Encapsulated keel means that the keel was manufactured as part of the hull, then the lead was put in, then the rest of the boat assembled. One result is that you don't get the "Catalina grin", as I have heard the separation line betwixt hull and keel referred to. Would love to know what those "bolt-heads" are, though. Good luck and welcome to the forum.
Bill Coxe, O40, New London, CT