Proceedures for core repair from below decks

[jhenson]

The weather here in Virginia is just about to get warm enough for me to start the core repair on my Tartan 34c. I have the boat now under shelter, and am beginning to remove the necessary deck hardware. Of particular concern to me is the area beneath the cockpit seats and sole. This area is, by far, going to be the most difficult section for me.

In 1989, the boat was returned to the Tartan factory for a major $35,000 refit. There were isolated areas of the deck re-cored, some of which are now in need of repair. The cockpit sole and areas of the cockpit seats were also in need of core work. It appears that rather than replace the core in these areas, a teak cockpit was placed over these areas. Essentially, the cockpit horizontal surfaces have ½ inch marine ply overlaid with teak strips. The plywood is glued to the upper skins of the cockpit seats and sole. For some reason, the sole has bolts that penetrate the original surface. The bolts are covered with large bungs above, but leak from water passing through the seams. The caulking does need to be replaced in the entire cockpit. Also, complicating the option of just scrapping the teak, the three locker lids are not the original fiberglass versions. Instead, they are entirely marine plywood, and teak overlay. The teak and plywood are in good shape thoughout the entire cockpit, including the locker lids.

The core over the quarterberth , which is also the core under the port cockpit seat is very wet. Water condenses on the overhead during cold weather. Also, the dripping under the cockpit sole, while not a lot of water, is annoying and keeps the area adjoining the quarterberth very damp. Tartan did not fit a bulkhead separating the area below the cockpit sole and the quarterberth, but I intend to do so.

After some experimentation, I’ve come to the conclusion that removal and salvage of the teak and plywood is just not possible. That leaves only a couple of options:

-removal of the entire teak and plywood , and repair of the core from above. New lockers will have to be constructed to accommodate the change in the deck thickness, or new teak and plywood applied.

-attempt the replacement of deck core from below with some way of isolating any though fasteners that are there now.

Before I trash the teak and plywood, I’d like to explore the idea of replacing the core from below. Never having done this from below, I’m approaching this area with a great sense of dread. How does one apply material like 17 oz. biax cloth upside down? I’ve applied small sections of biax tape before when the epoxy was “tacky” enough to hold the weight of the material. This seems much more challenging. If the skins are reused , what form of clamping method works best? Any insights, thoughts, or recommendations into this are greatly appreciated.

Thanks!

Joe

[Case]

I recall one website which the owner of a Pearson 26 replaced his core from under the cockpit. I'll have to look for the website, it was a good one.

Basically, what he did was to remove the core from underneath. Cleaned up everything then cut the balsa to shape, glassed one side (before putting on the boat). When it was done curing, he then used plywood to support the balsa and jacked it up into place. He then fiberglassed the edges. Once everything cured, he just backed off the jacks and that's it.

This sort of repair is not heard about that much because most recores involves the decks which is not... conveniently square or rectangular and flat...

- Case

[David]

Joe,

Maybe I am missing something in your post, but it seems to me if the caulking for the teak sole and seats needs to be redone and is leaking, wouldn't the plywood substrate be damaged by water as well. Surely all the water that is saturating the core is getting to the core thru the plywood.... (I would hate to think of you recoring from underneath in order to save the teak only to find you still need to rip up the teak later to replaceace the plywood.

David

[barrybrown]

I recently replaced some of the coring on my Triton foredeck from inside, it was not that difficult and I liked the result.
I cut the inner skin with a grinder (maybe the worst part of the job) and saved the pieces. It is necessary to leave enough of the inner skin on the edges in order to tape the cut out back in place. If there is moisture under these edges make a tool to rake the coring out and replace this coring before replacing the cut out piece.
Next clean both surfaces, cut the new coring to the size of the cutout skin, set the coring and skin in place (dry) and cut some support sticks, enough to firmly hold it in place.
Next wet out all surfaces except the upper surface of the coring, mix some thickened epoxy and spread it on the cut out skin, lay the coring on on the skin, wet out the top of the coring then spread it with thickened epoxy.
Put the piece back in place and support with the sticks cut earlier.
Next mix some thickened epoxy and fill the gap around the edges of the panel.
After it has set grind a bevel on each side of the cut lines and tape these seams.
In my situation I replaced balsa with balsa of the same thickness and the interior sections matched evenly.
Barry

[jhenson]

David,

That's a good question, to be sure. I've removed caulk in multiple areas, and the plywood is firm everywhere I have tested. Yes, it is wet in a few areas, but I can't detect any soft spots with a screw driver. I can also see along the edges of the plywood by removing the side pieces, and there are no edges that are delaminated. Does the fact that marine plywood is wet and passing water around some fasteners imply that it is nearing structural failure? I know we utilize marine plywood on boats with idea that it may be wet at some point, though that's certainly less than ideal.

Maybe I am barking up the wrong tree here!

Joe

[Ronin120]

Years ago I replaced 3/4's of the plywood core in my Cal 25 and confronted the same problem. I pretty much did what Case was referring to, I made templates of the areas to be re-cored, cut them out in my garage, prepped them ahead of time with fiberglass cloth and epoxy, leaving some of the cloth hanging off the edges for wetting out later.

After removing the old core (the hardest part of the job) and cleaning and prepping the surface, I just mixed up very thick consistency epoxy and applied it with a serrated trowel. Before doing the job I dry-fit the panels, propping them in place with a goodly number of 2x4's cut to spec. I also placed trashcans all over the deck ahead of time. With the epoxy in place I just fit them up, put the panels in place, chocked them up and then filled the trashcans with water to apply pressure.

Came back after the epoxy had set and finished off the filleting and tabbing.

Not terribly professional but it worked well.

Best

[David]

Joe:

<<Does the fact that marine plywood is wet and passing water around some fasteners imply that it is nearing structural failure? >>

My concern would be that the plywood is allowing water to pass thru it, thru fastener holes perhaps, thru fittings in the sole like the cockpit drains, the pedestal steering and brace, or the sole plate for the rudder post, etc. The integrity of marine ply is in the glue not failing from water saturation. It is still wood and can hold water just as coring can. From your description it sounds like you have a LOT of water in your core, which would mean its getting in from more than one little screw hole.

I take it the idea of recoring from underneath is to save the teak if possible? If you seal the top skin of the sole and seats from underneath from all screw penetrations, and you can dry out the plywood, and you can recaulk the seams to keep the plywood dry in the future, it seems to me that would give you a very nice teak laid cockpit. But otherwise you may just be moving saturation up from the balsa core to the plywood substrate.



David

[jhenson]

I take it the idea of recoring from underneath is to save the teak if possible?

Yes, it is.

If you seal the top skin of the sole and seats from underneath from all screw penetrations, and you can dry out the plywood, and you can recaulk the seams to keep the plywood dry in the future, it seems to me that would give you a very nice teak laid cockpit.

Those are exactly my thoughts, though the proceedures for doing so I have yet to figure out, and would be tricky. If the screws do penetrate the original deck (I don't know yet), I thought I might just grind them off flush with the underside of the deck, since they obviously provide little purchase in wet core. I would then hollow out the core material (not balsa here) below the screws and fill these indentations in the core material with thickend epoxy just before raising it into position. That way the screws would hopefully be isolated from future leakage into the core. The through bolts in the sole are a bit trickier, and I have no idea yet on them, though I'm thinking that I would be better served not having teak on the sole, and opting for a grate instead.

Maybe this is more trouble than it is worth.

Joe

[David]

Joe,

Is the teak screwed down in a traditional method, or epoxied in place without screws? If screwed down, I would consider removing the bungs, removing the screws, filling the thread hole with epoxy and epoxying a new bung in the hole. My guess is that if the teak is screwed down, the yard screwed thru the ply and into the original core as well, which may be part of your problem...

<<If the screws do penetrate the original deck>>

Each place they penetrate the original deck they are also penetrating the plywood and potentially leaking into the plywood as well. IOW, you could grind them flush to the underneath side of the cockpit sole skin, but they still may be leaking above that into the ply.

The thrubolts could simply be overbored and filled after the recoring is done, thru the teak, thru the top skin, thru the new core but not thru the bottom skin.

David

[mitiempo]

in my opinion, and that of others, you can recore from below with some difficulty and ingenuity, but you can't repair leaks from below. To repair the leaks into the core you will have to access all possibly leaking fasteners and you won't know which ones without removing the teak. If you could remove all the core from below and replace with glass and no core it might work, but you would still have to rebed all fasteners from above. I think the whole job would be easier and faster if all wood was removed carefully and done from above.

[Hirilondë]

Joe,

Is the teak screwed down in a traditional method, or epoxied in place without screws? If screwed down, I would consider removing the bungs, removing the screws, filling the thread hole with epoxy and epoxying a new bung in the hole. My guess is that if the teak is screwed down, the yard screwed thru the ply and into the original core as well, which may be part of your problem...

Yup, and if so all your recore work and any hardware rebedding goes to waste. One disadvantage to recoring from below, in your case at least, is that you may not know the cause of your water penetration until it ruins all your work. If this is part of the problem, David's solution may not solve it either. Relying on bungs to waterproof teak decking is looking for trouble. If they didn't bed the teak really well, thus sealing the screws as the teak was installed, they blew it. Teak decking is supposed to be like a non-skid surface. It shouldn't be why the deck doesn't leak.

You may really need to tear that all up too. There are just too many unknowns here. No good way to know if the problem is isolated or whether one problem was simply applied over another. I hate to be the pessimist, but recoring in itself is a ton of work. To risk it to save a questionable teak covering is a scary prospect to me.

If in your surgery you can prove just what is leaking my warning might be null and void. I would sure want to know what the problem is, and that it was resolved before finishing the recore.

[Case]

Personally, I would remove all bungs and unscrew all screws. Then remove all of the soft core from underneath the cockpit floor.

Once the epoxy hardens, proceed with the new core underneath (fiberglassing one side beforehand) then jack it up into place (epoxy already lathered on the top of the core). Then fiberglass the edges.

Once everything has cured, I then would drill thru the bung holes from above then fill with thickened epoxy. Once the epoxy hardens, drill again and screw in the plywood into solid epoxy.

This way, the new core will never be bothered forever. Of course, therin lies the one little problem... the wet plywood.

Still, sometimes you have to put off something and just go sailing. Replace the wet plywood in the future. Is it wet but still solid? Then you could put it off for a few years.

In a way, life is all about controlled deterioration...

- Case

[bcooke]

I am not saying recoring from underneath is the way to go in this case but to answer the question about recoring from below.

1.) I hate laying in skins from underneath.

2.) I have used the board method. That is, a board (covered in wax paper or something more professional) to support the saturated glass while the epoxy kicks. It works okay for small sections but I wasn't crazy with the quality. Good enough for my application but not stellar results.

3.) I have been thinking about vacuum bagging. Its easy, and I would think the results would be better than just laying it up or using a board.

I think if I invested in a vacuum bag setup I would probably use it quite a bit actually.

Didn't you just get rid of a project boat?

[Tim]

You've received plenty of good comments here, so the only thing I will add is that I can't imagine a scenario where I would even contemplate reusing the old inner (bottom) skin from most cored laminates. (For that matter, I also have determined for my own purposes that reusing topskins is sort of a false economy, but that's another subject.)

I'd plan on using new fiberglass to cover your core. I think it would be easier and better to use new material, and is quicker to boot. It also makes for a better overall job.

Remember that you can use smaller pieces of fiberglass to make the process easier--you don't need to try and install, say, a 2x3' piece all at once. There is nothing wrong with using manageable pieces, and staggering the joints between layers. This makes working overhead much easier.

Are you planning on working on your Tartan for this entire year, without any plans to get her in the water? You may have said this in your initial posts when you bought the boat, but I can't recall. If so, then attack this core.

If you hope to get in the water this year, and depending on the severity of this cockpit problem, I'd consider waiting on this repair. I second what others have said about ensuring that you properly locate and repair all related problems and don't jump prematurely into repair of one thing only to find that the root cause is still an issue. Repair it correctly when you do, but if time is critical (i.e. launch date) and the problem can wait a little, then let it wait and plan for the real job after the season. It sounds like there are enough question marks about the whole cockpit/teak/locker construction that the way forward is not yet quite clear.

[Case]

I don't think my explanations were clear enough. So I finally found the website with the the core repairs done from underneath.

This only really works with flat surfaces.

The website with under cockpit sole recore.

- Case

[jhenson]

Thanks everyone!

That gives me a lot to think about. I’m probably not going to attack this issue from below decks after considering all the good advice here. What form of repair I will take here, I still don’t know.

The plan for the boat is to have it at my home for all of this year, and launch in the spring of 2010. The primary goal is to have her decks solid, repainted, and work on some rigging issues. If I can get her topsides repainted, so much the better.

Joe

[Quetzalsailor]

A friend of mine recored his dad's 'big' boats foredeck from underneath. Now, he had access to an experienced, equipped shop so he made up a core and bottom lamina prefabbed panel, cleared the underside of the upper laminate of the deck and vacuum bagged it together.

Question more to the sages on this list, than advice from me but: If you pull this thing apart and find it peppered with screws, like a Choey Lee, can you not grind the screws flush, glass and seal the whole under surface of the upper lamina before laminating the new core and the new lower lamina? That would solve the ongoing leak problem from the teak assembly fastenings, and would leave the inevitable future replacement of the teak no more difficult than ever.

I listened to my friend's report of fixing his dad's boat and could not understand how he could be sure that he'd gotten a good tight bond over the many square feet of foredeck (surely both the deck and the repair panel had stiffness). I've done a similar repair under a cockpit floor and relied on filled epoxy and prop sticks, successfully, but a much smaller problem.

[mitiempo]

In the case of a teak over glass deck full of screws, I would be worried about the screws getting hot when ground off I think. This, if it happens, would loosen the screws because of the heat and if it happened a lot I think the teak would not be as well attached as before. I guess it depends on the thickness of the upper laminate. Just my opinion.

[Quetzalsailor]

Good point. Been there, but with a far fewer collection of screws.

If you're talking about an 8th of an inch, or the tip, it grinds quickly with your 4 1/4" angle grinder, and without much cooking. If the whole of the screw dia protrudes than it'd be quicker and cooler to whack it off with clippers or a Dremel, depending upon the dia and your stamina. The Dremel cutoff wheel that I have in mind is about 1-1/4"dia and 1/32" thick so not much metal is being ground. Amazingly useful tool for such a toy-like thing! I'll use it before I grab a hacksaw for even 1/2" stainless bolts, faster and only minor burrs to clean up.