and durability of the structure. Too little tension, and the structure risks damage from wind or pooling water. Too much, and the attachment points may break, supporting structures may bend, and the fibers of the rope or shade cloth can degrade, creep, or create injury risks in the event of a failure. The following four considerations will help ensure a safe, effective, and long-lasting shade structure.
Shade sail sagging from low tension is also undesirable in calm conditions because rainwater on an outdoor shading system can collect and put far more weight on the fabric structure than it can safely support.
Another factor to consider is rope creep, defined as an unrecoverable stretch of the rope. High tension in shading systems exerts a constant pulling force on the soft goods. Over time, this force can cause permanent stretch that will gradually loosen the ropes and fabrics, requiring re-tensioning or replacement. The most successful designs will use ropes that have a minimal tendency to creep under tension, such as Robline’s Ocean 5000.
(Source: Formfinder - Typology)
Triangle shades always remain flat as it is not possible to create a hyperbolic paraboloid shape with only three corners. This means triangular shade structures are more prone to flapping and holding water than hypar structures. At least four tensioned attachment points are best for the longevity of shading systems.
Sometimes, both pulleys and snap hooks are used on the same shade structure. The snap hooks are quick and easy to use while the mechanical advantage provided by the pulley system allows for adequate tension to be pulled on by hand.
There are many important factors to consider when specifying a tensile shading system, but the above points should get you on the right track towards an effective and reliable shade structure.