Merriman car tracks

Hello all,  hoping to gain from the group's knowledge/experience.  Can anyone describe how to remove the Merriman car tracks?  Swan 431, 1978.  The deck wood underneath them needs care/attention.  I can see the backing system is embedded in the GRP under the deck, I can see the slots of the many "screws" are all oriented parallel to the long axis of the track, I can see when I turn some of these screws, there seems to be no systematic tigntening or loosening ( as a threaded system would respond).  What I don't see is how to make any headway in removing the track.  Insights?