Questions about IRC Code Zero Sails....

 

There are quite a few misconceptions as to what an IRC code zero sail is and at what angles it can be used.

An IRC code zero is measured as a spinnaker, so it must have a mid-girth measure- ment that is at least 75 percent of the foot length and a leech length that is no more than 95 percent of the luff length. 

Volvo 70s are often seen sailing upwind with what many people call a code zero. However, these upwind sails have mid-girth measure- ments that are 55 to 65 percent of the foot length. Because these sails don’t have to support all this extra area, they can be designed flatter and used at tighter angles.

A typical IRC code zero needs a lot of additional shape in order to support the large mid girth.

These sails are difficult to design; you want to build in just enough depth to support the girth and prevent the leech from flapping while still getting the sail as flat as possible so it can be carried at a tight angle. If done right, how- ever, a code zero can be quite advantageous for boats with non- overlapping jibs in point-to-point races. But don’t think for one moment that it will sail upwind; 90 degrees true wind angle is as high as they’ll go.

The Technical Stuff:

IRC definitions define a spinnaker as

Spinnaker: RRS 50.4 shall not apply. A spinnaker is defined as a sail set forward of the foremost mast with half width (measured as a spinnaker) equal to or greater than 75% of foot length and without battens.

Thus, if a sail satisfies the definition of a spinnaker (ie half width is equal to or greater than 75% of foot), then that is what it is: a spinnaker. Any other sail is a headsail. ‘Code zeros’ are nearly always intended by the sailmaker to be spinnakers. Measurers should however beware. If however a sail has battens, defined in IRC as Any material added to the sail, as either a removable element, permanent stiffening, or other contrivance, the purpose of which is to support and/or stiffen the sail. then it is a headsail rather than a spinnaker, irrespective of what the dimensions are.