I'd recommend getting a fiberglass deck level antenna as a backup antenna for your vhf, and fix your mast antenna. I'd bet you'd get a good response to radio checks when you connect the fiberglass deck antenna to the vhf. The problem with the mast antenna sounds like a corroded cable, connections, or antenna.
Gemini Catamaran Split Decision
I already have a 6 ft whip and a 2nd VHF at the helm, as well as a handheld. So it is a question of getting the darned thing to function, not an immediate safety question.
The VHF cable down the mast was installed at the beginning of the year. The only thing remaining is the balun coil at the base of the Shakespeare whip on the masthead. The cable was purchased with the masthead connector installed, so if there is a problem it is likely to be with the soldered connector I installed at the bottom of the mast, or with the VHF antenna itself. Could also be the splitter for the FM that is faulty...
I can check most of these things out, but I really would like to know what the DC resistance should be of the cable+antenna. If someone could measure it on a working system that would be a big help.