Crack in the Compression post. - SailNet Community

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  #1  
Old 01-17-2010
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Crack in the Compression post.

Greetings all,
I live aboard a 38' Downeast Cutter that I purchased back in Sept 2009. Yesterday, I noticed a small crack not even wide enough to stick a butter knife in running the length of the compression post, which is a 4"X6" piece of oak (I think). Under the cabin sole, it looks to be epoxied into the forward bilge. Obviously at the marina, I hear a million different ideas on how to fix this, including to not fix it (keep an eye on it approach that I am not fond of), to run some bolts through it to prevent it from getting worse, or replacing the compression post entirely. What are your thoughts/suggestions?
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Old 01-17-2010
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Hi, Welcome to Sailnet!

It's hard to give an opinion without seeing some photos (even then, it's not the same as inspecting in person). You'd have to build up your post-count to 10 before you can put up photos here, but that's easily done by adding some gibberish over in the Song Thread.

Instructions for how to post photos can be found here.

If you are able to show us some photos, try to have a ruler or some other measurement in the photo so we get an idea of scale.
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Old 01-17-2010
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I would highly recommend replacing the compression post with one made of either stainless steel or aluminum, preferably stainless steel. One thing to check for ASAP is whether the deck is dishing at all at the point the mast is stepped. If so, it might indicate that the compression post has compressed or weakened already. If this is the case, you would probably be wise to unstep the mast and do this sooner, rather than later, as if the compression post fails, it will be rather dramatic...

Ideally, the new compression post would be bolted to a step in the bilge that transfers the load to the keelson and over a substantial portion of the hull via a stress grid or some stringers and floors. The top of the compression post should through-bolt to the mast step on the deck.
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Old 01-17-2010
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You need to determine whether it is indeed a crack or whether it is a "check". Larger pieces of wood will naturally develop checks and they are nothing to worry about. I remember the first time I saw the checks in the 80' mast of a schooner and was convinced that the rig would come down when of course everything was perfectly normal.

I would suggest watching the crack while sailing and see if it opens more. If it does when you are sailing hard, then you should do something about it.

If there is in fact a problem, it would be wise to figure out why. It could be that the compression post is simply not large enough. It could also be that it has started to rot(if you try to pull a little bit of wood out from the crack, what does it look like?)

As for repair options, you have a couple. The post will still be just as strong in compression except that it will be more likely to buckle so it is buckling that you need to prevent. In addition, you need to worry about rot since there might already be some or your repair could trap water and cause it. Given the size of the crack, packing it full of epoxy will be quite difficult. The problem with running bolts through it is that you create stress concentrations. Another option is to fabricate a collar that goes around it and clamps it together. As long as the post was big enough to start with, it can take the compression so you just need to hold it together. You don't even need to hold it together along the whole length, buckling is proportional to the square of the unsupported distance so just attaching it at the middle will make a big difference.

From your description, I am not even sure there is a problem. Someone who actually understands wood can help you with whether it was caused by stress or whether it is natural.
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Old 01-17-2010
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IMHO a 4x6in piece of Oak is going to have much more compression strength than you could possibly exceed with that size boat/rig.
It is most likely due to shrinking and I would not do anything with it.
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Old 01-17-2010
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Without seeing it, it's hard to be definitive but I think Kaluvic has it right.
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Old 11-28-2011
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I replace mine with teak, however the main reason i did this is that I was mad at myself for cracking it when I reinstalled the lag bolt before stepping the mast. The mistake I made was putting sealing compound in the lag bolt hole in the top of the mast. When I screwed the lag bolt back in the hole it created hydraulic pressure and pushed the top of the compression post open. In some places the lag bolt hole is only about 3/4 " away from the edge of the compression post. I had spent so much time fixing up the boat I did not want to put it back together with this unhappy occurrence. I found some teak and had it milled to shape so that the bulkhead fit into the slot and the cabin door closes properly. Best of all, no crack, and I can sit and admire it any time I like. It's really up to you if you want to fix it. If it is not opening, moving, flexing, groaning etc, it is probably nothing to worry about. There is probably other stuff to worry about that you don't know about yet .. Hope that helps.
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Old 11-29-2011
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Red Oak, the most common, is prone to cracks. Try white oak. Teak? http://www.ibiblio.org/twa/info/lumberSelection.pdf

For technical info: Species Guide
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Old 11-29-2011
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Greetings Earthlings ! If it's not structually deficent and it's only cossmetic you can use the age old way of extra stregth learn to wipp and do loads of turks heads and other fancy rope working and that will keep it all together then epoxy the lot, too keep it clean and strong GO SAFE
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