Hull balsa core replacement advice

Hello all,

I have a 1993 Freedom 40/40 sailboat that I purchased a couple years ago. During his sounding, the surveyor noted a "void about 12"x6"" near the shaft strut, that was probably delaminated. We also noticed some water dripping from the shaft strut where it met the hull.
It has been on the hard this past summer while I tinkered with some upgrades and minor repairs. During this time I noticed some water constantly dripping from an area of delamination along the side of the shaft tube. I procrastinated and am just now starting to work on this before getting splashed (hopefully) this spring/summer.

Make a long story short, everyone with a cored hull's worst nightmare: started cutting and peeling off the outer laminate with the intent of digging out the wet core and re-glassing, and the cutting just kept going and going and going. It seems at least half the port side has wet core. I'm estimating about 80 square feet from just forward of the rudder post to amidships, from the bottom almost centerline up to the waterline. About 50-60% of that is seemingly solid core, just wet. The rest is dark, stinky, and mushy. Most areas the outer laminate is pretty difficult to remove, so adhesion is good, just wet core underneath.

I've already purchased this boat, I owe a little more money on it, and have already invested about 20% of what I paid for it on upgrades and work, so throwing it away or selling it are not options. A quick search says paying for repairs ranges from $300 to $800 per square foot; that is not an option financially either. I will talk to the boat yard she has been in this summer/winter, but they are small and I don't have the best confidence in their abilities. Talking to other local repairers will be next, but I don't expect that route to be financially feasible either.

I am fairly technically competent, although not experienced with this situation. I understand the general process of this repair, but have some questions on the details:

1. I have removed a lot of the outer laminate. I would like to remove more, but I am restricted now by the poppets, and I understand that too much removal may cause flexing of the hull or some other unwanted distortion. Have I gone too far already?
Is it advisable to do the area I can now, finish the outer laminate, and then do the rest? Or is it more important that it all be done in one shot?


2. My tentative material choices:
-epoxy for waterproofness and superior adhesion
-balsa core for price
-cloth is where I lack knowledge, I'm just now learning about all the different strand orientations and such. I don't know the original schedule, but what is recommended here? From almost horizontal near the keel to almost vertical at the waterline.. It's quite a bit thicker near the keel, as makes sense, but is there different engineering for different areas? Most other forums just say slap it with 1708 and call it a day.

3. I may have to compromise in some areas and leave some sections of the good but wet core, most likely at the waterline, "slightly" wet. My thought was to dig out a couple inches of the core there, stuff with thickened and reinforced epoxy, and proceed as normal, kind of locking in the moisture in that area. Is this totally dumb?

I know I have other questions, but my brain is fried for now. Thanks for reading a long post.

You have my sympathy.Lots of it,because what you are dealing with is an absolute nightmare.I recommend investigating whether the surveyor who examined the boat has good liability insurance and seeking to recover some of the costs from his insurers as he may have been correct about some delamination,but should have investigated the full extent of it,unless instructed to the contrary.

Forget any thoughts of sailing this year as what you are doing is a mammoth job and I wouldn't have recommended doing it that way in the first instance.We have a situation where a novice will be attempting to apply a core while working against gravity and hoping to achieve a bond that can be trusted to take him and his family and friends to sea and bring them back.To say nothing of the challenge of getting a decent finish over the entire area,which has yet to be accurately determined.

I would have started from the inside and I would have worked hard to first investigate the path by which the water infiltrated the core.It is entirely possible that there may be a poorly bedded deck fitting allowing the water in and damage may still be spreading.For the time being,the exact nature of replacement fibres and resin is pretty academic and I have no idea which "other forums" the commentators are offering advice on.There does seem to be a default reaction of some who fancy themselves as experts to parrot "1708 and epoxy" for everything when a lot of them have little more experience of working on boats than hosing guano off their decks.Ask them to show you the boat that they last carried out similar work on before being led down that path.

It gives me no pleasure to spread gloom,but a dose of realism has to be applied.

I watched , funnily enough, the owner of a Freedom 28, dig around the bolt hole of his sheer leg, only to end up having to cut at least 3ft fore n aft and maybe 2 ft below the waterline due to soggy balsa. He got the resident pro on the job. Once back to sound balsa the repair area was tented under plastic with Infa-red heat lamps on ,for some days until readings were suitable for whatever brand of epoxy he used and the balsa sheet was laid in with the help of plastic sheet and low pressure vacumn pump. Followed up by several days of glass sheathing under vacumn, and then a whole load of fairing and sanding and a total respray.
Obviously the layup had to match the existing, probably a mix of CSM, woven rovings and finish cloth. Its certainly DIY able, but its certainly testing when working overhead. A slow cure resin means you can do the job in several bites.

wet feet said:

You have my sympathy.Lots of it,because what you are dealing with is an absolute nightmare.I recommend investigating whether the surveyor who examined the boat has good liability insurance and seeking to recover some of the costs from his insurers as he may have been correct about some delamination,but should have investigated the full extent of it,unless instructed to the contrary.

Forget any thoughts of sailing this year as what you are doing is a mammoth job and I wouldn't have recommended doing it that way in the first instance.We have a situation where a novice will be attempting to apply a core while working against gravity and hoping to achieve a bond that can be trusted to take him and his family and friends to sea and bring them back.To say nothing of the challenge of getting a decent finish over the entire area,which has yet to be accurately determined.

I would have started from the inside and I would have worked hard to first investigate the path by which the water infiltrated the core.It is entirely possible that there may be a poorly bedded deck fitting allowing the water in and damage may still be spreading.For the time being,the exact nature of replacement fibres and resin is pretty academic and I have no idea which "other forums" the commentators are offering advice on.There does seem to be a default reaction of some who fancy themselves as experts to parrot "1708 and epoxy" for everything when a lot of them have little more experience of working on boats than hosing guano off their decks.Ask them to show you the boat that they last carried out similar work on before being led down that path.

It gives me no pleasure to spread gloom,but a dose of realism has to be applied.

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Thanks, wet feet, for the sympathy and realism, both are appreciated along with the advice.

I did just finish talking to the boatyard she has been in all summer/winter, and they have no problem with another summer/winter on the hard. So I have plenty of time to do it right. Now I just have to rent out my Docko..

I believe that the ingress started from the shaft strut, as the rot is the worst in that area. It looks like they used a very small buffer of resin with a tiny amount of milled fibers around the shaft strut before the balsa. Maybe half an inch in some places. Amazingly though, the starboard side seems unscathed, even though it is inches from the edge of the strut. Whatever barrier or construction they used along the centerline seemed to isolate fairly well. (The shaft/strut on my boat is offset about 6-8" to port). In any event, the moist core closest to the waterline seems orders of magnitude better than that closer to the keel. I'm pretty certain the leaks originated at the bottom. The shaft tube area also seems like a culprit for the same reasons.

Other forums, and other searches, almost entirely show results for deck core replacement. It's been difficult to find good advice and examples for the hull. Some similar aspects, perhaps, but when I started learning about the engineering involved in hull layups, I thought it best to ask the experts here.

skaraborgcraft said:

I watched , funnily enough, the owner of a Freedom 28, dig around the bolt hole of his sheer leg, only to end up having to cut at least 3ft fore n aft and maybe 2 ft below the waterline due to soggy balsa. He got the resident pro on the job. Once back to sound balsa the repair area was tented under plastic with Infa-red heat lamps on ,for some days until readings were suitable for whatever brand of epoxy he used and the balsa sheet was laid in with the help of plastic sheet and low pressure vacumn pump. Followed up by several days of glass sheathing under vacumn, and then a whole load of fairing and sanding and a total respray.
Obviously the layup had to match the existing, probably a mix of CSM, woven rovings and finish cloth. Its certainly DIY able, but its certainly testing when working overhead. A slow cure resin means you can do the job in several bites.

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That seems like a workable approach, skaraborgcraft, thanks. If I understand correctly, would the recommended process be to vacuum bag the core to the inner laminate, and let it fully cure before moving on to the outer laminate? Or should everything be done in one shot (core and outer laminate)? I like the idea of doing things in several bites, but I'm not sure where the bites should be taken.. I read one recommendation that said each layer of laminate, at least when working upside down, should start to kick before applying the next layer, so that it's sticky enough to withstand drooping with the weight of multiple layers, but still have a decent chemical bond. Something like that?

Also, now that you mentioned the heat lamps and I have time to slow down, I can think about letting the edges of good but moist core dry out over the summer and attempt the actual repair in the fall when it's a little cooler. It will probably require some plastic covering to keep the rain out if it has any chance of drying.
There is a gentleman in RI who ran the Freedom shop back in the day who may be able to recommend the original layup.

Researching the original layup can only be a good thing.From where you are currently it would be best to aim for sealing the leak path as a matter of some priority and then applying a new core.Adding the core without vacuum bagging would be sketchy at best and attempting to vacuum bag overhead and before the resin kicks would be challenging in any situation-a practice run on something would be sensible..It could be done in stages until confidence is gained.Laminating overhead is pretty miserable and protection needs to be worn.Fairing overhead is something to be dreaded,but perseverance will get you there eventually.

SeaSkwerl said:

If I understand correctly, would the recommended process be to vacuum bag the core to the inner laminate, and let it fully cure before moving on to the outer laminate? Or should everything be done in one shot (core and outer laminate)? I read one recommendation that said each layer of laminate, at least when working upside down, should start to kick before applying the next layer, so that it's sticky enough to withstand drooping with the weight of multiple layers, but still have a decent chemical bond. Something like that?

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I watched the core being put in, hull was coated with resin, back of balsa had a coat and went to tack phase and was then laid in by hand where it stuck without any issue, and then vacumn bagged. I believe he was using West products, and his experience said that "chemical bond" does not just switch off at a specified hour. I assume everyone knows the amount of testing the brothers did with epoxy, and that the time schedules they reccomend has a safety factor built in. Certainly he had no issues in 30 years with a lack of chemical bond failure by coming back the next day to do the following lay-up. I will say working in the soggy SW of the UK may have helped and if working in a dry arid California, things may differ a bit!
You should be able to measure the thickness of the layup with calipers, but getting the actual lay-up schedule to replicate would be best.

Lets not forget, ALL repairs done on fibreglass boats are relying on a mechanical bond somewhere, I would say surface prep and cleanliness and a wide feather contact between old-new is paramount.

1. If you remove to much of the core there is a distinct possibility to warp the hull. You have to watch out for that. Replace what you already exposed first.
2. Materials are a personal choice. You can do the entire job with polyester if you like. You must match the original skin thickness of the removed fiberglass layup (measure the removed or still existing skin). The original was probably a woven rowing/csm alternation, wich is very quick in building thickness. You can only replicate that when using polyester, if you use epoxy you should not be using csm. Many people do use 1708 with epoxy, but in my opinion it's a waste of resin. With epoxy I would use a heavy biax or triax without csm and more layers.
3. At this stage there is no reson to leave wet core in place. Either dry it out or replace it.

When you laminate the first step is to lay the balsa sheet over a barrel so the spaces between the little cubes open up, then you give everything a good brushing with unthickened resin, followed by thickened resin. On the fiberglass skin you apply thickened resin with a notched trovel. Then you stick it to the hull with vacuum or screws and let it cure. Fiberglassing is usually a separate step.

Letting the wet balsa exposed over the summer is a gamble. It could dry out or it could rot. I wouldn't do it, but that's you decision.

Rumars said:

You can do the entire job with polyester if you like.

if you use epoxy you should not be using csm.

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Secondary polyester to polyester bonds will not be as good as an epoxy.

You can use epoxy with CSM, have done so myself, the finish is usually a bit milky coloured.

Chopped Strand Mat and Epoxy - Epoxyworks

skaraborgcraft said:

Secondary polyester to polyester bonds will not be as good as an epoxy.


You can use epoxy with CSM, have done so myself, the finish is usually a bit milky coloured.

Chopped Strand Mat and Epoxy - Epoxyworks

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You are correct in that epoxy will bond better, what people forget is that a resin only needs to bond good enough to not fail. If it will experience 100 lbs of stress, and polyester will survive 200 lbs and epoxy 300lbs, it means they are equal in their abilities to succeed. This is what people that have been doing this exact type of repair for many decades understand.

Again, I'm not saying epoxy isn't better, but how much better than completely successful do you need to be.

As for CSM with epoxy, it's sort of just the opposite. CSM provides comparatively little strength for its weight and then you need to add in the amount of epoxy used to wet it out. What you end up with is a heavy and low strength portion of the laminate that has a high cost. One of the big advantages of epoxy is that you can choose fiber types and their orientation that meet your exact requirements with no extra fluff. If you add back in that extra fluff, why use epoxy.

I'm glad ondarvr introduced the topic of stress as it is at the root of many boatbuilding decisions.Quite a few years ago there was a TV advert here in the UK that featured a man whose overalls had been pasted to a board which was suspended to a helicopter in flight.It was supposed to impress,but given the considerable bond area and resulting low stress,it didn't actually prove much.With a sandwich laminate we might speculate regarding which zone is the weak link and it seems that the bond between the core and the outer laminate on this boat was sound.This bond has now been eliminated and will need to be replaced and the question is why one might wish to select a different material to that which worked and which would cost a lot less that the revered alternative.

A good cover would be a very useful thing to have as it would allow working in less than perfect weather and might hasten the drying process if the balsa hasn't deteriorated to the point where it absolutely has to be replaced.Once dry a coat of resin to keep the moisture out would be a good move.Tracking down the point where the water got in is really important.

ondarvr said:

One of the big advantages of epoxy is that you can choose fiber types and their orientation that meet your exact requirements with no extra fluff. If you add back in that extra fluff, why use epoxy.

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I only mentioned CSM as it would have been most likely in the original layup. Yes, better fabrics can be used if the laminate thickness allows.

I have not done any major grp core repairs, but those that i know have, always used epoxy. I have no issues using polyester on a new project. Given the severity of the repair i would splash the extra for epoxy and sleep better.

wet feet said:

a few years ago there was a TV advert here in the UK that featured a man whose overalls had been pasted to a board which was suspended to a helicopter in flight.

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Ha! Solvite wallpaper adhesive.

Is the 80 square feet of bad core the entirety of it or is the discovery of soggy core still ongoing?

Are there any bulkheads? Stringers?

You have to support the hull much more. Build some wooden shape keeping support . It would be good to make the hull lighter if you can remove something from the inside or outside.
A large transparent tarp , airflow and the sun should dry the hull. I would remove all the laminate from the submerged part and if it is wet above the waterline, that too. You can drill thousands of ventilation holes.

If it dries, you can think about what to do next. Foams, replacing parts of the core, epoxy putty.

Thanks so much for the advice everyone, my confidence is slowly building.

Let's see if I can answer some questions.
The extra adhesion of epoxy, and the ability to substitute at least one layer of CSM with cloth, make me feel better enough to justify the extra cost. The extra cost of foam over balsa, not so much.

There is one bulkhead and a few stringers across the area. I will definitely not peel any more outer laminate, and will finish the majority of the outer layup before moving poppets and doing the rest. The areas adjacent to the part I've already peeled, those being held by poppets, are areas that seem relatively secure.
I will definitely do the tarp and air and sun assisted drying as much as possible. I've read about heat lamps and vacuum systems, but they seem unnecessary. Never thought I'd wish for a really hot summer...

I would say about half the newly exposed core is just wet, not compromised. "Wet" meaning that water drips off of a sample when squeezed by my fingers, or drips off the tip of a screwdriver when poked into the core. The sections that I think are salvageable are just barely showing any water when squeezed. I can tell it's wet, but it's hard to see. I have a reference area that is bone dry and super solid.
Where the outer laminate was removed over the "decent" areas, a layer of CSM partially stayed with the core. Looks fuzzy in the pictures. Not sure if this is a good sign that the core is still good, or a bad sign that there was some kind of failure between the CSM layer and the following layer (both?). But I can still get water to come out of these areas by poking it with a screwdriver.
I'd say a good 1/4 of the whole area is so delaminated or mush that the core just flops off when the laminate is peeled. The rest is somewhere in between. Regardless, if I've exposed the core, it's getting replaced. My biggest concern is the iffy areas that border the cuts.

I just got off the phone with one of the original builders, and while he had many great suggestions he did not have any specific advice on the actual layup schedule. I tried by email and phone to get in touch with the original designer, David Pedrick, but was unsuccessful. The builder, Paul Dennis of Warren River Boatworks in RI, suggested that I have the outer laminate sections that I removed tested and analyzed to determine the layup. He said they burn the layers off. Has anyone used such a service?

If this service is too price prohibitive, as I imagine it may be, what are my other options for the replacement skin? Would a generic, say, 0/45/90/45/0 layup, using epoxy, no CSM, same thickness, overcome any deficiencies of not replicating the original schedule? I haven't taken calipers to it yet, but the majority of it looks somewhere around 0.2", almost definitely less than 0.25", but more than 0.125". The laminate closest to the keel is easily twice as thick; I'm sure there was a specifically engineered layup in that area.. Obviously having the original design is best, but what if that is not available?

Regarding the core, he said that their limit was no more than 18% moisture before doing the layup. I don't have a moisture meter, but I do have some pretty accurate scales at work; if I weighed a sample of core before and after desiccating it, would that give me an accurate idea of moisture level? And if so, what would a realistic number be before claiming "dry enough" for layup?
He did mention that he has done a few repairs of both of the areas that I suspect were the original water ingress points, so between that and the absolute horrible rot in those areas I'm pretty confident the root cause is known.