I just won a Crusade for Beirut in about three or four months of fighting by using my Medieval Blitzkrieg shock-and-awe tactics (Sea Transport => Doom-Stack => Assault => Repeat).
The Crusade was perfectly timed, from my point of view. My King is in his mid-fifties and probably won't last much longer, two of his sons were old enough to take on Crusade with him along with most of my important vassals; so when my heir inherits the kingdom, he will get the +30 "fellow Crusader" bonus with most of the powerful vassals in my realm. That should make for a fairly smooth transfer of power.