Balsa Core Delamination

[Brewkid]

Clay,

All I can say is I feel your pain.... I just got notification that I'm going to have to hit the road for a bit, so until then I'm just going to cut away/prep and plan on glassing when I get home.

Good luck my friend and If you need a sounding board to vent too, I'm here and will definitely understand.

R/
John
Scallywag

 

[Blue Rose]

John,

I would have a hole here and a hole there and at the end of the day it looks like the most of it will just have to come out anyway...

I totally agree it should all come out so you can make a large repair and not a bunch of little ones....

I was thinking that if those prediction methods worked reasonable well then you might have a better idea of how much and the extent of the core damage area under the cockpit deck. (The disappearing screwdriver was terrifying!) For me, the hard part of watching the video is the disappointment each time you had to cut back some more hoping that you've reached the end.

The amount of removal/repair is the same either way, but somehow it might it easier to know in advance that it's all got to come out instead of a little at a time.

It seems to me that the core should have been compartmentalized so water intrusion at one location doesn't spread the damage throughout the hull.

Jim

 

[thataway]

It seems to me that the core should have been compartmentalized so water intrusion at one location doesn't spread the damage throughout the hull.

If only....in a perfect world, there would be no screws into the floor, or water trapped.

The balsa core is usually laid in one section in the hull. I believe that one of the repairs recently was going to compartmentalize the core into several areas. This means putting in a "barrier" of glass all of the way athwartship.

The problem is several fold. We see in Brewkid's situation that there was poor initial adhesion to the outer lamination of the hull (that which is first laid down in the hull. It was probably allowed to cure, --and maybe contaminated?? before the balsa core/ with scrim was put down. When restoring the balsa, the balsa should be brushed with resin (epoxy being far better) and then thickened epoxy laid on the floor with the balsa core laid on top and then weighted or vacuum bagged.

The problem with balsa core is that it is cut with kerfs so that the core will bend with the arc of the bottom of the boat. These areas of kerf are often resin starved and a channel for water to migrate. The screw driver is probably going into one of the kerf areas.

The other issue in Brewkid's boat is that it has the double floor--which is currently not removable. It will have to be cut out before he can even assess the back of the hull itself.

In testing with the phenolic or brass hammer (or even moisture meter) one would not find that areas of delimitation from the outer hull.

Yes, I would worry about the contour of the hull as it is re glassed. Initially the boat is laid up in the hefty mold. You want to maintain the smooth lines of the bottom of the hull.It may be necessary to put additional support under the hull.

 

[Brewkid]

I just dropped a couple more videos.

One that covers a little detail about the raised deck to give a visual to Bobs response to Jim. (towards the end of the video)

One details my installation of V-Berth hatches and foam removal.

Enjoy.

Merry Christmas to Everyone.

R/
John

 

[thataway]

For reference here is the link to the U Tube videos

I wonder if the small amount of moisture in the foam is from the anchor locker or the brass strip--that is where most of this comes. Also shows again, the "closed cell foam" really does absorb water.

Also not as much foam was forward as in many boats. It is not required by law in a 22' boat, but many are chock full of foam--yours was easier to clean out. I guess you gives you one plus....

It is interesting where your base stops forward. It may have varied from year to year. I would leave it alone.

The other interesting issue is the channels of water in between good and well adhered blocks of balsa core. I am guessing that it worked its way thru kerfs in the blocks and / or places where the blocks were not fully touching, and a small channel was left. The free thaw cycles probably expanded these channels.

Did you keep a record of the moisture readings. I have suggested that graph paper be used and the moisture readings can then be co-related to the areas where there is core damage.

Is the plan to finish the cabin sole, before you tackle the cockpit area?
I agree that when the floor goes back in it should be tabbed in with glass. Not directly related, but when we put the new cockpit floor in the 2003 C Dory 25, we used a roller and resin thickened with cabosil to give it the non skid, rather than trying to reproduce the factory non skid.

As always wonderful videos and explanations.

 

[clayhubler]

John,
Glad you got some more time to work on the boat.
Thanks for posting those videos on the hatches, I am also about to cut into that area to inspect the foam. I know that my brass rub strip and a bunch of the screws are loose and I am wondering if water is able to get in there.
I am surprised to see that the area where you put the round hatch was cored also.

Correct me if I am wrong, but at this time you still don't know where the bulk of the water got into the coring? Only the screws in the water tank compartment?

 

[hardee]

I just dropped a couple more videos.

One that covers a little detail about the raised deck to give a visual to Bobs response to Jim. (towards the end of the video)

One details my installation of V-Berth hatches and foam removal.

Enjoy.

Merry Christmas to Everyone.

R/
John

WOW, John, Nice videos.

Bob, thanks for the link.

Harvey
SleepyC :moon

 

[Brewkid]

Bob,

Thanks for adding the link! I'm going to try this "reply with quote" thing. If I botch it, the responses are below!

I wonder if the small amount of moisture in the foam is from the anchor locker or the brass strip--that is where most of this comes. Also shows again, the "closed cell foam" really does absorb water.

-Maybe is the best answer I have here. I have pulled and re-bedded the brass strip but when it was out it showed no indication of push through..The anchor locker is dry at the moment but who knows what the water could do?

Also not as much foam was forward as in many boats. It is not required by law in a 22' boat, but many are chock full of foam--yours was easier to clean out. I guess you gives you one plus....

-I'm actually pretty happy to not fight the great foam battle!! The reason I went with cam hatches is to still try and keep a water tight'ish compartment.

It is interesting where your base stops forward. It may have varied from year to year. I would leave it alone.

-I'm with you! I'll see if my OCD lets me leave it alone though...

The other interesting issue is the channels of water in between good and well adhered blocks of balsa core. I am guessing that it worked its way thru kerfs in the blocks and / or places where the blocks were not fully touching, and a small channel was left. The free thaw cycles probably expanded these channels.

-Had to have...I really can't wait to see what the back deck is hiding. I think that's my culprit like you've stated already.

Did you keep a record of the moisture readings. I have suggested that graph paper be used and the moisture readings can then be co-related to the areas where there is core damage.

-I didn't.. But I may for under the back deck.

Is the plan to finish the cabin sole, before you tackle the cockpit area?
I agree that when the floor goes back in it should be tabbed in with glass. Not directly related, but when we put the new cockpit floor in the 2003 C Dory 25, we used a roller and resin thickened with cabosil to give it the non skid, rather than trying to reproduce the factory non skid.

- Yes. Unfortunately time is not on my side and I will have to break for a while to travel for work. I'm going to keep prepping the cabin as best I can, then when I return knock out the cabin sole, then cut the back deck.

As always wonderful videos and explanations.

-Thanks!

R/
John
Scallywag

 

[Brewkid]

WOW, John, Nice videos.

Bob, thanks for the link.

Harvey
SleepyC Moon

Thanks!

R/
John
Scallywag

 

[Brewkid]

John,
Glad you got some more time to work on the boat.
Thanks for posting those videos on the hatches, I am also about to cut into that area to inspect the foam. I know that my brass rub strip and a bunch of the screws are loose and I am wondering if water is able to get in there.
I am surprised to see that the area where you put the round hatch was cored also.

Clay, Thanks! The brass strip screws from my observation have not penetrated the hull so I don't think they're a problem. As far as the coring, it looks like everything built up in the v-berth got some coring for strength. Hopefully your foam pulling party will go as easy as mine went!

Correct me if I am wrong, but at this time you still don't know where the bulk of the water got into the coring? Only the screws in the water tank compartment?

That's correct. Leaning towards migration from under the back deck and those 2 water tank screws wicking in condensation water from the tank.

Hope that moisture meter got in and she's dry as a bone for you!

R/
John
Scallywag

 

[Nainu]

Watched your last video. Have to say you are keeping the proper attitude. While time consuming and not particularly cheap, I have always found working with fiberglass and epoxy or standard resin to be very forgiving and relatively easy for do at home projects. Keep up the positive attitude and this will be an adventure.

What are you going to replace the balsa with? If the majority of the back deck is bad, I think I might do so research and see if replacing everything with Divinycell might not be the best option. Would be kind of pricy, and not sure if they make 1" with a kerf. Don't think you could or would want to bend it to shape. Seem to recall they made a 1/2" with a kerf and it is relatively flexible in that thickness anyway. Divinycell is closed cell and as long as it doesn't break down (fracture from flexing possibly), it shouldn't absorb any water ever. Maybe someone more knowledgeable than I can comment of the benefits of balsa over foam core, but I have always pondered the reasoning for the choice of balsa.

 

[thataway]

I have always pondered the reasoning for the choice of balsa.

I have written on this subject in prior threads. It is often difficult to find subjects in C Brat search engine. This quote from Boat Design Net sums it up pretty well. None of these take into account freeze thaw cycles, which accelerate the damage once there is water intrusion or delamination.

Balsa (end grain) is much stronger in compression and sheer than any of the foams. To achieve similar rigidity to a balsa core in a panel using a foam core will require a thicker core, and /or thicker glass laminates. The results are that a balsa cored panel can be lighter for a given stiffness than a foam cored one

Balsa is a great core material as long as it is done properly and does not have water intrusion.

As part of an experiment in developing instrumentation for core investigations, we cut sections out of boats to be scrapped because of hurricane damage. We found some balsa cores which were 40 years old and as intact as the day the boat was laminated. We have seen recent foam cored boats fall apart:

A couple of quotes from David Pascoe (Yacht Survey):

Once ply separation occurs, the impacts of hull against water creates hundreds of pounds of hydraulic water pressure within the laminate. The pressure is so strong that it will erode the plastic and shred the glass fibers..... A hull laminate that has been reduced to a slurry of plastic particles shreds of glass fibers, much like the way the Colorado river carved out the Grand Canyon.....People usually think that a balsa cored bottom would be far worse because of the wood's ability to absorb water. So far, the evidence at hand does not support that idea. Foam, because it is much softer, and not at all fibrous, breaks down much faster under hydraulic pressure. In fact, in all the test borings taken on this boat, the balsa itself was yet to break down. The actual failure occurred because the cored bottom panels were not properly terminated at the keel.

From Practical sailor:

There is nothing inherently wrong with core construction when it is done right. Over the years, however, Practical Sailor has seen a variety of core failures resulting in costly repair. There are five common types of failure: poor workmanship, excess flex (poor engineering), point loading, bad chemistry, and water intrusion. Each of these results in the loss of connectivity between the inner and outer skins, much like losing the span connecting the top and bottom of an I-beam. The result is a massive drop in stiffness and increased flex, and if left unattended, this can result in the critical failure of the component

From Yacht Survey this is a one year old Bertram sport fisher with total foam core failure: Sure it was bad engineering and glass lay up



I'll agree that for me working with fiberglass on small projects is fun and easy. But when you get to the scale of building a boat it is a different story. (We built a 38 foot sailboat in 2 years from start to sailing with finished interior). Professional and cautious workers use full body protection--usually tyvek suits, along with positive ventilation from external source. Although I have been working with fiberglas since about 1952, almost 70 years, I have never developed an allergy to any of the resins. However I cared for one of the fiberglass boat pioneers who died from a blood dyscrasia working daily with resins for over 25 years. Similar conditions have been reported in long term exposure to the various chemicals found in resins. That is the reason standards for protection have been put in place for professional glass workers.

 

[Brewkid]

In my search for core replacement I found this.
https://www.carbon-core.com/applications/marine/

Balsawood performs exceptionally well in static laboratory tests. The perpendicular end grains form a structure not unlike a miniature honeycomb, achieving a maximum compressive strength as high as any core material available. The high compression values contribute significantly to the stiffness of balsa-built sandwich panels. In a fire, balsa performs well, since it retains its structural load-carrying ability as it burns for a much longer period than foams do. While balsawood also exhibits exceptional shear values, the values typically presented are based on laboratory tests featuring a 0.25-inch thick panel, where balsa is at its peak in shear values. Shear values, however, are significantly reduced as panel thickness is increased.

Another weakness of balsa is its lack of impact tolerance. Specifically, its high compression stiffness causes impacts to be readily transmitted from the outside to the inside skin. One result is that the end grains are easily split, thus provoking delamination of the inside skin, which can often go undetected. Condensation can collect in the void created between the inner skin and the core and eventually result in severe water damage to the core itself. Even if the damage remains localized, repeated impact in the same area can eventually result in a catastrophic failure of the sandwich structure. Due to the low elongation of balsa, particular care must be given to the shear transfer bonding layers on each side of the core, ensuring that a low-modulus transition layer is used to “bed” the core. Timing is critical, since the core must be positioned and, preferably, vacuum bagged before this layer cures beyond gel point.

My plan as of now is replacing the Balsa with Balsa. A lot of research across the web has lead me to this point even with comment like above. I haven't pulled the trigger yet, but I'm close....

Love to hear from someone who used a different core and lived to tell about it!!

R/
John
Scallywag

 

[thataway]

Another weakness of balsa is its lack of impact tolerance. Specifically, its high compression stiffness causes impacts to be readily transmitted from the outside to the inside skin. One result is that the end grains are easily split, thus provoking delamination of the inside skin, which can often go undetected.

True, but it is also dependent on the amount of glass both inside and outside. I can show you some hull sides which were cored with foam. The foam compressed, leaving a very visible dent in the hull, just form a hard piling strike. The repair becomes a problem: do you pull the core, and replace it, or just put filler and then a couple of layers of glass over it, then fair and gelcoat?

We were racing to windward in about 50 knots of breeze, making 8 knots into 10 or so foot seas, so a lot of pounding. The boat had a 2 1/2" thick balsa planked core. The outside glass was about 3/8" the inside about 1/4". At sometime during the night we hit a container, and impacted a corner into the outer skin. The 3/8 glass was toast, the core was impacted, but still fair other wise. The area of impact was a about a square foot. The delimitation inside was about 20 sq feet., but no water intrusion. Had this been a conventional fiberglass hull the boat would have been holed, and most likely sunk--off the coast of Mexico. So there is a good reason to look upon this feature of the balsa to transmit shock as a plus. That is if you recognize that there has been damage.

Probably a good reason to regularly check out boat's floors...

 

[Ehauge]

Quick question on inspection port placement in the bow. Has anyone else placed the port forward of the head? The video I watched in this thread showed the port right under the head. I thought it would be good to place it further forward.

 

[Brewkid]

Not sure if you're talking about the inspection hatch I installed, or the smaller plug that's used to fill in the foam. The plug sits right under where my porta potty sits. The inspection hatch is on the raised surface just as you enter the berth. The lower area on a 22 cruiser has so little room between the hull and the plug, I don't think a plate there would be of much use.

Sorry, not sure if I answered your question or not!

R/
John
Scallywag

 

[thataway]

Quick question on inspection port placement in the bow. Has anyone else placed the port forward of the head? The video I watched in this thread showed the port right under the head. I thought it would be good to place it further forward.

I have seen several boats with a floor plate as far aft as possible in the V Bunk floor molding. It is in that place in my 25. Further aft is deeper than more forward, and where water might accumulate. (None ever seen in my 25). The goal is to check for, and remove any water which might get under the floor forward.

 

[colbysmith]

Hi Bob,
C-Traveler does not have any ports or holes in that area just forward of the cabin in the middle of the V-Berth. I've debated putting an 6" inspection plate, or one of my old lazarette covers that I replaced on Midnight, into that area. Would there be any room to store charts in that area? (Hatch cover would be perfect for that). Or would it be wise to put the 6" inspection plate just to have access for inspection? Colby

 

[thataway]

Colby,
My boat has all of the foam removed, if there was any to begin with. There is not much room under the floor. Forward of the floor molded area under the platform, I put spare anchor and anchor rodes to the sides, the Li batteries and inverter. Not a lot of area, but good place to store clothes not used regularly. I would put them in a water resistant duffle, just in case. But in my boat, it has been bone dry.

 

[colbysmith]

If you are talking about that area up under the mattress, I don't have any foam in that area either, and it doesn't look like there ever was. I've got storage on both sides and then in that middle part. A lot more than I did in the 22. And it's all stayed dry. I also keep a spare anchor and some props and maintenance supplies, along with my downriggers in that center forward compartment. Actually the downriggers get moved around, depending on if I'm thinking about using them or not. It's kind of a pain to get into that compartment, under the mattres. In the V-berth side compartments I keep mostly "household & grocery" supplies. I don't think there is any core in the area, but rather just the fiberglass. Except maybe under the very bottom. Not sure why they built up that center area with a void. Perhaps there is some foam under there.