Mast Compression Post Rot

CloudDiver · Dec 31, 2016

I hope you have your mast down while doing this... In all seriousness, you don't exactly need to know the exact length to do a correct install on a compression post.
First, the steel adjustable beam will work fine as long as it does not get wet. I'd apply a good coating of sticky waterproof grease to the threads. If you don't have any problem areas of water intrusion it will work, but consider that you must have a leak somewhere since the original compression post rotted. Consider all possible areas of water ingress and also consider how you will reattach the teak trim.
Second, getting the post to the correct height is a simple matter. With the mast down place the post into position and adjust it to fit. Keep going up until it has firm upward force on the cabin top below the mast foot. You want it in there very firm, but if you start flexing the cabin top up too far and hear fiberglass being to creak and pop you might be going to far. The idea is to leave no room for the rigging force to flex the cabin to downward and appropriately transfer the force to the compression post.
Third, some details to consider... Once you get the correct setting of expansion on the adjustable beam can you 'lock' it? Maybe safety wire will do the trick. Also consider how firm the top and bottom plates on the post are 'seated' to the cabin overhead and then in the bilge. Is there proper support there to transfer forces and a secure footing for the plate to sit without any slip?
If you decide to do this we'd all love to see some pictures!

Jackdaw · Dec 31, 2016

The first one was ruined because it got wet, and was made stupidly from a material that suffered when it indeed got wet.

Gee.. its a boat. Who would have figured it might get wet???

Why make that mistake again? Fix it right.

heritage · Dec 31, 2016

This shows the base of the compression post on my Hunter 27. It appears to be a pressure treated 4x4 post that is clad in teak plywood. My post is in good shape, but if I had to change it I would replace with another 4x4 post. Seal any leaks, push up the ceiling a bit, and cut the new post to length. I would not mess with a metal adjustable post except maybe as a temporary jack to raise the ceiling.

jack to raise the ceiling.

kloudie1 · Dec 31, 2016

Attached picture shows the original marking on my post, on the bottom right corner. It is marked 70 inches and when I measured it, that is the dimension I found. .. Mine had rot only at the very top so I removed the rot and carved a plug to replace the rotted stuff.. The green stuff in the wood is copper naphthenate, a wood preservative that I soaked the interior of the post in to stop any further rot. I don't think I'd use one of the adjustable jack stands.. It would probably be OK; I just cringe at the thought of something that could possibly unscrew ..

splax · Dec 31, 2016

Hello,
I have a '87 H34 and did the compression post a few years ago. Look at my thread "compression post repair failure" for some reliable guidance from others on how to do the job. The length/height of the post and other information is in there. I don't think you want to use steel because of corrosion issues.

Mark Maulden · Dec 31, 2016

Use a section of freshly painted mast for a new post..should be able to find an old mast somewhere..can also route wires through it..

EV21 · Jan 1, 2017

How about something like fiberglass? Not sure about strength but should be fairly impervious to water.

David in Sandusky · Jan 1, 2017

First, a couple of don'ts:

Don't use regular steel, especially in a salt water environment.

Don't use pressure treated wood! In addition to releasing poison into your cabin for years, treated pine has about the worst dimensional stability of any wood - the last thing you want to hold up tons of compression when you tune your rig.

According to JC II, (http://forums.sailboatowners.com/index.php?threads/compression-post-rotten.170466/#post-1200913) good woods for compression are mahogany, teak, and white spruce, in that order. White spruce is probably the most cost-effective. An advantage of wood is the ease of tieing the compression post into the bulkhead (if this is the original design, they work together to maintain hull shape under the dynamic stresses of sailing.)

Aluminum and stainless steel will also work with suitable end plates. There is an aluminum project in the archives.

Do unload the hull by taking down your mast for the replacement project.

JCall · Jan 1, 2017

EV21 said:
How about something like fiberglass? Not sure about strength but should be fairly impervious to water.

There would be some engineering involved with designing an all fiberglass compression post. Fiberglass is meant to be loaded in tension where the load follows the glass fibers. Think of pushing a chain up hill. In compression, you are expecting the epoxy matrix to take the load. Wood by nature of the tree supporting its own weight, lives under a compression load. Factor in wind loads when the tree is leafed out and the forces are significant.

I would use a hardwood such as oak or maple, cut it to length, then encase the wood post with fiberglass to seal out water intrusion. Then I would use a wood veneer to cover the new post because I like the beauty of wood.

The only design change necessary is to seal the inevitable water away from the new post. Wood/fiberglass is easy to bond into place so the post will resist slipping under a dynamic load. Use of steel or aluminum offers challenges in fastening in place. Corrosion of the aluminum or steel would be next.

The new wood post does not have to be a solid 4x4, it could be laminated using an epoxy such as System 3 T-88 or West System.

Lastly find the source of the water intrusion and seal it.

Charlie98117 · Jan 1, 2017

I'd agree that regular steel is a bad choice for a marine environment but I think you can also find those lolly columns in aluminum which would be better. Stainless is best or just stick with wood. Is your overhead beam crushed?

I just finished taking mine apart. I have an 83 with the large mast step and didn't see any evidence of water intrusion, just crushed wires because the slot in the compression post didn't align with the conduit from the mast step. I was planning to install a new stainless pipe column with plates at each end but decided to fix the wire issue and just put it back together since there was really no problem.

Blindnavigator · Jan 3, 2017

Good suggestions all, tho I would shy away from any metal, even in fresh waters.
After finding I couldn't close the head door due to cabin roof sag, did the following on a Pearson 30:
1) cut/grind away glass tabbing at post base to assess damage
2) must have mast down
3) cut away a few inches of rot at bottom of post-straight cut is important.
4)use 2x4 or similar and jack to gently( and I mean gently) raise cabin roof
5)cut oversize block of rock maple, white oak, or ironwood ( if you can find it) grain direction is important in compression posts
6) force fit block, shaving as necessary, at bottom of post.
7) liberally epoxy and tab in place after removing jack to secure and waterproof. I also drilled and inserted two screws at angles from old section into new.
8) replace mast, tune, go sailing.
It hasn't budged a mm in five years, and could easily be replaced if needed. Good luck.

Patrick Lombard · Jan 3, 2017

Here is what I did.

http://hunter.sailboatowners.com/mods.php?task=article&mid=25&aid=7376&mn=31_83-87

SFS · Jan 3, 2017

Since you've posted this in two different places, you may want to ask a moderator to combine the two threads.

markwbird · Jan 3, 2017

I've done this repair as have many others on this site. As Jackdaw noted it was built poorly. However, in my case as is many others, it was not wet. It's just that the bearing area between the top of the compression post and the wood cross beam is absurdly small. It is the cross beam that crushes not the compression post(usually). Using the steel post does not address this. Look at some of the fixes on this site and discuss with the folkd who have done this and develop a plan.

David in Sandusky · Jan 3, 2017

White spruce is a lot lighter than oak or maple And similar in compressive strength and stiffness.

Dave Pawloski · Jan 4, 2017

Barn-dog said:
My thanks to all for your fine thoughts and comments! I like the steel post, due to the ease of adjusting it for the right fit, but I am uneasy about the thought of it possibly becoming "unadjusted" over time. I could squirt some 5200 into the adjusting threads. Also, there's the possible corrosion that could occur on the bases of the steel post. Of course, I would seal any area of water intrusion around the mast, and I could apply barrier coating to the steel bases, followed by Rustoleum paint. I'm not certain that I want to go with steel, yet. I'm trying to find a mill in my area to get a quote on a 4X4 white oak or spruce post.
If I go that route, it still may be good to attach plates to the top and bottom of the wood post for better support. I could have S.S. plates made for that. I know a good welder who works with Stainless.
Anyhow, I can't really do this fix until I uncover the boat in March, and have the yard pull the Mast . She's on the hard, now.
I would also like to re-route the wires, away from the mast at its base, so they don't come in contact with the post. I'll take before and after pic's and keep you all posted, as I do this.

Dave Pawloski · Jan 4, 2017

Seems like a hugely common problem on the 84-87 vintage Hunters.
The compression post on my 1985 H-31 died of rot about two years ago. Apparently there was water intrusion through the opening in the cabintop for the various wires in the mast.
LSS, I temporarily used 2x4 braces from the stringer on the cabin sole to the overhead stringer..... on both sides of the compression post (did not need to remove the mast). Tapped them in with a rubber hammer to ensure that the cabintop stringer was pushed up as far as it wished to go. I then installed a new oak compression post (trimmed to the exact necessary vertical height and with a channel for the wiring from the mast routed down the appropriate side), screwed top and bottom into the upper and lower stringers. I then removed the 2x4 braces from either side and completed the installation with new teak wrap-trim that I had made by a local custom woodworker.
The next time that the boat was in the yard for service, I had the mast removed and the opening in the csbintop sealed properly.
Everything works great.

Mast Compression Post Rot

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