cabin top sagging under mast, 31 bombay clipper

[abode]

I have a 31 Bombay Clipper 30 yrs old. I have noticed the cabin sole under the mast is sagging. The boat has a compression post that is set ahead about 8 inches of the mast. I have read this problem is not uncommon for many boats. My proposed fix is to attach low on the compression post and build a truss like structure up to the cabin sole with an adjustable length that I can use to jack up the sole to my liking. This places a post under the mast and transfers all weight where it was designed to go. Does anyone foresee a problem with this? W

[MARC2012]

Would drop the mast myself,if done with mast in place and tight standing rigging will be a test of unstoppable force meeting immovable object.marc

[fordo]

I suspect that the support under the compression post has failed in some way, possibly rotted. The compression post support is like the mast step on a keel stepped boat, subject to the same stresses. I would take out the post(mast off, of course), and find out what the problem is. I would not put anything adjustable in a permanent solution. It may "adjust" itself while you aren't looking... not a good thing in your rigging. Ford

[JimsCAL]

I agree with fordo that there is something wrong with the compression post, probably at the bottom in the bilge. You need to find out what the problem is and fix it.

[abode]

Maybe but I don't think so. The cabin has not deflected at the compression post but behind it. The sag is behind the post. Completely through the fiberglass top directly below the mast. If the sag was at the post I would be inclined to agree. However the post is set next to the salon/front birth wall and I can see there is nothing giving there. This boat is a new /old boat to me and this appears to be a chronic problem that has never been corrected. There may be some weak core beneath the mast but this boat is supposed to be coreless solid fiberglass lay up. I will drill and check. As long as the deck is not compressing I think I can release some tension from the rigging and raise the post incrementally. Repeating this process until things are back where they should be. Then a weld or pin can secure the height. Thanks, Not a Brystol repair for sure but good enough for an old Coonass from the oilfield.

[tommays]

I think you will be seeing soemthing like this in the near future

[JimsCAL]

I note your post says the cabin sole is deflecting while the title says the cabin top. Which is it?

[abode]

My mistake, cabin top

[ccriders]

Adobe,
When I was looking for a boat I found several models with deck stepped masts with the cabin top/deck sagging and in some cases fractured. Depending on the design, jacking up the compression post will not provide an adequate fix. In all probability the deck core is rotted and will have to be rebuilt (see Tommays photo). You may also have problems with a bulkhead. A complete inspection of the compression post footing is also required. Without repairing the underlying problem you might be setting yourself up for a catastrophic rig failure.
Good Luck
John

[abode]

I completely agree. But what I dont understand is this. The cabin top is not sagging at the post. Everything is fine at the post. The sag is approximately 8 inches behind the post. This is where my mast actually sits. It is not directly above my post. I have removed a decorative cap at the post and cannot find any moisture and with vigorous probing with a screw driver am not finding any rot. I do not propose doing anything with the compression post as everything in that area seems perfect.
it appears to me the top after 30 yrs of handling the mast with minimal support has started sagging. My thought is to not adjust the compression post but leave it in place and use it to be the long base of a truss made of matching 2" stainless, attaching at the bottom of the post. rising at a diagonal over approx 6' and out 8" then turning back parallel to the compression post the last 10 " or so with an adjustable end. probably a heavy screw that can be backed out to apply upwards pressure counteracting the mast weight. the load is transferred though the truss back to the compression post which should have been designed to handle this anyway.
i do have some drilling to do at the sag point to check for core rot (i still believe there is no core, all literature I have seen states the deck is solid fiberglass) at the sag point. There is none at the post itself.
I'm not trying to be stubborn but outside of possible core rot ( I will determine this when the weather improves) no one has gotten through to me how this is a compression post failure. As there is not a problem at the post.
I appreciate the replies.