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Old 13-05-2015, 15:15   #1
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Compression Post Replacement in Bilge for Deck Steped Mast

Looking to hear what the internet community thinks about this one.

The surveyors noted about a 1/4" of rot at the base of the compression post. Meaning they were able to stick an ice pick 1/4" of an inch into the wood. I want to replace it. Keep it simple and use the same material that is in there, wood. Treat it with water tight paint, glass it in. Want to keep the price on this fix low, but do it properly. I have read about others replacing with steel or aluminum. Looks great, but wood was the original idea when the boat was built, so I will replace it the same way. Maybe down the road when I have extra cash, I will mock it up in CAD and have it made out of machined aluminum.

Question is: Can I use a bottle jack to jack the mast up enough ~1mm to remove old wood (and glass/junk, refer to image #1) and replace with new post without demasting?

Recently bought a boat. 1979 Cal 31'. Excellent condition, clean throughout, all records and well kept by the previous owners. But being a 36 year old boat, there are a few problems. We had a survey completed and they gave us some suggestions on things to repair. Due to some of the suggestions, the insurance company is suspicious and requires being fixed before being completely insured.

The compression post is located in the bilge and creates a foundation for the deck stepped mast so that the mast doesn't compress into the boat. Also going to note that a survey was completed back in 2009 and seems to have missed this detail. And to clear this up as well, the location where the mast sits on the deck, has no signs of rot, damage, cracking, or sinking. The boat sails great and performs well in the Southeast Alaskan waters.

I would like to replace this with new 4x4 treated and coated block of hard wood and glass it in (similar to image #2 (found from a blog)). Looking at the picture, I believe the first owner (owned since new 1979-2009) must have replaced this a few years back. It appears to have glass, epoxy, or a hard compound at the base going half way up the wood. It simply looks like a quick-fix with a pile of mud and junk at the base.

So, do I have to demast? After removing all the junk and debris next to the post, can I simply use a bottle jack behind the post, jack enough room (~1mm (making sure to not cause more damage)), remove block, clean out, and replace with new?




Thank you, and I appreciate the suggestions.

Rob
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Old 13-05-2015, 15:57   #2
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

I would say it probably was a factory job but can't be certain. If glassed in place with no place for moisture to go it will sit in bilge water until it rots again. If you choose to redo with 4x4 (perfectly acceptable) then dip the bottom end in penetrating epoxy a few times before placing it in the bilge and make certain there is a way for moisture to escape around the base of the 4x4.

A hydraulic jack will move your cabin top and mast up as far as you want as long as you take tension off the shrouds and stays. Be careful. It could take loose your tabbing for bulkheads if it goes too high. Make certain the pressure from the jack is close to the build up of the cabin top very close to directly below the mast step or position a cross beam with a hydraulic jack on each end. Take care and be safe.
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Old 13-05-2015, 17:14   #3
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

That 36 year old boat should have the rigging replaced anyway.
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Old 13-05-2015, 19:06   #4
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

Just take tension off the shrouds and stays using your turnbuckles. Don't release them. I saw an Ericson owner release all his rigging before the crane hooked up to his mast. That was a hard lesson.
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Old 14-05-2015, 05:38   #5
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

Greetings and welcome aboard the CF, Rob.
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Old 14-05-2015, 12:09   #6
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

I have a 36 year old 38' ketch and while the previous owner went cheap on almost everything he replaced in his 20 year ownership, he or someone did replace the post support located in the bilge with a piece of properly sized PVC pipe; about 6" round. I thought it was clever as it would be easy to fill with non shrink something and it's completely impervious to water and oil and age.
You might want to rethink the loyalty to wood as your boat appears to be fiberglass and that's for a reason. The boat won't mind the upgrade.
"that was a hard lesson.." the master of understatement re someone taking off his rigging before the crane hooked up.
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Old 14-05-2015, 12:12   #7
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

PVC pipe is completely inappropriate for use as a compression post.
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Old 14-05-2015, 13:02   #8
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

It might be unorthodox but it's been there for years as have all the underground sprinklers in the state of Florida. On end thick wall PVC is not compressible and I'd take it over wood in the bilge any day.
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Old 14-05-2015, 13:07   #9
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

As I said, it is completely inappropriate for this use, as it does not have the necessary compressive strength and especially because it cold flows.

Yours might have "been there for years", but it is now measurably shorter than when it was first installed.
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Old 14-05-2015, 17:08   #10
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

How are you going to jack it up and then work around the bottle jack in that tight space?

I would think this would be a good time to step the mast, and might as well update your rigging at the same time. If your tangs are in that kind of shape it would be good to know.
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Old 14-05-2015, 21:01   #11
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

Here's a link to a solution that took less than a day... no snake oil!


The 60 minute compression post - SailboatOwners.com=
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Old 14-05-2015, 21:10   #12
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

An H-beam is a mildly poor choice because it is heavier than needs to be, as it is designed for bending loads.
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Old 15-05-2015, 23:20   #13
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

Nova, It's aluminum.
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Old 16-05-2015, 02:27   #14
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Re: Compression Post Replacement in Bilge for Deck Steped Mast

Sea--if you mean that your compression post is aluminum, not PVC, that's a good thing.
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