December 8, 2015
Quantum Expert Answer
Code Zero spinnakers are only made in an asymmetrical configuration. This is because they are more nearly genoas than spinnakers. The reason they work at close apparent wind angles is because like a genoa, their shaping is relatively flat, and has a distinct airfoil shape with defined entry and flat exit. Their geometry is asymmetric as a result, with a longer luff and shorter leech. The problem of making a very close winded spinnaker is further complicated by minimum girth requirements. Most handicap rules including PHRF, IMS, and MORC, require a minimum girth of at least 75% of the foot length. The bigger a sail is, the harder it is to make flat enough, and genoa-like in shaping.
What the rule makers are after is limiting the construction of this type of specialty close reaching sail. The sentiment is typically that there is no sense in promoting an arms race, which would require every boat to have a Code Zero or specialty close reaching sail. The Volvo 60 Class, where these sails were first developed, does not have the same stringent minimum girth requirements, and have big budgets. (A Volvo 60 typically carries eight asymmetricals, each designed for a specific wind range). The original version of the Code Zero is actually much flatter and more close-winded than the sails subsequently developed for handicap rule use.