Inexpensive hull construction materials

[waikikin]

I don't think jeepy is overly familiar with the idea that you catch more flies with honey, than you do with vinegar !
Nevertheless, I wish a happy Christmas to all !

Great point on the season,
Compliments of the season to All & a prosperous New Year, have a good one.
All the best from Jeff.

 

[fpjeepy05]

No general term here. Use the correct term if you pretend to know what you are talking about. "Modulus of elasticity in compression and elongation at failure" is nowhere to be used to be used when defining core property for use. Quit pulling our leg.

What physical properties of the materials do you use?

A poly putty is typically very weak and brittle.

Compared to PVC foam?

If the core fails by elongation, either it is more brittle than glass, or the laminates are made of rubber.

Think of a sandwich core construction like a deck of cards. The top and bottom card being the laminate and the other 50 cards a core. When you flex the deck the shear forces cause the cards to slide against one another. If you put a weak glue, flour and water, on the cards and let it dry, then flex the deck. The "core" will fail in shear. The flour-water will not be able to elongate much before it breaks. Now do the same thing with bubblegum between the cards. The higher elongation will allow the cards to flex without breaking the bond.
San foams are more expensive than Cross-link PVC foams which are more expensive than normal PVC foams. The more expensive the foam, the higher the elongation at failure.

In the end it's all pretty simple even if the OP does not want to see it. If one uses enough filler material to strech poly resin enough to make a price difference the core will be unsuitable for the task.

Coremat is a filler material used to stretch poly resin that is commonly used as a core.

Hi fpjeepy,
There's an observation... 8 negative words highlighted. Discussions should seek common ground but a level of respect needs be applied as often once all the information distilled the answers sought might be revealed. There's a big difference between being dictatorial and collegiate & I know who achieves the greater success and respect. Open forum, bring some, if you already have the answers you seek share them or not.
Regards from Jeff.

Jeff, I don't have the answers, that is why I am on here. But if I know that someone is spreading information that is not true I feel a moral obligation to correct them.

Merry Christmas to all!

 

[TANSL]

But if I know that someone is spreading information that is not true I feel a moral obligation to correct them.

I totally agree with you and I encourage you to keep doing it.

 

[DogCavalry]

fpj - Are you talking only about the mold or the boat part? For the mold, we recycle the empty paper tube the fiberglass is rolled. We cut it half and use as stiffeners. No need to buy PVC.

Not screwing around here!

 

[Rumars]

Coremat is a filler material used to stretch poly resin that is commonly used as a core.

I would not call coremat "filler material", but you can learn a lot from it. Yes it uses microballoons to displace resin, achieving about 50% reduction over CSM. But it also uses fibers, not only to fix the balloons in space and provide an even thickness, but to reinforce the otherways very brittle mix. There is a reason it's not marketed as a core, but a bulking agent. Laminates containing it are not considered sandwich as far as I know.
As you have discovered it is more expensive then poly/CSM even if it reduces resin use by 50%.
You can not really make a similar material at home cheaper, just like you can't make foam sheets.
I will stand by my statement that you can not make something cheaper with the same properties until proven wrong. Even laminates containing coremat don't have the same physical properties as same thickness all glass ones.

 

[gonzo]

Think of a sandwich core construction like a deck of cards. The top and bottom card being the laminate and the other 50 cards a core. When you flex the deck the shear forces cause the cards to slide against one another. If you put a weak glue, flour and water, on the cards and let it dry, then flex the deck. The "core" will fail in shear. The flour-water will not be able to elongate much before it breaks. Now do the same thing with bubblegum between the cards. The higher elongation will allow the cards to flex without breaking the bond.
San foams are more expensive than Cross-link PVC foams which are more expensive than normal PVC foams. The more expensive the foam, the higher the elongation at failure.

1-A deck of card can be compared to a laminated wooden beam, where the material is homogeneous. A foam sandwich construction is completely different. The materials do not have the same physical characteristics. Further, the foam core is not composed of laminations that slide against each other. Another difference, is that the skins are composed of a resin matrix that is adhered to the core with the same resin; the bond is not weaker like flour.
2- The deck of cards can not fail is shear as you explain it, since the cards slide between each other. No shear exists.
3-Flour or bubblegum will have very little difference on the behavior of a deck of cards being bent. Read above.
4-The cost of foam is not directly related to its elongation failure value. The physical characteristics are engineered for particular applications.
In short, none of your claims have any basis in science or technology.

 

[ondarvr]

You brought up core mat....again.

Have you every used it, or know what it’s used for?

Core mat (and similar products) tends to be used in applications where the laminate is strong enough without it, the laminate just needs to appear stiffer. It’s not used to add strength without weight as a typical core would be.

Have you every held a block of polyester resin in your hand, then dropped it?

The impact resistance of a high resin content composite is low. It will tend to shatter when flexed, or receives an impact. This isn’t something that’s desirable in a core.

Foam cores tend to not fail in the same way, the better the foam, the more abuse it will take.

Do you have much of a background in composites? I ask that because at times you appear to have some knowledge, but in other aspects you seem to understand very little about how different materials work when used in combination with others.

 

[fpjeepy05]

I would not call coremat "filler material", but you can learn a lot from it. Yes it uses microballoons to displace resin, achieving about 50% reduction over CSM. But it also uses fibers, not only to fix the balloons in space and provide an even thickness, but to reinforce the otherways very brittle mix. There is a reason it's not marketed as a core, but a bulking agent. Laminates containing it are not considered sandwich as far as I know.
As you have discovered it is more expensive then poly/CSM even if it reduces resin use by 50%.

I don't care if it is called a core or not. It reduces the density and/or strength of the inner area and makes the overall structure thicker and in turn stiffer. The same that a core does.

You can not really make a similar material at home cheaper, just like you can't make foam sheets.
I will stand by my statement that you can not make something cheaper with the same properties until proven wrong.

And you have the right to your opinion.

1-A deck of card can be compared to a laminated wooden beam, where the material is homogeneous. A foam sandwich construction is completely different. The materials do not have the same physical characteristics. Further, the foam core is not composed of laminations that slide against each other. Another difference is that the skins are composed of a resin matrix that is adhered to the core with the same resin; the bond is not weaker like flour.

The purpose of the deck of cards analogy was to help explain to people that don't understand shear forces in a core material.

2- The deck of cards can not fail is shear as you explain it, since the cards slide between each other. No shear exists.

Sure. I'll give you that one.

3-Flour or bubblegum will have very little difference on the behavior of a deck of cards being bent. Read above.

Try gluing a deck of card together with flour and water. It will be much stiffer than a deck of cards unglued. And when you bend it you will hear the glue failing. The force the glue is experiencing is shear.

4-The cost of foam is not directly related to its elongation failure value. The physical characteristics are engineered for particular applications.

I didn't do a full study of this. But
Corecell M80 (SAN foam) 1"4x8 (Elongation at rupture 53%) ~$400
Diab H80 (Cross-link PVC) 1" 4x8 (Elongation at rupture 20%)~ $300
Chinese PVC (PVC / who knows) 1" 4x8 (Elongation at rupture 10%) ~$100

A bad core can not elongate in shear without rupturing... And this doesn't necessitate the core to be "more brittle than glass, or the laminates are made of rubber."

 

[fpjeepy05]

You brought up core mat....again.

Have you every used it, or know what it’s used for?

Core mat (and similar products) tends to be used in applications where the laminate is strong enough without it, the laminate just needs to appear stiffer. It’s not used to add strength without weight as a typical core would be.

Yes, I have. I work in the industry. We use Spheretex for purchasing reasons. If you would like to learn more about it call Jack Lugus of Carbon Core.

Have you ever designed a laminate for marine use? A boat hull? Failure mode is bending. Gelcoat cracks before laminates fail and spider cracks in Gelcoat is a failure. Stiffness is the name of the game. Bulking agents and cores add thickness and add stiffness.

Have you every held a block of polyester resin in your hand, then dropped it?

The impact resistance of a high resin content composite is low. It will tend to shatter when flexed, or receives an impact. This isn’t something that’s desirable in a core.

Foam cores tend to not fail in the same way, the better the foam, the more abuse it will take.

Do you have much of a background in composites? I ask that because at times you appear to have some knowledge, but in other aspects you seem to understand very little about how different materials work when used in combination with others.

No, every time I've ever mixed resin I mix the perfect amount and have never had any left in the bucket. ???

1-5% milled glass fiber by weight will solve all those problems and adds pennies. You should know this ondarvr...

 

[ondarvr]

This is really getting crazy, I’m not sure where the discussion goes from here.

We make fiberfilled polyester putties, I know the price, it’s not cost effective, nor does it have good physical properties as a core.

I do multi-day composite schools and training seminars with the large distributors, the fabric, core, catalyst, resin, gel coat, mold release, filler suppliers and others are there to help customers choose the correct products and methods for building boats and just about every other thing made from composites.

We also do onsite production audits for large customers to help them be more efficient in building whatever it is they produce. I’ve also done this internationally.

I’ve known these people and have done training with them for decades. We vacation together, our families are friends.

So, if my information is bad, or you consider me uninformed, then the entire industry on every continent is.

Again, I’m not being negative, I’m only giving you information aquired over decades of manufacturers and suppliers looking at doing exactly what you’re talking about.

If you have some ideas that are better or different, then please, by all means, bring them up and explain why you feel they will work. I would love to be part of that conversation.

To this point you haven’t presented any details about anything, just saying that you “know” some undiscovered or undisclosed filler “will” work in polyester resin as a very low cost and strong core.

 

[ondarvr]

I forgot to add this earlier.

I’ve been involved in developing sprayable polyester cores, and then did tech service and training for the customers to use them in production.

These cores weren’t considered structural at all, they were to help block print from structural cores and stiffen thin panels.

I’ve done similar work with pumpable polyester putties and cores.

Even when made as low cost and easy to apply as possible, they weren’t “cheap” to use.

The cost can vary, but doubling the cost of the resin can be exceeded easily.

Then add the cost of the equipment used to apply them.

 

[gonzo]

A bad core can not elongate in shear without rupturing.

There isn't any material that won't elongate. Unless of course it is unobtanium sulfate.
Also, an analogy of a deck of cards to a foam core is completely wrong. It could be used as comparison to a laminated wooden beam though. Remember that you are dealing with a lot of engineers and designers, so take the time to use terminology and analogies correctly. Otherwise, you will be called on your errors.
Another mistake is to look at elongation at rupture as the only indication that one core is better than another. For example, you need to consider how much stress is necessary to attain that elongation.
You started this thread asking about the cheapest material, and still insist that wood is not it. However, all your alternatives are more expensive. When nobody agrees with you, your answers turn to tantrums. Prove you are wrong by posting the price and physical characteristics of the material you claim is cheaper and better. Getting supplies for free will only count if they get compared to the free wood you can get by cutting a tree.

 

[ondarvr]

Ok, I have one more thing to add.

I recently did a stint as a plant manager at the largest manufacturer of cored panels in North America, they’ve been making panels for around 50 years.

We made everything from low cost down and dirty stuff, to high end Balistic projects for the military, and everything in between.

The lowest cost panels used wood as the core, and believe me, if there was something cheaper we would have used it.

 

[waikikin]

No, every time I've ever mixed resin I mix the perfect amount and have never had any left in the bucket. ???

Nice one FPJ .... I'll make that my New Years resolution

Jeff

 

[fallguy]

It does matter if you don't want wet, rotting paper and associated mold perpetually in your bilge.

Plywood will be the first choice, what would be the second?

I agree that a chopper gun may be the most well-established solution, but there has to be other outside the box solutions that are comparable. Recycled plastics sell for cents per pound polyester resin has compressive and shear strengths 10x that required for a core material. Do they make a hopper gun that shoots plastic pellets? Something like the popcorn ceiling guns?

This post from long ago in the thread was a grand hope. I did not comment because I hate to rain on hope.

The trouble with plastic is that plastic is a generic term for many arrangements of chemicals. And plastics are not friendly to each other. I worked in plastics for a few years and we couldn't even recycle our own product back into itself easily, fully, well. We were able to use our recycled plastic in the core, ironically. The problem was the inks used messed with the colors and the extrusion really would only cooperate to a degree of reintroduction of about 10%. When we put a new extruder online; initial setup falldown was massive and we had to rent an old warehouse to store it all. Basically, miles of plastic waiting to go back into core at a rate of 10% of about 40% of the total or 4% reintroduction only. I did some analysis of how long it would take and to see if it was cheaper to rent or dispose. It was cheaper to dispose, but the company actually wanted to do the right thing. And we used it as a chip for the rental rate for an unised building.

Core materials need to be consistent is my point I suppose. You can't just mix up a bunch of plastics and get them to process easily. The process of refining recyclables is its own process.

The Andersen Window Corp wanted to reduce vinyl/wood wastes. So they ground it all up and ran it through density separators. Giant vibrating tables that operate at a certain frequency so the grindings go into different conveyors and hoppers. The process was good, but the vinyl still had bits of wood on it. So, they ground it again and made a wood/vinyl material that is actually wood and pvc combined. Yeah, I said it.

Anyhow, fpj is probably feeling a little beat down by the forum, so I thought I'd throw him a bone.

I am not sure how the wood and pvc would behave as a core, but lighter with lower absorption of water rates, etc. than wood alone.

But you asked for the second cheapest core and I would say wood combined with recycled plastic/vinyl would probably be it.

The reason we don't have it is the research required to refine the recyclables and then grind it all into a core and then determine a way to extrude it is certainly not easy stuff. And the capital costs are way high for it. There is probably quite a bit of research going on now with the plastics glut. One would hope.