Sailho, How did you jack up your mast. Did the loose turnbuckles give you any trouble with the mast not being stable?
I have finally gotten some time to post up pictures of when I jacked up the cabin top to do the repair on the compression post on my Islander 28.
I had my mast down for my repairs, but could be done with the mast up if done properly. The mast and spreaders weight about 125 pounds, not as heavy as you think, just tall and awkward. The foot plate the mast sets on has a 1/4-3/8 inch lip the mast extrusion fits over. This will keep the mast from slipping out from under the rigging should the rigging become loose for whatever reason. Keep in mind that is not much margin for loose rigging.
At your own risk you can gradually loosen the rigging slightly, jack up a little, check the rigging, loosen slightly, jack up slightly, and so on, until you can remove the post. Reverse after repairs
The mast only weights about 120 pounds. I would still run lines from the spreaders to the rails port, starboard, forward and aft. I would have these lines fairly relaxed. I would remove all sails and the boom.
The biggest problem is if you want to replace the counter top the metal tub sets on. You have to remove the tube completely and place a temporary 2x4 or 4x4 the correct length to support the cabin top and be able to move the jack set up. This allows you to fix it all. The bear is getting the tube out with the wires running through it. I re-stepped my mast with all new wiring too.
I even drilled each end out to be the same size on the tube. Then put in a PVC tube through the holes and glued them in. Sure made it easier to fish the wiring through the tube. Imagine a pipe with 1/4 wall and to plates welded on each end, the only 1 inch holes in the plate. You put the wire in and it hits the plate at the bottom.
Any way you can fix the weakest part of the compression post, the floor area, without much hassle. Just requires right tools and time.
here are my pictures of how I jacked up my cabin top. Remember, shouldn't have to much load on the jack if the mast is removed. You can hear when you are getting close to original height, head bulkhead will creek some where it is tabbed.
Keep an eye on the set up and boards getting out of alignment. You don't want them kicking out from under the jack. I put a piece of 3/4 plywood along the sauté and a 2x4 to keep the jack up right to accommodate the lateral force. It doesn't take much to move the top.
Jack from my Toyota or a bottle jack
Side bracing. You will need some wood door type shims for leveling the 2x4 on the sole, shown on the top right corner of the 2x4.
Jack in place with 2x4 to cabin top. I had to use some additional 2x4 under the jack to get the correct height and have travel in the jack.
Cabin top area
Once the top is at the height you want measure the distance from the top to the 2x4 next to the jack base. Cut a 2x4 length and put it next to the jack set up, using shims to adjust fit. Then remove the jack set up. You could put in a few screw attaching the 2x4 to the floor 2x4's and the 3/4 inch plywood at the top, prior to removing the jack of course.
This worked for me, there maybe better ways, but this seemed pretty easy.
Good Luck and work safely!