A boat may compete in a spinnaker class without hoisting a spinnaker.  A boat in a non-spin class may not put up a spinnaker.  Any boat may choose or be limited in putting up sails.  A boat may compete in any class using Main-only or even jib-only.  Not smart, but legal. Code-Zero sails are specifically prohibited, but mostly to avoid adding expense to our "friendly" competition.  A class whose class rules allow them may use them if racing one-design.