Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

[dwedeking2]

When you manufacture a product that will be replicated you look for solutions that are economical and provide a "best practices" safety factor. A boat manufacturer may be turning out 200 units a year that need to last until the warranty period is over.

I recently rebuilt the area in the bow that holds cleats and my windlass. I need 0% percent failure and have only the 1 to worry about. I paid through the nose for a synthetic core that will never need to be redone. I over built with glass. My boat maybe sunk by a nuclear weapon and the windlass will be attached to the deck. Lol

Stupid to do that if you owned a business

[thinwater]

Originally Posted by valhalla360

Shouldn't be attaching hardware thru cored sections at all.

Foam can work but as mentioned, takes a thicker cross section to get the same strength and stiffness. Plus it's harder to get good adhesion between the layers.

Keep it dry and balsa is a great material.

Put simply... I didn't do it, the builder did, several boats. You are, of course, correct and I agree.


Fender washers are still a pet peeve. Every core leak I've ever fixed had a bent fender washer involved.

[GordMay]

S/S Fender/Penny washers are available in "Extra Thick" (1/8") versions:
ie ➥ https://www.boltdepot.com/Fender_was...tra_thick.aspx

[JDanielBryant]

Balsa is selected for it's compressional strength. End-grain balsa has a compressional strength of about 6 ksi, which is about 3 times that closed cell polymerics of comparable density. I researched these products extensively about 10 years ago as I had invented and patented a closed cell aluminum foam (I'm a material scientist and worked for Alcoa at the time) that I thought would be a good replacement as core material for marine and architectural panels. Best of all, it didn't burn so it would meet all international fire codes. Unfortunately it cost more than balsa or polymeric cores so it was not adopted. The polymeric core (LDPE) was cheaper so it continued to be used. Fast forward 7 years and you know the result: 72 dead in the Grenfell Tower fire in West London - LDPE burns like gasoline.

[a64pilot]

Yes, but if even the thinner ones are bending, it screams that the material is compressing, and that of course means that you have lost the torque and obviously damaged the underlining structure.
Don’t ever think a bending washer is acceptable, and going thicker so the substrate crushes without bending the washer isn’t a fix.

[MoorOrLess]

Unfortunately end grain balsa gets a bad rap because of incorrect install. If correctly installed, even if a hole was later drilled through the deck and not sealed, the water ingress would only be 1” x 1/2”. Each piece of balsa should be sealed. The problem is when it is not properly installed and the hack of a builder just bonds the sheets to the glass.
I use to build 40’ balsa cored boats. It takes a more time, but is easy to do correctly.
The balsa is a great thermal and acoustic insulator.

[Chotu]

Originally Posted by MoorOrLess

Unfortunately end grain balsa gets a bad rap because of incorrect install. If correctly installed, even if a hole was later drilled through the deck and not sealed, the water ingress would only be 1” x 1/2”. Each piece of balsa should be sealed. The problem is when it is not properly installed and the hack of a builder just bonds the sheets to the glass.
I use to build 40’ balsa cored boats. It takes a more time, but is easy to do correctly.
The balsa is a great thermal and acoustic insulator.

How do you best install the balsa in such a way that the space between the blocks is sealed off?

[MoorOrLess]

We added two fillers to the polyester resin, (silica and q-cells) in 70/30 ratio. Silica gave the strength and the q-cells the workability. Add until fillers until it is between honey to peanut consistency. Apply to the glass so that it was about 3-4mm thick. Starting at the bottom if laying vertical place the bottom row into the paste while holding the rest of the panel out. Slowly start pressing row by row against the paste while at the same time use a roller to press the balsa against the hull/job. If using a colour changing resin, the resin paste will be easily seen surrounding each of the balsa pieces. Work your way up, if there use an area which doesn’t the balsa completely surrounded, peel back and apply a little more paste. The fillers increase your working time.

[s/v Jedi]

Originally Posted by Chotu

How do you best install the balsa in such a way that the space between the blocks is sealed off?

On my boat the SCRIMP vacuum infusion process was used so that every balsa square is completely encapsulated by vinylester resin

[Chotu]

Thanks. I was curious how everyone did it. My entire hull and deck were infused in one shot so the balsa was infused with resin beyond what bagging and hand layup can do. Just like Jedi above.

I was sort of double checking that this would make discrete little isolated blocks of balsa as I had hoped and it seems like this is indeed the case.

By infusing balsa, you actually stand a good chance of having it stand up to an unprotected drill hole because it has thousands of tiny "dams" in the core to keep water localized. At least that was my theory infusing my foam hull and balsa deck. I created thousands of epoxy dams in the core.

Glad to hear it's well accepted by others.

[MoorOrLess]

Bagging and infusion is the way to go for any cored hull.
The constant/even pressure of the bagging will disperse the resin and fill between the pieces of balsa. While that method existed back when I did it, typically it was used on the larger one off vessels or large production facilities..... we were a small yard.
Some builders in the 80’s and 90’s just laid balsa using the same method as they did for foam or ply and this didn’t seal off the individual pieces.

[jimbunyard]

Originally Posted by dwedeking2

When you manufacture a product that will be replicated you look for solutions that are economical and provide a "best practices" safety factor. A boat manufacturer may be turning out 200 units a year that need to last until the warranty period is over.

I recently rebuilt the area in the bow that holds cleats and my windlass. I need 0% percent failure and have only the 1 to worry about. I paid through the nose for a synthetic core that will never need to be redone. I over built with glass. My boat maybe sunk by a nuclear weapon and the windlass will be attached to the deck. Lol

Stupid to do that if you owned a business

Hard too imagine a better indictment of un-regulated capitalism, or, if one prefers, the perils of a free market taken to it's logical conclusion. Conspicuous consumption indeed...

[a64pilot]

Originally Posted by dwedeking2

When you manufacture a product that will be replicated you look for solutions that are economical and provide a "best practices" safety factor. A boat manufacturer may be turning out 200 units a year that need to last until the warranty period is over.

I recently rebuilt the area in the bow that holds cleats and my windlass. I need 0% percent failure and have only the 1 to worry about. I paid through the nose for a synthetic core that will never need to be redone. I over built with glass. My boat maybe sunk by a nuclear weapon and the windlass will be attached to the deck. Lol

Stupid to do that if you owned a business

What you posted is why I believe at least a few boat builders went out of business, they refused to ruin their reputation and build lower quality boats, but when a consumer is faced with the fact that they can get much larger, for less money, the quality boats don’t sell.
Same for houses, people want BIG and impressive, they don’t want well built, they are in denial, or maybe the logic is they will sell before it becomes a problem?

[malbert73]

Originally Posted by a64pilot

What you posted is why I believe at least a few boat builders went out of business, they refused to ruin their reputation and build lower quality boats, but when a consumer is faced with the fact that they can get much larger, for less money, the quality boats don’t sell.
Same for houses, people want BIG and impressive, they don’t want well built, they are in denial, or maybe the logic is they will sell before it becomes a problem?

Yes the McMansion syndrome doesn’t stop in the suburbs....

[iduff]

Originally Posted by DerekKelsall

PVC foam has been available since about 1960. In 1965 I built trimaran Toria of PVC Foam and unidirectional fiber glass skins (polyester). We won RBR 1966. Sister ships are still sailing. The same year I introduced my rule to never spec. anything in the structure that can rot. - had seen the results of balsa in decks. There is no way to justify balsa in a boat structure.
Happy boating, Derek Kelsall.

Mr Kelsall is absolutely right.

I started building with Airex in 1968. Still a few years later than Mr Kelsall. Built a few hundred Airex-cored boats. Between us, there's just a bit of real world experience on display. </sarcasm>.

Back then, Airex was susceptible to heat-softening, which balsa is not. This made it somewhat useful for decks.

Foam technology has advanced to the point it is now suitable for even higher heat environments, like a deck core.

Balsa core has no place on a structure subject to any kind of impact, as it will shear from its skin far too easily. A big guy jumps down from the dock onto your balsa-cored deck? Shear delamination is quite likely. An Airex cored structure will take quite a beating without delaminating.

Any cored panel should be laminated with sufficient care that there will NOT be voids between the core and the skins, whether that's balsa or foam. Any discussion of water propagating along a core/skin delamination speaks to shoddy workmanship, and not to core material. Or maybe to misuse induced shear delamination of a balsa core panel.

Unless the builder took great care to properly lay out and laminate with a balsa core, leaving no core in areas with any hardware, and properly bonding the skins to the core, balsa is a BAD choice for marine core material. Add in the inevitable addition of hardware in cored areas, and the resulting ingress of water into the core, and you end up with mulch as the core material. All the more reason to leave balsa to the model airplane builders, and far, far away from any boat.

BTW, please, please, please DO NOT USE fender washers as backing for any hardware. Use a proper backing plate.