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Old 10-05-2019, 21:12   #76
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

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Originally Posted by wingssail View Post
It’s all well and good to use terms like, “if it is done right…” or to describe the perfect technique for laminating a cored structure. The problem is that the builders don’t always have the skilled staff and the proper techniques aren’t always followed (the foreman was an alcoholic, the floor workers had sub HS education and their last job was McDonalds and the owner was busy trying to stave off bankruptcy). So most of us are stuck with boats that weren’t built perfectly. Deal with it. Talking about the benefits of various core materials is pretty theoretical compared to the real issues of quality control.

In my case a bunch of rednecks built my boat in a dirt floor barn in New Orleans, and it still has lasted well through 40 years of very hard usage. But I found uncured polyester resin 20 years after first launch and, Ok, the balsa core deck has rotted in several places and I’ve re-cored it. Not hard to do but I have not always had access to end grain balsa so I’ve used other softwoods, such as pine, and it has held up well. Most of my highly loaded deck fittings (what isn’t highly loaded on this boat?) now have big backing plates and solid wood cores, although they weren’t that way originally. It was a bit odd to watch genoa turning blocks move around on the deck as their bolts plowed through the skins and balsa. But look at this winch (photo), it is on balsa core with a ring backing plate and it withstands over 4000bs load, often. Been there for 40 years, no rot, no issues.

The hull was cored with C-Flex (no longer used) and it has been brilliant, strong, solid, and reasonably light. (my 43’ weighs 16,000lbs and 38% of that is keel, and then there is the motor, rig, winches, etc, so the hull is pretty light, about 5000lbs). I don’t have any foam core but I have seen foam core hulls where the outer skin has come loose from the foam and the whole structure flexes. Repairing that is a big job. Also on foam cores or any core with thin skins, the outside skin can be punctured, not good. My least favorite core material is foam because it may be difficult to bond properly to the skin (quality control, remember?).

Honeycomb panels: I have used nomex honeycomb panels (surplus from Boeing, but odd shapes!) for my entire interior build out since I first discovered the stuff. Light, strong, does not rot, and good compression strength; however it has to be tabbed since fasteners don’t hold although with big fender washers you can through bolt it. The polyester skins are best for glassing, but the carbon fiber skins are quite a bit stronger.

Bottom line: there are pluses and minuses to each hull construction method, but real world is that few boats were perfectly done, and saying, “if only it is done right, there is no problem...” is a bit disingenuous, and sort of self congratulatory. Any material can be used, and if done well it will serve. If not, you can repair it. Perfect is th enemy of good.
I'm somewhat confused by several points in your post.

Obviously nothing constructed can be considered 'perfect', if only because of the transient nature of time...(haha)

In the order of your post.

Why is it 'easy' to replace balsa core, yet replacing foam core is a 'big job'?

C-flex was a kind of construction material and method invented by Seeman, if memory serves, originally for use in coating wooden shrimp boats. It consisted of solid fiberglass rods in a woven fiberglass mesh that was stapled to a 5200-covered wooden hull that was then saturated with polyester resin, which was then faired, or fiberglassed and faired. Later it was used by itself for original constructions by being stapled to an either permanent or temporary mold, in a manner similar to cold molding or strip plank building.

I've never heard of C-flex 'planks' being used as core, but if it was then you have basically a solid fiberglass structure. If you have C-flex skin over a balsa (or other) core, then you are not comparing apples to apples, because C-flex itself, unlike flexible reinforcements, is considered a structural component of the skin (at least in one direction [until saturation,when it becomes structural in all three]). And C-flex skins are generally quite a bit thicker than those made from woven reinforcements because of the 'rods' from which C-flex is made...

I've used many different brands and types of plastic foams in many different modes. When coating with resin and fabric-type reinforcements, I've had only one instance of bonding failure, and that was with PVC foam that was contaminated on it's surface.

Which is not, of course, to say that stress induced failure is impossible with PVC or any other type core, but that proper care in construction technique goes a long way towards preventing, or at least lessening such failures.

Having dealt with honeycomb panels only twice (that I can remember), the only thing I can say is that in both instances, the plastic honeycomb did not seem to adhere to the polyester skin properly. That was at least 16 years ago, so I hope 'they've' got that issue worked out by now...

Perfect is the enemy of good enough...


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Originally Posted by u4ea32 View Post
Well, of course someone who fixes boats gets called in when there are problems. I am not surprised you have seen many boats with problems.

What was the root cause of these issues? It obviously was not the balsa, as the many examples of old, dry balsa boats (such as mine) attest.

It is clear there are problems with some boats, including some expensive boats (Bertram's well documented problems that crushed that company 30 years ago).

There are also documented problems with delamination in un-cored fiberglass, especially when polyester is used. Polyester is quite porous to water vapor, so H2O molecules can migrate into any polyester laminate and then cause delamination because water does not compress, and ice expands.

There are examples of foam cored boats completely de-laminating, even those built with epoxy (no water vapor).

There are examples of metal boats being disasters, or perfectly fine and very long lived.

There are examples of wooden boats that have lasted a very long time with little problem -- those built by Gougeon are obvious examples. Yet clearly, most wooden boats do not last long.

So it is not simply the material.
To repeat myself and others.

Balsa core is a fine material, but it has a primary enemy, which is, of course, water, or more properly, water which persists long enough to enable, shall we say, negative consequences. Which makes it seem almost asinine to use it in boat construction, especially since there are now products that duplicate or exceed its' performance. Without the chance of rot-related failures...

Balsa was originally used because it was the only game in town, as competing materials became available, it was used because of it's real superior characteristics, then it's supposed superior characteristics, to now being used primarily (I think) because of its' (initial) lower cost.

As for 'root' or ultimate causes, it seems to me you have them backwards.
The ultimate cause of balsa core failure is that it is balsa, in other words, because it rots, or is more susceptible to rotting.

The proximate causes of failure are poor construction techniques, owner/operator errors, or perhaps more usually, a combination of both, which are the same for any core; indeed for almost any constructed thing.

I'm not really sure how the physical properties of water are changed by it being present in either balsa core or plastic foam. Seems to me that freezing or porosity problems would be the same, or mostly the same, regardless of core material, though the hydrophilic property of any wood, but especially balsa, would exacerbate those problems, especially when compared to the hydrophobic properties of the plastics from which foam cores are made.

The vagaries of life in the real world should put paid to any attestation of 'because my experience is 'this', therefore 'this' is 'correct' or 'the way it really is' ',

I have no doubt that yours and Wingssail's experiences are accurate, but I don't think they represent the norm. Both of your boats, by your own descriptions, seem to be custom built, or at least semi-custom built, and therefore, perhaps, out of the realm of what is more often under discussion in these pages, i.e. standard production boats.

For instance, in both of your boats, are either of you aware of what grade balsa core was used? Balsa, like plastics, is available in different densities, and those differences change its' water (and resin) absorption, as well as its' tensile and compression strengths; this crucial difference is often overlooked, essentially mooting any comparisons...
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Old 10-05-2019, 21:24   #77
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

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For instance, in both of your boats, are either of you aware of what grade balsa core was used? Balsa, like plastics, is available in different densities, and those differences change its' water (and resin) absorption, as well as its' tensile and compression strengths, and this crucial difference is often overlooked, essentially mooting any comparisons...
That's interesting, and I was not aware of this aspect of balsa coring. Could you amplify on the subject a bit, please? What grades are typically used in what applications? Ie, is a different grade used in decks (where compression loads might be higher) than hulls or bulkheads? And is t here a cost differential between grades of balsa?

Our previous boat, built by Palmer Johnson, had air-x coring in the hull and balsa in the deck. We had minor delamination in part of the deck (without water intrusion) and minor rotting in way of the chainplate penetration. The hull had no coring issues when we sold the boat at age 30 years. I'll admit, though, that the skin thicknesses were hideously overbuilt by modern standards, and that may have contributed to its longevity!

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Old 10-05-2019, 22:16   #78
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

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Originally Posted by Jim Cate View Post
That's interesting, and I was not aware of this aspect of balsa coring. Could you amplify on the subject a bit, please? What grades are typically used in what applications? Ie, is a different grade used in decks (where compression loads might be higher) than hulls or bulkheads? And is t here a cost differential between grades of balsa?

Our previous boat, built by Palmer Johnson, had air-x coring in the hull and balsa in the deck. We had minor delamination in part of the deck (without water intrusion) and minor rotting in way of the chainplate penetration.

Jim
I can't, because I don't use it and I'm sure that major manufacturers specify those characteristics to their own idiosyncratic needs. I'm quite sure there is a price difference in densities, if only from (going way back) remembering the price difference relative to the hardness (for me it was quantified by my ability, or not, to cut it with a variously sharp exacto knife); the stuff I could cut easily was half as expensive as the 'good (spar quality) stuff'...

A quick search yields several different densities from 109 to 335 lbs/cu m.

A data sheet for one grade of coring supplied by Baltek, probably one or the largest manufacturers, is here

https://www.3accorematerials.com/upl...-SB-E_1106.pdf

Their website is here

https://www.3accorematerials.com/en/...s/baltek-balsa

Quote:
...The hull had no coring issues when we sold the boat at age 30 years. I'll admit, though, that the skin thicknesses were hideously overbuilt by modern standards, and that may have contributed to its longevity!
I think that nicely sums up the underlying consensus...
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Old 11-05-2019, 00:26   #79
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

I have personally seen whole sides of boats with their skin ripped off trying to take out all the rotten balsa core. For me, it is a risk I would not want to take. Making sure a owner never penetrates a sealed core area is highly unlikely, and that's not including any manufacturing flaws that no one would know about until its too late. There is all kinds of ways to stiffen a hull or deck than trusting balsa core to do it. Now since we have lower cost carbon fiber and better foam core material, there is better options.
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Old 11-05-2019, 02:09   #80
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

Everything you need to know about this subject is right in this chart containing all core materials.

Look at the "Compressive Strength" column and see what material is better for compression. WAY better. That's why it's in my deck. It's a far superior material.


https://www.corecomposites.com/filea...omparison2.pdf

Looking at that chart, given the size backing plates I used to spread the load of my deck cleats for instance, I could probably lift my boat up by a deck cleat. (It's a catamaran). TTY that with foam and it's going to crush and deform because it doesn't have the compressive strength.

Anyone can build a piece of junk in any core material. You can hand laminate foam or balsa poorly leading to delamination of either. In my case, all air was removed under vacuum inside a bag and then replaced with epoxy resin. I could have used sandwich bread for a core and it's not going anywhere. Because all air was evacuated and replaced with epoxy.

Foam is no better than balsa, just different. Right tools for the right job. When you need compressive strength, such as in a deck, nothing beats balsa. When you need ability of a core to spring back after moderate impacts, foam is your choice.

None is better than the other, they just have different properties suited for different uses.

Imagined faulty construction and boat owner misuse are not valid arguments. Don't buy poorly made boats and don't be an idiot and all cores can then be judged on their physical properties. Properties which are suitable to the use of the core, such as balsa being the absolute best core for a deck, where compresion and sheer are most important.

My boat is all foam. The hull, the dagger boards, the structural bulkheads, the connectives, the steps, the rudders, everything. Except the deck. I used the absolute best materials money can buy on the boat. And balsa is the best material money can buy when you are using it in a place where there are high loads on the laminate.

Right tools (materials) for the right job.
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Old 11-05-2019, 05:11   #81
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

There are some better much pricier foams that are not on this chart, including Rohacell for example.
Compressive strength is not everything in our deck loading scenarios either. When bending a cored structure there are significant shear loads in the core. That number is certainly a more useful comparison for pure bending.
Iím not saying balsa isnít the best bang for the buck when initially built.
And I wonít say foam doesnít fail.
I have owned dry core balsa hulls. I have owned dry foam core hulls. Wood hulls. Pure glass hulls. Each has pluses and minuses.
Some are sensitivity to environmental factors, sensitivity to neglect, sensitivity to physical abuse. Structural weight. The list goes on.
There is no best material for all marine applications.
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Old 11-05-2019, 06:42   #82
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

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.
There is no best material for all marine applications.
This. Exactly. Each core has its properties and using the best one for the job is the way to go.
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Old 11-05-2019, 07:16   #83
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

The problem I see with cored areas is not so much the material, but BOTH the end user and the manufacturer. In THEORY these products are fine. In REALITY they are installed in the hull by a guy who is the bottom of the totem pole at the boat maker. He's got mask, ventilator and goggles that he can't see well through, he's sticky all over, is high on fumes and that is his life for 8-12 hours a day. Thinking that he is going to get everything right, including saturating the coring (balsa or foam) with resin so it isn't so much like a sponge, or doesn't degrade just from vibration is a fools game. Much less relying on him to notice that the hardener injector is actually working properly and not over catalyzing or under catalyzing is very iffy. "It's end of day, and if I can just get this sprayed and finished without having to change that barrel my life will be easier".
It's like asking a drunk in a space suit to walk the white line perfectly.
There's a huge gap between material science possibility and real world ability.
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Old 11-05-2019, 07:42   #84
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

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This. Exactly. Each core has its properties and using the best one for the job is the way to go.
Including the competence and will to do the job right.
Most of the problems with delamination issues in the past were fails in bonding in mould laminated boats. Either failed infusion or no vacuum bagging at all were the most common ones. Such events have been unknown for one-offs. Wet and rotted balsa cores, besides the previous, are caused also of negligence in installation of hardware on decks without any responsibility or professionalism. The weight of the core has nothing do with any of it.

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Old 11-05-2019, 11:28   #85
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Re: Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

My 1980 Cal 31 was constructed with Klegecell foam in the deck. I know I have water intrusion but the decks are still solid. Given that an old boat, which might have had several owners, items added to the deck or just wear and tear on existing penetrations, my experience says the foam is a great option. Agree that Balsa has great qualities but can be compromised if penetrations are not meticulously constructed and maintained (hard to turn back the clock if a PO didn't do that). Really sad to see an otherwise great boat with spongy decks.
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