If you want to have a J30 Class legal boat for one design racing, NA's or resale as a class legal boat, you must remeber the following:

All boat owners are reminded that it is their responsibility to ensure that their boats fall within the Class Rules.
This includes the masts and booms, rudders,
winches, even hand rails. Rudders, masts, etc. must be purchased from an approved builder.

This is a quote from the J30 Class rules:
"It is impossible to foresee every conceivable innovation which may be thought of in the future and to mention every suggestion that has been ruled illegal in the past. When considering anything in connection with the boat or sails or equipment which is not within established practice in the J/30 Class or is not clearly covered by the plans or specifications, you must assume that it is illegal, and must obtain a ruling from the Chief Measurer before attempting it."

Larry Christy
J30 Class Measurer