I have been restoring my 78 Catalina 22, and I was trying to find information on how people have painted the bottom apart from lifting it off of the trailer. Finding no information or write-ups I figured I'd put up my own to help out the next guy. I hope this will be as useful to someone else as it would have been to me.
The first thing I did was lower the trailer jack all the way down in the front, next I stacked cement blocks under both sides in the back and but a plank between them to form a cradle. Next, i put a longer plank running towards the front of the boat and jacked the trailer back even(a good portion of the weight aft end of the boat is now on my cradle). with the jack up a little higher yet, i now block under the front end of my planks, and let the trailer back even once again. Now i have 2 planks running down either side of the boat on which to carry its weight.
Now you want to do this one side at a time. Place a floor jack(or bottle jack) at either end of one of your planks. Jack them up slowly and evenly until the hull is just off of the bunk. Remove the bunk( this required an impact wrench on my trailer). Now shim between your blocks and your plank so not all the weight is on the jacks, and make sure the boat is stable. Now you are ready to paint.
When you are done with the first side, simply replace the bunk, and repeat the process on the other side.