Compresion post repaired - SailNet Community

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Go Back   SailNet Community > Boat Builders Row > Islander
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  #1  
Old 12-17-2008
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sailho is on a distinguished road
Compresion post repaired

Finally finished the compresion post repair. Took the better part of a day. I loosened the turn buckles, and jacked the mast up.The compresion post came out of the floor easily (no rot at all). I epoxied two aluminum plates under it like a pyramid. Very clean and works well. I appreciate all the advise given.
Sailho
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Old 10-30-2009
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I am close to purchasing 78 Islander 28. My surveyor found rotting plywood in the bilge at the lower end of the baffles that become structure for the floor and one which the mast compression post bears on. Have you found similar issues in your boats? My surveyor thought it wasn't super major b/c there was plenty of solid wood where it was needed, but it needs to be fixed. The owner offered to make it right and cut out the rotting wood and glass in new.

Have any insights or thoughts?

Thanks!
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Old 10-13-2011
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I am a new owner of a 1978 Islander 28 and have a compression post issue as well. The other threads indicate removing the existing post and replacing/shimming the bottom end to restore the correct height. Looking in the head, there appears to be a post in the corner of the bulkhead and inner cabin wall. Is that what has to be removed? When lifting the floor bilge boards I can see a plywood plate on top of the stringers but do not see any distortion or collapsing. The oak shelf above the table has cracked and distorted due to the compression loads and I would like to restore it if not too difficult. Any suggestions?
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Old 10-14-2011
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I changed out the plywood with 3/4" of AL plate. The material needs to be large enough to cover both of the floors which are (basically) located under the compression post built in to the corner of the head enclosure. I built the plate wide enough to spread the load to within a few inches of the hull. Not to close, you don't want to build in hard points....

I had the cabin sole out from the middle of the head door aft to the companionway steps to permit other repairs so I had full access. If you carefully cut the sole out aft of the head, about a foot, you should have enough room to do a similar repair and then cut to fit and reinstall the original plywood.

One change I would make is provide either a slick bearing surface for the post to "work" on of perhaps add provisions to shim the bottom of the post. Under a hard sail the bulkhead sometimes growls as the boat hull flexes under load. Need pictures?
Paul Comte
Milwaukee, WI
Islander 28
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Old 10-14-2011
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Thanks for the prompt response. I can see a piece of ply across 2 stringers which I am assuming is the plywood to be replaced. How is the post attached to the bulkhead between the cabin and the head itself? I would assume the lightening ground runs through the post?


Pics would be great as thery are usually worth a thousand words (or so).
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Old 10-15-2011
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Well "Sundayflyer32", I don't know why those other folks are ripping that post assembly apart. Unless the post is rotten, I can't see any reason to replace it. (even if split I'd install carriage bolts through it...) Also, I can't see how replacing it will address the source of the problem, i.e., the poorly supported, under-strength, doomed to be crushed plywood cabin sole.

BTW, that is not Bob Perry's problem but is Islander's engineering interpretation of his design.

Paul Comte
Milwaukee, WI
Islander 28

PS, On our boat, the Ground cable and mast electrical leads run down the starboard side of the post covered by a piece of wood trim. pc
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Old 10-23-2011
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Paul Comte pretty much nailed it. The problem results from placing two pieces of plywood under compression. As most of us understand, resisting compression isn't something plywood is supposed to do, especially in a damp environment. Apparently the engineers who actually built the boat didn't know or didn't care. Because of deck leaks around the mast, our '79 Islander 28 had both the 3/4" plywood sole and the 3/4" plywood countertop rot and collapse which resulted in the mast dropping well over 1". The wooden post you mention is firmly attached to the bulkhead so unless it is rotted I would leave it alone. When you jack up the mast, gaps will appear above and below the wooden post as the weight comes off and you can chisel out the old plywood. Replacing the teak veneer countertop was a major proposition which involved removing all those beautiful teak plugs covering the wood screws on the counter rail, jacking up the mast and pulling out the remains of the countertop to use as a template. When we replaced the countertop, we left a circular hole in it the size of the bottom of the steel compression post and cut an aluminum disk to fit between the steel post and the wooden post that you see in the head. Be sure to leave a slot in the disk for the mast wiring. On the bottom, we cut away the sole and placed more aluminum plates bridging the two stringers in the bilge. Because we were replacing 3/4" plywood we backfilled with 3/4" aluminum sheet stock. If you are going to replace the countertop, I would also recommend treating the sole as well even if it doesn't look bad right now. You don't ever want to tear things up again. We did all this in our marina berth with the mast stepped using a 2 ton hydraulic jack but it requires nerves of steel to listen to all the cracking and creaking as the mast comes up. My wife had to leave - I had to have a ration of grog. It would be much easier to do it on the hard with the mast removed. Sorry for the long reply. I suppose I should have just sent some pictures. Please let me know if you have any other questions.
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Old 10-23-2011
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"and cut an aluminum disk to fit between the steel post and the wooden post that you see in the head. "
Aluminum plate, or unknown alloy, next to steel? If you don't insulate the two (i.e. put in a piece of UHDPE) you are likely to get galvanic corrosion there in a mainre environment.

I've seen Bob Perry's drawings for the I28 and they show several differences from the production boat. One of them is what appears to be a sensible keel-stepped mast instead of the offset kludge that actually got built. But, of course, if they'd built it with a simple mast they couldn't have shown the pictures of the "huge" open interior, which probably sold more boats for them than anyone asking about how well plywood would age. But at least for the deck and cabin top core, they did use Bruneel plywood, which ages like iron.
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Old 10-24-2011
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Thanks "Hellosailor". You are absolutely correct about the need to isolate two dissimilar metals and anyone else unfortunate enough to attempt this repair should heed your good advice. Even more galling is the fact that I had a sheet of UHDPE laying around at the time. On the other hand, here's how I can avoid not sitting bolt upright in the middle of the night in a cold sweat and immediately jacking up the mast to insert said dielectric material. As you know, the rate of galvanic corrosion is dependant upon the amount moisture and the duration of it's presence. Obviousy, the more moisture for a longer period, the better the "battery" so to speak. What caused my problem in the first place was a leaky deck around the mast which I hope I have a least slowed down. "Dry" is impossible on a boat for a lot of reasons but at least water no longer constantly drips onto the counter and compression post. I have achieved "pretty dry" in that area. So although galvanic corrosion is doubtless occuring even through the thick layers of factory black paint on the steel compression post, it's the rate of corrosion I'm considering late at night. At the magical age of 64, I'm willing to bet that my personal rate of decline (and probably that of my 30-something boat) will exceed that of my repaired compression post. Thanks again for your astute observation.
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Old 10-24-2011
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Re: water intrusion from deck stepped mast. I made a plastic (cheap cutting board) template to locate the wire location under the mast. Use the bolts as an index. Then after removing the mast step casting, I cut an opening around the mast wires at the cabin top. I slid a sleeve of bicycle inner tube over the wires and then a threaded bronze nipple over that. (use the largest one you can make fit) I made gummy ball of thickened epoxy to plug the bottom of the hole I'd carved in the cabin top and then filled in around the threaded part of the nipple with a more wet thicked epoxy mix. The template comes into play locating the nipple so the mast step casting is not interfered with... I have a piece of hose over the wires and onto the nipple. The hose is folded inside the mast so water cannot enter the boat in this area - period! I didn't need the nipple and a thinner stainless tube could work as well - but I had the nipple already...

The following year I addressed the dimple which had been driven into the cabin top by the previously unsupported mast loads. I floated a mast step turning plate on a bed of thickened epoxy (used nylon washers to shim it properly, a dab of five minute epoxy would hold them in place.) The trick there was to make sure the step wound up perpendicular to the where the mast should point... You get one easy chance at this so get those shims glued and mask the area around plate on the cabin top (doing it again, I might use a bead of silicone caulk as a dam to control the epoxy flow.) I've got a dry boat, and with the plate and turning blocks, am taking more loads and leaks off of the cabin top...
Paul Comte
Milwaukee Wi
Islander 28
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