# Wet plywood deck core - how to dry?



## laHolland (May 22, 2009)

We noticed that there was some coffee-like liquid oozing from a seam on our Cal 27's cabin ceiling. So we knew we had a soggy deck, though it doesn't feel spongy when walking on. The boat cabin isn't lined, and there isn't any paneling or furniture in the way, so it is easy to access the deck from the interior. We cut out a small section with a dremel tool, without going through to the top. The construction of the deck is, from the top to bottom, gel coat, fiberglass layers, plywood, fiberglass layers. The small section we removed revealed that the plywood was damp but does not appear to be rotten or mushy. The plywood was still attached firmly to itself and both layers of fiberglass. So my problem is -- how to effectively dry out this plywood? The area that needs to be dried is large - I think the moisture wicked along the wood grain, from a leaking chainplate nearly back to the companionway. I expected the plywood to be rotten, but it is quite firm and we really had to pry/chisel it off, though it is clearly damp.

So, I am thinking we can pry/peel away the inside fiberglass layer, and attempt to dry the plywood from underneath using a heater, but I don't know if this will work, as the water vapor cannot escape upwards without putting holes in the deck surface (which I'd rather not do).

Anyone had any experience with this, or any ideas?


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## sailingdog (Mar 19, 2006)

I don't think you're going to really effectively dry out that plywood in any reasonable period of time. It has probably taken a long time to get this wet, and would take a really long time to dry, especially with only one side exposed. IMHO, you'd be better off re-coring the cabintop. Marine plywood is the worst of all core materials for cored laminates, as you can read about *HERE*.

If you do decide to recore the deck, it would be my recommendation to cut the top laminate layer away rather than try and do the work from the underside. Working from the top will make the repair go much faster and gravity will be working with you.

Working from underneath will require you to mask off the entire interior and will make it much more difficult to get a good layup without voids. Finally, any bulkheads are going to make getting the core repair more difficult to do.

Finally, I'd recommend using end-grain balsa or a ductile polyurethane foam like Divinylcell. While a rigid foam might be better, it would be harder to work with. For end-grain balsa, something like ContourKore, which is designed to allow the material to follow fairly complex curves, rather than solid sheets of it, would make laying up the new core much easier.

You should probably plan to make the areas beneath major hardware solid laminate, rather than cored laminate, and any smaller hardware that is mounted through the cored areas of the deck should have the fastener holes potted. To do this properly follow Maine Sail's excellent *directions*.

I'd also recommend you read my *article on marine sealants* prior to rebedding any deck hardware. One of the most versatile and effective sealants is Butyl Rubber Tape, which you can get at many glass repair shops. Not only is it very useful for bedding all kinds of deck hardware, it is also very inexpensive compared to other marine sealants. However, I would not recommend it for below-waterline use.



laHolland said:


> We noticed that there was some coffee-like liquid oozing from a seam on our Cal 27's cabin ceiling. So we knew we had a soggy deck, though it doesn't feel spongy when walking on. The boat cabin isn't lined, and there isn't any paneling or furniture in the way, so it is easy to access the deck from the interior. We cut out a small section with a dremel tool, without going through to the top. The construction of the deck is, from the top to bottom, gel coat, fiberglass layers, plywood, fiberglass layers. The small section we removed revealed that the plywood was damp but does not appear to be rotten or mushy. The plywood was still attached firmly to itself and both layers of fiberglass. So my problem is -- how to effectively dry out this plywood? The area that needs to be dried is large - I think the moisture wicked along the wood grain, from a leaking chainplate nearly back to the companionway. I expected the plywood to be rotten, but it is quite firm and we really had to pry/chisel it off, though it is clearly damp.
> 
> So, I am thinking we can pry/peel away the inside fiberglass layer, and attempt to dry the plywood from underneath using a heater, but I don't know if this will work, as the water vapor cannot escape upwards without putting holes in the deck surface (which I'd rather not do).
> 
> Anyone had any experience with this, or any ideas?


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## laHolland (May 22, 2009)

Thank you for your insights. We will only be repairing the port side of the boat - the other side is dry and solid. Would it be bad to replace one side of the boat with a different core material than the other half? 

Also, our cabin interior is currently undergoing a rehaul (read, it's a complete mess), and we were planning on redoing the interior ceiling anyway (peeling paint, stains, sharp, poorly laid fiberglass surface, very yucky), so it's much more appealing doing the work from the inside, especially since one of the few unblemished parts of our boat is the deck. Also, there's the weather issue. In your opinion, is it completely impossible to do a halfway decent job from the under side? I say "decent" - I don't expect perfection.


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## sailingdog (Mar 19, 2006)

It isn't ideal to have the two halves of the boat cored with different materials. However, it isn't a complete deal breaker IMHO. However, doing the work from the underside is going to take a lot longer and it is a lot harder to get it right. If you brace the layers properly, you can probably do a decent job of it. Using vacuum bagging would help, but that may be more complex than you want to get into.

One person I know who did this on two different boats said that doing it from the underside took about four-to-five times as long and that isn't counting the clean up, which was a lot more laborious as well. The repairs were about the same size IIRC.

If you do decide to do this, I would highly recommend using epoxy from Progressive Epo_xy Polymers and Resins in NH and getting your fiberglass from www.fiberglasssite.com. Remove everything from the cabin that you can and tape a heavy plastic tarp over the interior.

I also recommend using a full-face respirator mask with vapor and particulate filters rather than goggles and a half mask. *DO NOT USE THE DISPOSABLE MASKS-they are worthless.* The full-face mask respirator will last a long time if you care for it properly and is far more comfortable than the half-mask and goggles.


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## NICHOLSON58 (Feb 22, 2009)

There is another option for core material I am using to rebuild my rudder. The original with three SS ribs and foam core with glass and Kevlar skin was totally waterloged. I built up inner structures and then filled with syntactic foam. The mix I used was 3 gallons of low viscocity Epoxy resin and 7 gallons of 3-M micro-balloons. The bleded gooy mass is like warm Kraft Marshmellow creme. Cured, it is supposed to have a compressive strength of 3000 psi. The resin is no-blush 635 from US Composites. (they also sell the balloons and cloth) The "foam" can be easily sanded and shaped. The finished skin will be graphite & vacuum bagged. My intent is to have a truely water-proof structure.

You might consider using this system to form your core in situ if you can leave the insided glass layer in place. (make gravity your friend). I have also found that you can form the stuff if you put down the foam and apply a release film. If need be, you can also press the film to hold it in place by using cardboard forms and props. You should get excellent bonding to this material as you build up the top layers. I suggest you try a few resin & balloon ratios to decide what will work best for you.


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## davidpm (Oct 22, 2007)

sailingdog said:


> I also recommend using a full-face respirator mask with vapor and particulate filters rather than goggles and a half mask. *DO NOT USE THE DISPOSABLE MASKS-they are worthless.* The full-face mask respirator will last a long time if you care for it properly and is far more comfortable than the half-mask and goggles.


SD
Do you have a link to a mask you have in mind? Also do they work with paint products like AllGrip too?


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## davidpm (Oct 22, 2007)

NICHOLSON58 said:


> I built up inner structures and then filled with syntactic foam. The mix I used was 3 gallons of low viscocity Epoxy resin and 7 gallons of 3-M micro-balloons. The bleded gooy mass is like warm Kraft Marshmellow creme. Cured, it is supposed to have a compressive strength of 3000 psi. The resin is no-blush 635 from US Composites. (they also sell the balloons and cloth) The "foam" can be easily sanded and shaped. The finished skin will be graphite & vacuum bagged. My intent is to have a truely water-proof structure.


Do you have a link or part number for your micro-balloons. I didn't see it on the site. Also where did you find the 3000 psi number


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## ROSA (Oct 22, 2009)

If the area is not too too large and the plywood is still in good shape I would remove the interior skin and place a dehumidifier inside, seal up the cabin, and let it run for two weeks or so. They work better than a heater and you may find that the removal of the wood is not necessary at all, assuming that it is still well attached to the outer skin.

A friend was able to dry out the interior of his West sail 32 in this manner and found everything in good shape and ready for re-finish. It is certainly worth a try before you really know if a re-core is necessary. He also discovered in this process that he had termites, due to the wet wood. They, the termites, dried up like grains of rice and covered all flat surfaces.


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## laHolland (May 22, 2009)

That's a good idea, Rosa. I think I will try that first, and then reevaluate.


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## sailingdog (Mar 19, 2006)

The 3M series 6000 full face mask respirator is the one I use.

See *HERE.*

If you're talking about AwlGrip, the two-part paint, I would highly recommend not spraying the stuff. It has an isocyanate (cyanide) based component that can be lethal if inhaled.



davidpm said:


> SD
> Do you have a link to a mask you have in mind? Also do they work with paint products like AllGrip too?


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## tager (Nov 21, 2008)

If it isn't rotten yet, and you aren't going offshore. Just leave it alone. Maybe try the dehumidifier. Re coring would be foolish as the core is still good.


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## tommays (Sep 9, 2008)

I am dealing with a wet plywood core right now 

1. I have had one 8" X 12" section of wood out of the boat for a week it is NOT getting dry 

2. There are many areas on my boat that while damp are BEST left alone as there is no delamination of the wood OR the inner and outer glass ,even the worst wood is still intact BUT is not bonded to the glass causing flex 


3. In my case i have to work inside as the inner skin is REALLY thin


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## sailingdog (Mar 19, 2006)

While worth a shot, I'd point out that this will likely only dry out the innermost layers of the plywood and that the uppermost layers will still be damp and rotting... The brown water you've been seeing is generally a sign of the wood rotting.



laHolland said:


> That's a good idea, Rosa. I think I will try that first, and then reevaluate.


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## NICHOLSON58 (Feb 22, 2009)

You can find industrial grade masks and respirators at safety equipment industrial supply houses to commercial business. Especially look in stores catering to automotive and professional painters. Try the upscale Sherwin-Williams industrial outlets. Any paint store that sells 2-part Urethane paints. Also look in McMaster-Carr on line. You want the mask with the screw-on replacement cartridges with the proper fill, such as activated carbon etc. it wont make you invincable but will protect from casual inhalation. 

BTW, I found very inexpensive white 2-part at Sherwin-Williams they sell for water tank lining and bilge water proofing. It did a really nice job below deck and chain locker. Pick the slow cure or you will be hustling.


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## mitiempo (Sep 19, 2008)

I'd suggest also that you will never dry it effectively in place. The moisture has travelled along the plies of the plywood far and wide and probably took ages to move throughout the wood. This is one of several reasons that plywood is such a bad core. It will continue to rot and freeze/thaw cycles in the winter will eventually cause delamination. I suggest complete removal of the wet plywood and a recore with either end grain balsa or a foam core. It is a tough job from below. A neighbor just had 1/2 of his cabintop recored which included removing wet plywood and it took a pro about a month to complete the job (32' Westsail) from below.


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## laHolland (May 22, 2009)

Tommays, I looked at the picture of your "coffee" leak and it is very similar to mine (Cal 27, pop-top). The interior FG is thin in many spots, or poorly laid, so it doesn't seem worth wrecking a perfectly nice exterior when the interior is kind of crap anyway. The problem is the frost-heave with the wet wood.. when it expanded in the winter, it broke apart the seam where the cabin ceiling meets the pop-top frame, which is where it is slightly oozing coffee. It took me a while to figure out why it was oozing from the HIGHEST part of the boat, rather than a lower spot, and an area that isn't near any source of potential water intrusion.. it's oozing from that spot because it's the only area with an open seam to ooze from.


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## Sanduskysailor (Aug 1, 2008)

*wet plywood core*

As others have said you need to remove wet core. Attached is a picture of the plywood core in the cockpit sole of my boat. The boat was inside in a heated dry shop for two months before we cut the skin off and started removing the core. The plywood was totally delaminated and dripping water. Wow. Interestingly due to the heavy lay up there were no gelcoat or stress cracks on the sole. The pedestal would deflect the deck when leaned on but not that much. Fortunately my surveyor caught this and the buyer adjusted the price which covered the cost of the repair.

For those interested, the repair entailed a new plywood core with the center section being sold glass. This means that in the future the sole penetrations for the pedestal and rudder post will be through sold glass with chance for the plywood to get wet.


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## idontwantanaccount (May 18, 2005)

Saw an interesting thread on another board discussing the use of microwaves to dry core.

Using Microwaves to Dry a Wet Deck Core - Cruisers & Sailing Forums


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## CharlieCobra (May 23, 2006)

One of the things you'll see posted on sailing forums is the old "drill a lot of holes and inject penetrating epoxy into it" trick. Let me tell ya, it don't work. All you end up with is sheets of rotten ply with lots of little epoxy towers in it. A PO tried this with Oh Joy's decks and I personally saw the results when I tore them off.


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## Sanduskysailor (Aug 1, 2008)

*next steps in process*

Here are some new pics of the plywood core adventure. One shows plywood and balsa cores laid in. The next shows the old skin placed on top as a template to drill new holes.


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## doslocos (Mar 10, 2010)

When working on boats in San Diego having problems such as yours and with wooden boats with rot, we used a substance named "Git Rot". It is a very viscous form of epoxy. The major advantage of it was that it would wick just like water and would drive water out by replacement and heat. Be careful with it as just like other Epoxies it gets hot. If you know where the wet is you can drill small holes into the affected area usually 3" apart and inject the Git Rot. There are probably other products on the market by now as the last time I used this stuff was year 2000. By the way do not drill all the way through just into the core. After you are done fill the holes with epoxy with no filler as the filler weakens the epoxy.The holes should be only big enough to insert a syringe so if you know someone at a hospital get one with a needle.


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## NCC320 (Dec 23, 2008)

All these issues with wet cores (plywood or balsa) seem to be a good reason, if one can avoid it, not to buy an older boat where you know some of the fixture holes will have leaked. It seems like it turns a "bargain" into a nightmare. You spend lots of hours, money, stress to try to fix the problem, and for most of us, it would look horrible when we finish. Maybe, smaller/newer vs. older/larger boat when shopping for a boat would make sense to minimize these problems.

That said, why do the manuafacturers continue to use plywood and balsa? In the old days, the alternatives were few, but today there are lots of "none deteriorating in presence of water" alternatives. Most foams don't seem to behorribly expensive.

Also, unless it's too bad, maybe the solution is don't worry about it. You bought a boat with some problems, use it and enjoy it. The core problems will get worse and you'll have to discount the boat a bit more when you sell it (owning boats also always is a costly situation).


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## LookingForCruiser (Feb 7, 2007)

NCC320 said:


> That said, why do the manuafacturers continue to use plywood and balsa? In the old days, the alternatives were few, but today there are lots of "none deteriorating in presence of water" alternatives. Most foams don't seem to behorribly expensive.


Any time water can get into a core, regardless of material, you're going to have delamination issues. Foam isn't a panacea. It won't rot, but will still fail when water wicks along it. You still have to cut the whole deck apart to fix the problem properly.

I wouldn't bother with injecting epoxy. If you're going to fix something, fix it once the right way, instead of doing something cheap and half-assed and then have a bigger problem down the road because the rot has continued.

I also don't recommend working from below, you'll get a weaker laminate because gravity is working against you - the core won't have a great bond with the top skin, and will very likely have voids.


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## Sanduskysailor (Aug 1, 2008)

"It seems like it turns a "bargain" into a nightmare. You spend lots of hours, money, stress to try to fix the problem, and for most of us, it would look horrible when we finish. Maybe, smaller/newer vs. older/larger boat when shopping for a boat would make sense to minimize these problems."

A lot of bad assumptions here. One, the boat in question was purchased last year and the problem revealed in the survey. Agreed on selling price was adjusted downward to reflect the cost of repair. Two- This job is being done professionally. It is being done right and the problem won't be an issue in the future. Three. The job is costing $2800 which was covered in the purchase price reduction.. Four- your assumption that newer and/or smaller boats won't have delamination problems is flawed. I know of numerous 10 year old boats with core problems due to shoddy manufacturing and design processes. It happens. Foam cores have problems too if you get water penetration. Five- the only stress I have had so far is getting enough light to take the pictures.


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## doslocos (Mar 10, 2010)

Blisters on a boat that is 1.25" thick is a nuisance. Blisters on a boat that is three ply thick is a major catastrophe. Many of the never boats are developing blisters and beside, sit in the V-berth and watch the sides oil can and how you can see light through them. Newer is not better and can in fact be far more dangerous.


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## sailingdog (Mar 19, 2006)

*I'd point out that GITROT does nothing to drive out the previous moisture, and will not work at all if the wood is wet, since the water in te wet wood will interfere with it curing properly.* Also, filler does not weaken the epoxy. If it really did so, why do all the guides on boat building recommend using filled epoxy for STRENGTH???

From the directions for use:


> Boatlife Git Rot pours into the finest openings, penetrates, and saturates rotten wood. GIT Rot cures into a resilient adhesive, *which arrests dry rot* by bonding wood membranes together with a mass stronger than the original wood. 2 Part Kits.
> 
> *Use on dried out, rotted, and weathered wood*, Also excellent for window sashes, gutters, boat stringers, transoms and keels.


*
What part of DRIED OUT and DRY ROT do you not understand. * I really hate when people recommend something that is not going to work and cost the OP money that is better spent elsewhere. 



doslocos said:


> When working on boats in San Diego having problems such as yours and with wooden boats with rot, we used a substance named "Git Rot". It is a very viscous form of epoxy. The major advantage of it was that it would wick just like water and would drive water out by replacement and heat. Be careful with it as just like other Epoxies it gets hot. If you know where the wet is you can drill small holes into the affected area usually 3" apart and inject the Git Rot. There are probably other products on the market by now as the last time I used this stuff was year 2000. By the way do not drill all the way through just into the core. After you are done fill the holes with epoxy with no filler as the filler weakens the epoxy.The holes should be only big enough to insert a syringe so if you know someone at a hospital get one with a needle.


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## sailingdog (Mar 19, 2006)

Foam just changes the problems that you will have. While foam core materials are not subject to rot, they do allow water to migrate and delaminate far greater sections of the deck in a short period of time than does balsa. Plywood has the worst characteristics of both foam-allowing water to migrate long distances-and balsa-rotting. It is also the worst material in terms of weight.



NCC320 said:


> All these issues with wet cores (plywood or balsa) seem to be a good reason, if one can avoid it, not to buy an older boat where you know some of the fixture holes will have leaked. It seems like it turns a "bargain" into a nightmare. You spend lots of hours, money, stress to try to fix the problem, and for most of us, it would look horrible when we finish. Maybe, smaller/newer vs. older/larger boat when shopping for a boat would make sense to minimize these problems.
> 
> That said, why do the manuafacturers continue to use plywood and balsa? In the old days, the alternatives were few, but today there are lots of "none deteriorating in presence of water" alternatives. Most foams don't seem to behorribly expensive.
> 
> Also, unless it's too bad, maybe the solution is don't worry about it. You bought a boat with some problems, use it and enjoy it. The core problems will get worse and you'll have to discount the boat a bit more when you sell it (owning boats also always is a costly situation).


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## laHolland (May 22, 2009)

Wow, a lot of strong sentiments regarding this subject. We have peeled away the inner fiberglass laminate to reveal all of the plywood core in the problem area. When we checked on it yesterday it was nearly dry, though as it dried we were more clearly able to see that some sections of the plywood had rotted (as many of you suspected). So we will be cutting out the affected area (1.5' x 2.5') and replacing it with new plywood. I know plywood perhaps isn't the ideal core material, but the area requires a very rigid material for supports, and I don't want to use different core materials side by side.

Since we were given the boat "free of charge" (in quotes, because of course we paid for registration, insurance, launching, dock space, storage, etc.), I'm completely happy to spend my time and money working on it. I still feel like I got a bargain, even after sinking $2000 into various projects thus far. It's certainly a "project" boat, but we are having fun with her and it's been a great learning experience, and we didn't have to take out a loan to make it happen. And when I look around the boat yard, I see plenty of younger boats that are busy being worked on as well.

I'm a novice at all this, but I figured getting into it that when you purchase an object that spends most of it's time floating in water, with extreme forces applied to it on a regular basis, and that said object provides shelter and safety for those aboard, I counted on the fact that maintenance would be chronic and ongoing. So far I haven't been disappointed by this assumption


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## doslocos (Mar 10, 2010)

Yes as you go along you will get 20 answers from any ten people on any subject and all of them different. Enjoy the yards, I always found them fascinating and instructional. Look to see if you can find any other boats like yours and then talk to the owners about what they are doing and why. One thing that will happen to you over time is you will start asking people you trust for advise and then decide what you are going to do yourself. When that happens then you will be a real boater. Took me about five years to understand that I knew as much as anyone else. Then another five to understand what I didn't know and who to trust for the best answer. Project boats are the ones you will always remember as those are the ones you learn from. Best to you and enjoy.


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## NICHOLSON58 (Feb 22, 2009)

If I was ripping out wet wood, especially in a non-racing boat, I would re-build with Fab-Mat (heavy fiberglass mat) and epoxy. It will never trouble you again. I also suggest checking out my microballoons and epoxy filler job on our rudder in my gallery on this site. http://www.sailnet.com/photogallery/showgallery.php/cat/500/ppuser/159746/sl/n I filled and faired the thing and hauled it to my marina shop to have the skin vacuum bagged. Torresen's guys looked at it, thumped it and remarked it would never give us any trouble ever again. The filler has a yield of 3000 psi, its extremely light and totally waterproof. With skin bonded to it, it will out-live the hull. Epoxy and foller from Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc. makes it affordable.


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## zz4gta (Aug 15, 2007)

Recore the really wet spots. If it's just damp don't worry about it. Mine was leaking water through it when it rained. I decided it was time I did something about it. The length of this was over 6' and the width was probably 2'. Need to do the foredeck and portside at some point.  After I faired it and painted the inside, it looked like a new boat.


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## doslocos (Mar 10, 2010)

Very nice job on the deck repair. I agree that the best solution is to re-core and appologise to anyone that took my previous comment to be a better way to fix. I submitted it only as a less expensive alternative and not a long term solution.


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## swanson27 (Apr 29, 2013)

Hi I have a swanson 27 with the same core problem.

I would like to see if there is anything wrong with pulling all the inside fibreglass skin off, removing the the core and just replacing it with supporting arches/ribs made of wood or fibreglass ? Seems like less work and I would not have this problem again ?


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## tommays (Sep 9, 2008)

The best way to understand it is the outer skin, core and inner skin form a really strong I-BEAM in a very thin space

If you don't have one of the three the beam bends pretty easy


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## arf145 (Jul 25, 2007)

Which means, no that wouldn't do it--you need a core. That way you've got an I beam in all directions.


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