If I can avoid the hire of a crane I would like to, that said given the water level right now I may not have a choice...
unfortunately the boats previous caretaker has neglected the trailer so much that it is beyond economical repair.
I have to either borrow/hire a similar trailer or use the existing trailer as little more than a cradle and but boat and trailer onto a car recovery transporter truck and then transport it.
as for dropping the mast;
I had wondered about attaching two rope to the top in a 'V' formation to lower the mast and then lash the sheets and control lines together beneath the deck to act as a kind of stopper then pad the whole bottom end of the mast with lots of fabric to prevent damage..
if the rope beneath deck were lashed together that would almost act as a crude pivot. if sufficiently padded that should provide enough protection for the deck whilst the mast is lowered by the two lowering ropes attached to the top of the mast.
The bridge idea is something I wouldnt have thought of but the only bridge nearby is at the mouth of a rather large river (with a current) so that might make life move difficult.
that said... if the top of the mast was somehow secured to the bridge and then the boat moved away... then the mast would then pivot from the bridge rather than the deck and could possibly be lifted off more easily from there. hmmm...?