I have a white fiberglass antenna at the top of the mast installed by the PO. it's about 3 feet long and 3/4 inch in diameter. It appears to be connected to a very robust coax cable running  inside the mast- which was cut and has no connector on the end and has never connected to anything. The coax cable is about a half inch in diameter and extremely stiff, and  gets in the way of all the other cable connections. The PO owner had XM radio, but that antenna is mounted on the stern. I had Loran on our previous boat, but that antenna was much longer at 5-6 feet in length and I don't recall it using such a stiff cable.

The mast head also has our VHF antenna, and a lighting dissipator  which has no cable. The mystery cable seems too large for an AM/FM radio antenna. The PO sold me the boat in 2013, previous to the Starlink era and those don't employ long tubular designs anyway.

Any guesses on what this antenna might have been used for? I'm planning on removing it, and pulling the cable to give me more room inside the mast.