This is concerning a Catalina 30 1985 sailboat. This February when I was doing work on my boat and getting a survey done, the rudder moved freely. Two months later, after sitting in its usual dock location the rudder is no longer moving except for an inch as if it is seized up. The wheel does not move. The emergency tiller does not move. A diver went down and cleaned what little barnacles were there and he was unable to move the rudder underwater. He changed the zincs and the two original ones were still fine. I am not on the boat currently as with the Corona Virus I am stuck in my home in the US however; my dad who used to own a Catalina 27 and lives nearby has looked at all the components from the wheel to the stuffing to box and finds nothing jamming the mechanism. My husband and I had changed the chain in the wheel pedestal in 2015. So I ask, does anyone have any idea what it could be? We are about 5 nautical miles from the nearest dry dock. Thank you.