Join Date: Feb 2000
Location: Annapolis, Md
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One very important note, there is no relationship between your hull form and an IOR hull form. The IOR rating rule produced hull forms which were tender and which could point very high up wind and very deep down wind but which were not well suited for reaching. Consequently, IOR main and jibes tend to be cut very flat to reduce heeling and take advantage of their ability to point higher than other designs and IOR spinackers were cut full with huge head girths for deep downwind angles.
The Irwin cruising models were far more moderate, and had rigs and hullforms that were not all that great upwind or dead downwind, but which were optimized for reaching so their jibs and mainsails need to be cut fuller, and their spinackers cut flatter than an IOR influenced design.
A quality sailmaker would be aware of the different needs of an IOR boat vs a more moderate cruising boat. If you come into a quality sailmaker and tell them that you have an IOR design, the sailmaker will make you sails that would not work well with your boat.