A Heavy Weather Jib's sail area is limited to 13.5% of the height of the foretriangle squared by ISAF; but UK Sailmakers believes that this area is too much for most boats in storm conditions. Typically a sail with an 85% luff length and 85% LP defines a good No. 4. ISAF regulations state that this sail cannot have reef points and they recommend not using high modulus material. However, UK Sailmakers believes if you are going upwind in 28-35 knots, the sail needs to be made of low-stretch materials with battens for an effective shape.
If the heavy weather jib is made to fit a luff-groove device, the sail must have an alternative means of being attached to the stay. The most common alternative method is to have grommets along the luff so that you can tie the sail to the stay.