Popeye,
Welcome to the world of footydom
There is a Health warning youshould be aware of
Footys are dangerously addictive and you may have a lot of Fun!
In answer to your question: It all depends!
The footy swing rig expert par excellence is Roger Stollery (indeed the
anything swing rig expert) Roger makes the mast and main/jib holders all rigidly bonded together and the mast rotates in a tube fixed to the boat.
He may have a bearing fitted to the bottom of the tube - perhaps a ball on which the mast rests - but as long as it rotates fairly freely all willl be well.
For one meeting I fitted a swing rig to my Razor (its second outing). I made the mast fixed and allowed the "booms" to pivot around it - this seemed to work quite well too (but I'm not a roger S!)
What boat are you making? Have you discovered this resource?
http://www.rcsailing.net/forum1/forumdisplay.php?f=61Where there is a lot of discusswion of rigs, swing rigs and indeed "the whichness of the what"
Happy to answer any questions - or point you to an expert
andrew