H34 Compression Post repair

[Charlie98117]

OK, I'm finally going to do it. I've got the yard scheduled to pull the mast and a rigger setup to build new standing rigging while everything is apart. I'm planning on following the method used by Heart of Gold and posted in the Owner Mod's back in 2010.

This method involves installing a new SS pipe post that extends through the cabin ceiling to the deck. Ian welded a plate to the top of the new post and installed the old mast step over the top of that. I'm wondering if that plate is really necessary or if the new post just needs to extend 1/8" or so above the cabin deck (to allow sealant space) and the mast step can bear directly on the post.

I have the early version with the large mast step (see photo) and the base is already a piece of 3/8" plate steel. I can do a calculation to see if punching shear is a concern but I'm thinking just bringing the post up to the underside of the mast step is all that is needed for strength. Am I missing something?

 

[BigEasy]

Charlie,
Not sure of the rationale to extend the new post thru the deck. Seems to me that if a leak develops where the post penetrates thru the deck, the whole thing would require removal to reseal. When we replaced the rotted compression post on my Hunter 33.5, we removed the teak trim surrounding the wooden post after removing the mast. Removed the rotten wooden post & thorougly inspected top & bottom support beams. Fabricated a new aluminum I beam post with welded cleats to facilitate replacement of the teak trim and plates welded to the top & bottom of the post. Jacked up the deck from inside (to level deck slightly), and installed the new post inside the cabin only; it did not extend thru the deck. The deck core was not rotten, only the compression post ( 12 years after manufacture) Used the same deck mounted mast step. My only regret was that we should have glassed the hole in the deck beneath the mast step where the mast wiring ran; we should have re routed the wiring externally a few inches above the mast end and used clamshells with grommets to run the wiring into the cabin to allow for simple resealing as necessary without raising the mast. Guess that there are many methods of repairing this common problem; just don't use 2x4s again!!

 

[Charlie98117]

I have to admit I was having some second thoughts along those lines. Making a hole does seem like a risk but the whole concept has to be based on the assumption you can achieve a permanent seal. Given the construction below the mast step includes an embedded aluminum plate that is tapped to receive the bolts from the base plate I am fairly confident that between filling the space with 4200 and cinching up 6 bolts it will be a permanent, watertight seal. From an engineering standpoint I like the idea of the support post being in direct contact with what it supports but perhaps relying on a sealant is the fatal flaw.

I've studied up all the threads on this I could find and understand the problem on this boat is with the wood inside the beam rotting and not just the compression post rotting so the fix has to include hogging out the wood in the beam. I do however see the fix from below approach could be just as good since the fiberglass layup at the mast is substantial so if you carved out all the wood to the underside of the glass then you would substantially have the same direct contact with the mast step. I am concerned that one function of the wood in the overhead beam is to spread the load the post is picking up so carving out for the top plate should allow for some extra width. I think it would be quicker and cleaner to just drill a hole and drop in a new post. Curious to know if anyone else has done it from the top?

 

[BigEasy]

Yes, I had read that some boats had rotted plywood core inside the fiberglass beams above & below the compression post. That is a much more complex situation than I had to deal with.