A4 Heavy Runner – Racing spinnakers

AWA 115-155°

AWS 14-30 kts

Mid Girth 100% of foot

Med. to heavy cloth

The A4 is for racing downwind in heavy winds, when you don’t want to risk damaging your A2 (the most used sail on any boat). This sail has a powerful running shape, but is about 10% smaller than the A2, having narrower girths and shorter foot length. A4’s are made out of heavy cloth to keep the sail bulletproof, which it needs to be for times that the sail will collapse and then snap full. 

The heart of faster spinnakers is the construction method. The panel layout UK Sailmakers uses is called Matrix, which is a full radial layout that features narrow panels, each oriented to better align the threads in the cloth with the primary loadpaths in the spinnaker. This is the most effective way to reduce distortion and make the strongest sail for its weight.

Each panel is shaped on all four sides in order to create a smooth round sail. For one sail be so versatile, it needs to hold its shape without distorting. Distortion becomes most obvious when  close reaching. Spinnakers made with generic nylon cloth stretch in the middle, causing their leeches to harden or hook; which reduces driving power, creates drag, and increases heeling. The only way to prevent distortion, without using too heavy a fabric, is to use performance nylon spinnaker cloth like those made under the Superkote and Airx names. These materials have the same strength and stretch resistance of one weight heavier standard nylon. 

Spinnaker Painting Program

Use this program to create a custom look for your new spinnaker or cruising spinnaker. Click here to go to the Spinnaker Painting Program.

The Santa Cruz 70 WESTERLY sailing with her A4.

The J/109 Whisky Jack flying with her A4 on a heavy air run.


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