... once I raised the mast and tensioned the shrouds I discovered a pronounced depression in the deck at the mast base. The sliding door (head door) was also sticking and could not be opened. I checked the base of the compression post but
couldn't see much. The post, which has a flat plate welded on the end, was surrounded by fiberglass. It was raised above the keel on some sort of platform (which I later discovered was a wood block).
However, I could see that the fiberglass had separated from the sides of the tube (post), and it appeared the tube had sunk a bit. I used a hacksaw to cut off the top of the fg
(fiberglass) box.
 I could then see clearly that the post had sunk about 1/2 inch, and the bottom plate was bent, as if the center of the wood block decayed leaving the plate supported at the
ends.
I wanted to see the rest of the post so I tried to remove the square joinery in the head compartment between the ceiling and the counter. After removing all the screws it still wouldn't budge. It was obvious that the bulkhead, deck, and furniture was taking up quite a bit of the load from the mast.
Now.... I had just raised the mast, and finally had the boat ready for sailing so I decided to raise and
support the post without taking down the mast. The bottom plate had large holes drilled in each end and I hoped to use them to support and raise the post.
First I used a 500 w angle grinder to remove the front of the fg (fiberglass) box. I didn't want to cut it away completely
because I was worried that the wood would completely crumble and let the mast sink another inch or so. Sure enough the wood wasn't much more than powder and pieces. I carefully cleared away the wood just
 under the forward hole and then set a large bolt, head up, through the hole (not enough room to thread it
up though the bottom). I put one nut on the bottom of the bolt (as a base) and a nut and washer just under the plate. Used vice grips to raise the upper nut until it was taking some load.
Repeated the process for the back hole. Tightened both bolts and then cut away the rest of the box. At this point the post was supported by the two bolts (but I think most of the load was being carried by the deck, bulkheads, etc.). I wanted to support the post
in the center so I had a plate cut (5 mm) with a hole in the center. I placed this under the center of the post and used the same bolt/nut arrangement to start lifting it.
 I just tightened the bolts in turn until I had raised the post high enough to eliminate the depression on deck, free up the joinery, and
provide clearance above the sliding door.
Next came the support plates. The compression post bottom plate is 80 x 155 mm (3" x 6"). I had 5 plates cut the same size, each 10 mm thick, and two plates at 1 and 5 mm thick. I had the leading edges of the plate ground with large
chamfers so they wouldn't cut into the fiberglass at the keel, so there would be space to drive 1 mm shim plates between them, and so the upper plate would ride past the weld bead on the underside of the post bottom plate (where it is welded to the id of the post). I started the plates under the back edge; then removed the back bolt; hammered the plates up to the center bolt; removed it; and kept going. There's not much room to work so I used a large piece of steel (3
inch cylinder 7 inches long) that I could swing with my hand to drive and position the plates.
Everything went according to plan. After I retension the rigging I'll refiberglass around the base and plates to make sure they can't shift
sideways.
My recommendation to others is: do the work when your mast is down. Would be much easier, and less risky. However, where there's a will there's a way!
By the way, next time I have my mast down I'm going to replace the post with something a bit heavier, perhaps with a built-in a screw adjustment.
- Jim
You can Email Jim at:
JAdams@qatargas.com.qa
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