JESUS CHRIST,IT TOOK ME 10 MINUTES TO GET BACK TO THIS POST. Anyway.
This is what we used to repair the bottom of a 16' Ashcraft ripoff. It may be a little hairey on a 20' boat.
All we did was back the boat between two trees, hoist the front above the trailer, loop a chain around this at the rear and hoist it high enough to get the trailer out.
One person could easily rotate the boat.
Oh attach to the lower bolt holes.