Box rule: The name comes from the simple concept that a boat’s hull and sails must fit inside the measurements of a box. If a boat fits within the box, it meets the rule and can race without time allowances against other boats that fit the box. The Open 60 rule and the C-class catamaran rules are good examples of classic box rules. The Transpac 52 is a more sophisticated box rule that’s intentionally type forming to create the type of boat many owners want, i.e. fast, fun, stiff, simple, safe, lots of sail, etc. Handicap rules: Purists point out that the term “handicap rule” should only be used to describe rules rating boats based on observed performance. These rules are usually administered locally, but some, like PHRF, have national guidelines. Measurement rules: Americap and IRC are measurement rules, since ratings are calculated based on measurements of the boat. Examples include CCA, IOR, IRC, IMS, Americap. Measurement can be a complete wanding (computerized measurement) of the hull that’s entered into a VPP (a computer program that predicts a boat’s speed at all wind-angle and wind-speed combinations based on its measurements). Or measurements can be taken at points on the hull, and the rule can be a simple formula. Either approach yields a measurement rule that generates one or more ratings.
