Replacing Balsa Core - Few Questions

[Pburk]

Hello all,

I have a 1992 16 foot cruiser that had a mushy spot. I pulled out the seat panels and started cutting and it was a total horror show. More water than balsa. I've been reading a lot of posts on this but have a couple specific questions and would really appreciate any thoughts. I'm not going to say I'm totally over my head, but I'm close...

-When to say when? I have the worst bits out (almost the entire port side and under both seats). The rest of the balsa seems to be normally colored and well adhered to the bottom and top layers of fiberglass with no obvious staining, etc. That said, my cheep moisture meter is still registering 40% + in some of these locations.

- Any problems with using two layers of 3/4" balsa? I'm having trouble finding 1- 1/2"

- Do I need to find a way to jack the boat up off the trailer to keep the bunks from deforming the hull?

- It's pretty high humidity in the PNW at the moment. If I leave the new balsa to come to equilibrium, is it ok to install, or do I need to wait until summer? I'm under cover, but not outside.

-Aside from making future access difficult, Is there any reason to not just fiberglass the seats and side panels in when I reinstall?

Really appreciate any thoughts!

[thataway]

[quote="Pburk"]Hello all,

I have a 1992 16 foot cruiser that had a mushy spot. I pulled out the seat panels and started cutting and it was a total horror show. More water than balsa. I've been reading a lot of posts on this but have a couple specific questions and would really appreciate any thoughts. I'm not going to say I'm totally over my head, but I'm close...

-When to say when? I have the worst bits out (almost the entire port side and under both seats). The rest of the balsa seems to be normally colored and well adhered to the bottom and top layers of fiberglass with no obvious staining, etc. That said, my cheep moisture meter is still registering 40% + in some of these locations. I would try and dry the balsa out, if obvious moisture. Also using epoxy at this interface is going to work better than polyester resin--Vinyl Ester is a compromise. The worry is going to be freeze thaw cycles--try and avoid that.

- Any problems with using two layers of 3/4" balsa? I'm having trouble finding 1- 1/2". No problem with two layers of 3/4". I would use a resin thickened with cabosil between the two layers.

- Do I need to find a way to jack the boat up off the trailer to keep the bunks from deforming the hull? Put a straight edge on the area removed and see if the bottom is out of true. Usually it is not necessary to try and support this area better. If I had to, I would use a flat sheet of at least 3/4" plywood over the bunk to spread out the load. Size of the plywood would be slightly larger than the area repaired. Any grade of plywood would work.

- It's pretty high humidity in the PNW at the moment. If I leave the new balsa to come to equilibrium, is it ok to install, or do I need to wait until summer? I'm under cover, but not outside.
Temperature is more of a concern. I would just go ahead and re-laminate. You want the new core material to press down well to the bottom layer, which should be absolutely clean- Depending on the surface, it may be a good idea put a thin layer of mat down first, with slightly thickened resin.

-Aside from making future access difficult, Is there any reason to not just fiberglass the seats and side panels in when I reinstall? Go right ahead and tab the seats down. I have a photo in my album where I have removed the "L" brackets, filled the hole, and used small tabs. I feel that is the way the "furniture" should have been secured in the first place, and then you would not be replacing the core. My Caracal is undergoing repairs, and we will tab the center console down. You can always cut the tabs with an oscillating saw.

Really appreciate any thoughts!

[Marco Flamingo]

[pcg]

[Pburk]

Thanks everybody. It sounds like the 'clean' looking balsa is still too wet even though it seems well adhered, and my next step is to at least pull off the fiberglass and rig something up to try to dry it out. That seem right?

I'll admit that I was hoping I could call it quits when I got rid of the mucky stuff, but I already have about a 1/4 of the core removed, so might as well do it right. I'll also go ahead and give the factory a call about the balsa.

I'll keep you all posted!

[thataway]

A few thoughts: Marco and I are not as far apart in thinking as it might appear. Moisture meters (especially the cheap ones) measure the surface moisture--they don't penetrate deep. The "gold standard" moisture meters are the Tramex SMM5 Skipper 5 Marine Moisture Meter Cost: $635. Even they measure "relative moisture". I use a "General" or "Ryobi" moisture meter (Pinless), with several different modes. Cost: $50. The moisture meter is only relative.

David Pascoe (RIP) was somewhat controversial. Here is one of his articles on moisture meters.. He makes a number of points: core material that is cut into small blocks, which is what is allows for bending and conforming to the curve. The gaps between the blocks are known as "kerfs" while the loose weave fabric holding it together is called a "scrim." The side of the coring that goes up against the skins already laid into the mold is known as the "blind side". This is because the laminators cannot see through the core material to see how well it is making contact with the outer skin. assuring uniform contact with the core is a major problem except when vacuum bagged, Balsa wood is highly absorptive – as are all woods – on the end grain axis, whereas perpendicular to the cell length or grain direction it has been shown that balsa does not absorb water well. Were it not for the kerfs in the balsa or foam, neither material would transmit water throughout. Unless vacuum bagged, it is impossible to assure that the kerfs are completely filled with resin, and it is these unfilled kerfs that permits water migration through all cored structures.

Were our boats vacuum bagged? I do not know in the past, but my impression is that there was little if any vacuum bagging earlier than 2012 or so.

Water migration is aided, particularly on hull bottoms, by the forces of water against the hull. This creates a pumping, hydraulic effect that serves to distribute water throughout the core.

If the void areas in the core are completely water-filled, the hydraulic action will become so powerful that it will reduce the core to a slurry of fibers or mush. This, then, is a total catastrophic core failure after which the skins are likely to fracture. Balsa has been shown to break down through three different mechanisms, hydraulic erosion, fungal degradation or rot, and a lesser known and understood form of corrosion. As oxygen starvation can cause severe corrosion of metals, it can also cause corrosion of wood..

Part of the problem in answering this question comes from the fact that we cannot determine whether we are reading moisture behind the laminate versus within the laminate.

This is the fundamental problem with trying to meter hulls for wet cores; the meter won’t tell us what part is wet, the skin, the core or both.

So we don't really know what the real saturation of a core is without drilling into it.

Basics are that polyester laminate is a "semipermeable membrane"--but it takes years and high pressure for water to migrate thru the polyester surface laminates--of any thickness.

To get the water out, you have to drill holes, or cut sections out--and even then, you don't know how much of the water is out.

I have followed several cored boats where using hot vacuum, (where thousands of holes are drilled in the laminate, then sheets of material are placed over this laminate, and heat plus vacuum is applied. Some times this takes as much as a year to dry out.

If one gets the laminate "dry" in XX Days, then there was not a saturated core. Or you have dried the surface of the fiberglass laminate and you don't know what the core is like.

Yes, absolutely theoretically it would be ideal for the rest of the core of the boat to be dry. But we don't really know how much the core is saturated (with out test drilling), and to bring this moisture out, with heat is difficult.

I do want to make one point here--and that is using electric heaters, unless ignition protected, is a potentially dangerous issue when working with various resins, which have very volatile hydrocarbons (explosive) as solvents. No open flames, no surface catalytic and any heaters which may spark when make or break contacts, if there is any "fresh" resin around.

The point of this, is that you might wait until next year using heat and low humidity, and still not dry out the core--Unless you have "escape" path for the water molecules. Would it hurt to try and dry the material for a few weeks--not at all. Will you know if the core is dry? Not unless you sample it.

The question: - It's pretty high humidity in the PNW at the moment. If I leave the [b]new balsa to come to equilibrium, is it ok to install, or do I need to wait until summer? I'm under cover, but not outside.

The question was "do I let the new balsa come to a moisture equilibrium?", Not about drying the old core in this specific question... You want the balsa core to be as dry as possible--not adding more moisture to it. You do want a controlled temperature environment-- above 60* F. Ideally in the mid 70's for proper curing of resins.

There are other modalities which can also give us information: Infra Red photography, and Ultrasound can both play a role in determining the degree of moisture in a hull. Just keep in mind that the moisture meter is only one modality, and subject to many variations. After Hurricane Ivan, Myself and a top Non Destructive Test developer cut up 25 boats from a year to over 40 years of age, examining the laminates, and developing new testing equipment (for use in the marine survey field. Marine surveyors didn't want to pay for equipment (less than $3,000), so never took it to market.). To check the amount of moisture in a core, we cut the laminates off on one of the samples, and then baked in a 400 degree oven until "dry weight"--where additional drying did not decrease the weight any further. Moisture meters did not do a good job of assessing how much moisture there was present in both balsa wood and foam cores.

[pcg]

[Pburk]

Ok! I pulled out all the balsa from about 1' past the V-Berth all the way to the transom. All the remaining balsa looks clean and reads sub 25% on my moisture meter. I got into a pretty good rhythm of cutting the fiberglass with a grinder, then running an oscillating tool underneath and popping out 'bricks' of material.

Regarding the new core, I spoke to the factory, who didn't have any 1 1/2" to spare. They sent me to Composites One, who also don't have any 1 1/2" balsa anywhere in the country. So it looks like I'm going with a double layer of 3/4". Given this I have a couple follow up questions:

- Any idea how much epoxy I should be thinking about with two layers of core and fiberglass? If I need to buy in bulk I'd prefer to just go ahead and do it.

- When I start replacing material should I start with a layer of CSM and then the balsa? Or just start with the Balsa.

Thanks again for all the help! I also removed the rub rail, and am thinking pretty seriously about moving the batteries and putting in a new 'limpet' style gas tank. I'll pretty much have an all new boat when all is said and done!

[Reelin2]

Can you share some pictures of the project?

[thataway]

I prefer thickened epoxy over CSM (Chopped Stand Mat) in the first layer. The sizing in most CSM are not epoxy solvable, so the mat will remain stiff and utilize a lot of resin to be "smooth". Use Cabosill thickened epoxy resin. About equal volumes of the Cabosil and Resins. A notched trowel works well for that base layer. You want to push down, and spread out any of the thickened resin into the kerfs or voids of the balsa core. in small areas weights are useful to push the balsa to get the best layer next to the outside glass. If you can do a larger area ("cooler resin mix") then vacuum bagging even using a shop vac will do the job and give an excellent result. Also with the amount of core removed, this is where the support should be used under the hull to avoid any distortion (especially a void or hook aft).

I use the West Systems epoxy. The weight of 1708 biaxial fiberglass cloth is 17 ounces per square yard. It takes 51 ounces of resin, per square yard, to saturate it. There is also 1700 (no Mat) and 1808 cloth--each has a different function and is better for certain type of projects. We used to lay up alternate layers of woven roving and mat to build the thickness (and strength). The heavier rovings don't take epoxy as well as the stitched oriented fibers (1708 at 45* and 1808 at 90*) (Biaxial cloths)

There are some tables on the West Systems Epoxy web site (as well as many excellent articles) which estimate how much coverage there will be for lamination and fairing. In your case, you need to figure out a close estimate for the area you have removed the core. Marco and others have done this so they would have used approximately the same amount as you will use.

[Pburk]

Thanks all. I'll try to figure out how to get some photos uploaded.

I think I'm going to pick up my balsa and epoxy on Thursday and hopefully start moving toward getting this buttoned back up! I'll admit that I'm a little torn about jacking the boat off the trailer. I know I might build in a slight depression at the bunks, but I'm a bit worried that I might introduce a bigger twist or similar if I try to lift it off the trailer. Trying to figure out how to best do this...

[thataway]

If there is a "hook" (hollow part of the hull) it can cause a boat to porpoise. I would at least check the bottom with a long straight edge, and see if there is any indent where the bunks are located. Can you jack the boat up under the transom, then slip a piece ol plywood between the bunks and hull? The idea is to spread out the load.

[Salish_Explorer]

Just popping in to second the advice you've received here, and also the request for photos!

I'd also highly, highly recommend you get a copy of West System's fiberglass repair manual. It costs 6 bucks, can be read in an evening, and covers all of the topics you've asked about. Link below.

Last, I would be very curious to know more about what you are thinking about the 'limpet' tanks, was I have been considering the same for my own 16 (considering either bow or stern tanks). One guy on here (maybe even one of the folks above, I can't remember) mentioned doing it in the view cavity which sounded great.


https://www.westmarine.com/west-system-fiberglass-boat-repair-and-maintenance-book-318485.html?&utm_medium=cpc&utm_source=google&utm_campaign=%5BADL%5D%5BPLA%5D%20Electronics%20%26%20Navigation_Test&utm_content=autoag0000x21026653643&gad_source=1&gclid=Cj0KCQiA5-uuBhDzARIsAAa21T_PfeHu1febL1jYIHaRqF54Euh8fNo7vccEnE7Fn3OUy_NNfWB7FwgaAma0EALw_wcB

[Tom Hruby]

This is an interesting and long running thread. However, I did not see any mention of first trying to find out how the water got into the balsa. Were there cracks in the outside of the laminate or did the moisture come in from the deck? If the moisture is coming from a crack (however small) in the bottom one will need to identify where they are. As mentioned in a previous comment, one will need to drill a number of holes from the inside. I have had similar problems with a plywood hull covered in glass and epoxy. I found the the easiest way to identify the location of the leaks in the bottom was to pour some denatured alcohol into the holes drilled and look for where in the bottom the water/alcohol was coming out. This is also one way to remove the water and replace it with alcohol which speeds up the drying and kills any mold in either the balsa or the plywood. Once most of the alcohol has dripped out or dried, repairs can be made with penetrating epoxy. Total Boat has a penetrating epoxy than can be thinned by up to 50% denatured alcohol (I used 25-30% alcohol). Putting the penetrating epoxy into the holes on top allows it to permeate through the balsa and strengthen it. Any remaining alcohol with dissolve into the epoxy. Hopefully gravity will pull the epoxy all the way through to the bottom and seal the leaks.

[Pburk]

Woof. It hadn't even occurred to me that it might be a leak in the hull. The deck was a pin cushion of unsealed screws and it definitely seemed like the damage was radiating out from these areas, with the worst of the balsa damage concentrated around the screws for the passenger seat. In this zone it was like water and coffee grounds, no balsa to be found. I'll take a closer look at the hull in the next couple of days to see if I can see any damage.

As a quick update, I still haven't figured out how to upload photos, but I did figure out how to jack the boat off the trailer and get it leveled. I've removed pretty much all the balsa between the cuddy and transom and have it sanded clean. I have the first layer of balsa cut and am waiting for a warmish day to get it glued down. I also removed all hardware and have over drilled the holes such that they can get epoxy too.

In the meantime, I'm working on some other projects while I have things pulled apart, such as replacing the rub rail (would love any thoughts on the best replacement for this), a 'Limpet' style gas tank and adding some more organized storage.

This is all kind of a pain, but I'll admit that I'm enjoying it. It's really going to feel like MY boat, when all is said and done.