Over the past 20 years or so, the term 'code zero' has often been mis-applied to describe a variety of large asymmetric sails used on different points of sailing. However, the generally accepted definition is that it is a sail which, under most racing rules, rates as a spinnaker but is set when sailing upwind in light airs and perhaps on a beam reach as it gets windier.
For IRC racers, they are especially useful for offshore and round the cans races.
Alan Harris-Guerrero of Sail Shape explains: “IRC yachts love these sails as they don’t affect their upwind/ reaching sail area on the IRC certificate, so in light to medium airs an IRC yacht with a small jib power-reaching can hoist a code zero giving a massive boost in sail area, especially if they are sailing too high to run their A3 asymmetric.”
For cruising, sailors are often uncertain as to which kind of sail is the best choice: is a code zero the smartest option or not? Mark Woodford of Jeckells the Sailmakers emphasises that it is important to first understand which sail is best suited for the type of sailing you're most likely to do. He explains: “A code zero is a flat free flying sail designed for close reaching angles. Many cruisers confuse code zeros with asymmetric sails, thinking they are for sailing downwind when really the benefit comes in increasing upwind sail area.”
Under IRC rules, and indeed World Sailing’s Racing Rules of Sailing, the difference between a headsail and a spinnaker depends on the mid-girth measurement as a proportion of the foot measurement: less than 75% and it is a headsail, which incurs a significant rating penalty for any area additional to that of the next biggest headsail; 75% or more and it is a spinnaker, for which there is no penalty as it will be smaller than a conventional spinnaker.
The code zero first appeared in the 1997-98 Whitbread Round the World Race in which Paul Cayard’s Whitbread 60 EF Language, the eventual winner, carried one from the start of the race. “The rules for the Whitbread boats at that time called for 60% mid-girth measurement,” says Peter Kay of One Sails, “but Cayard found a way of going upwind with it.” Seeing how successful it was, Cayard’s competitors had similar sails made during the course of the race.
“Anyone who saw the boats approaching the finish, using code zero headsails/spinnakers up the Solent,” wrote Bob Fisher in Yachts & Yachting, “might have been forgiven for thinking that the Whitbread 60 class was a masthead class with overlapping headsails instead of one with fractional blade jibs.”
Since then the trend towards bigger mainsails and smaller jibs, partly resulting from the demise of the IOR rating system which allowed 150% genoas without rating penalty, has led to a huge increase in the popularity of code zeros. “Boats with non-overlapping headsails see the biggest benefit from a code zero as they fill a large gap between upwind jibs and downwind spinnakers,” says North Sails’ Neil Mackley.
“As a general rule which applies to most boats,” explains Kevin Sproul of Ultimate Sails, “if a boat’s conventional headsail is 40 square metres and the spinnaker is 100, the code zero will be about 70.”
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