I have a few questions for you. Do you have a roller trailer or a flat bunk trailer? Four or five sailboat stands? Block and tackle? Fifteen or twenty wooden blocks? Hydraulic jack? Taking my O'Day 222 off my roller trailer was always a simple task with the aid of four boat stands, a rope from a tree to the transom of the boat with a block and tackle in between to tweak it a little, along with the 8X8"X 4' blocks. The towing vehicle mealy pulls the trailer out from under the boat until the keel is exposed behind the trailer. The keel is then blocked up. Four sailboat stands, two on each side near the stern keep the boat from tipping. Wood blocks are placed parallel to each other and criss-crossed under the stern, for safety reasons and extra support. If more height is needed in the bow portion of the hull, a hydraulic jack can be used to lift the bow from the trailer, and small blocks are placed under the keel to take up the gap and attain the height needed. Then the trailer can be pulled out completely. Two of the sailboat stands can be removed and placed about 6 or 8' forward of the rear stands. More blocks should be placed under the bow, in front of the keel in the same fashion as the ones on the stern. Sailboat stands aren't made to lift boats, but my Brownell SB-3 angled sailboat stands can lift my 222 with no problem. The stands can be raised evenly and more shoring can be added under the hull as the boat is raised. The keel shoring blocks can be removed and the centerboard can now be let down. In order to get the boat back on the trailer, you need to reverse this procedure, and the trailer is lined up to the bow, with out the towing vehicle. The winch is hooked to the bow eye, and the trailer is winched under the hull of the boat. If you have a flat bunk trailer, more jacking and blocking under the forward portion of the hull is involved, and it's a long slow process but doable. It goes without saying that doing something like this is very dangerous and it's a good idea to have someone with you who is familiar with rigging, a power company lineman perhaps. You may be able to just get half the boat off the trailer and be able to get at the exposed keel to let the centerboard down. Last spring, I removed the centerboard on my boat and painted the inside keel slot as well as the whole bottom of my boat by doing what I have just described. I enjoy doing my own work on my boat in my yard, and this is why I do it, plus I've saved a few bucks through the years. My newest project right now is re-doing all the wood inside the cabin of my boat. I removed every piece of wood in the cabin and I'm staining and varnishing. Every year I take on a new boat project. Good Luck!
Joe