Are Cats Made from Duflex Panel Kits Strong ?

[beiland]

Originally Posted by 44'cruisingcat

The article doesn't only refer to collision damage. It also shows foam cores which have been destroyed by water saturation, something we are told won't happen with closed cell foam.

Both balsa and foam cores work well as long as proper practices are followed. People seem to think because it has closed cells, foam gives a license to take short cuts. I posted the link to the article to show that foam can be vulnerable to water penetration just as balsa can.

Foam is lighter than balsa, balsa has siginficantly better engineering properties. You can build a very good boat with either.

Both of these material, balsa and foam, may have better INDIVIDUAL properties unto themselves, BUT when combined in a boatbuilding sandwich core there are other consideration that may downgrade their positive attributes.

[beiland]

"There are hundreds of Duflex boats around the world. AFAIK none have had problems with wet cores. But why not contact ATL and ask them? ATL Composites - engineering resin foam waterproofing carbon fibreglass adhesive fairing boat repairs structural fibreglass."

Originally Posted by johny1973

I know of a number of Duflex boats which have suffered rotten/soggy balsa cores as a result of water entering via a deck fitting etc, and spreading, even transiting z joins on a schionning in QLD.

And one Oram that a large void in the core was located prior to painting, just two laminates of glass with a veneer under each and no balsa at all.

ATL would be the last place who are going to volunteer information on core failures (for what ever reason) on there product.

I thought this posting was worth repeating as I went back thru this subject thread post-by-post

[beiland]

Originally Posted by Esprit Marine

Alan, yes you're right, no quality system is totally foolproof. But at least this means that ATL have a stringent quality control in place, and that they have an obligation to address registered complaints and improved quality.

The quality obtained with the DuFlex panels will anyway be superior to what most builders are able to achieve in their yard with traditional construction methods. Working with strict environmental (hygrometry, temperature...) conditions, and oven post-curing of epoxy built boats, are beyond the means of the average cruising yacht builder, and are generally reserved to highly priced racing boats.



There is one famous example of "apaling quality" advertised by an amateur boat builder, as cited by 44'cc. I don't deny that he had some issues with the DuFlex panels he received, but as stated before he has chosen to make it a personal war. Before ordering the first CE kit, I visited ATL, discussed the above with them, and I can tell you they were well aware of the complaint, have followed it seriously, and they have convinced me that they are doing what is necessary to ensure continuous improvement of quality.

Personally I am satisfied with the DuFlex panels we've received, and I believe that most of the professional builders are -I have not heard of any builder having stopped using DuFlex, and no DuFlex boat having to be hauled out and repaired, because of quality issues on the product. This, added to the fact that prestigious architect offices such as Nigel Irens have trusted the product enough to use it on B&Q and Sodebo racing catamarans, should speak in itself and counterbalance the few quality issues raised here and there by one or two amateur builders.

P.S. : before you say so; no, I am not a reseller of DuFlex panels or kits.

Thanks, that was a good recommendation for their products.

[beiland]

Originally Posted by 44'cruisingcat

Which bodes well for the longevity of Duflex boats, if properly built. With generally heavier laminates and cores with better structural properties.

A friend is building using foam cores (vertical strip) but he is using considerably heavier laminates, not because they are needed to handle structural loads, but to resist the knocks and dents of day to day use.

Many keep referring to these 'structural properties of the cores'.

Exactly what particular properties of these cores are the most important?....all of them, or just several?

Or is it really how the combination of the core and the skins work together?....not the individual properties necessarily. I'll expand on this later.

[colemj]

Originally Posted by beiland

Many keep referring to these 'structural properties of the cores'.

Exactly what particular properties of these cores are the most important?....all of them, or just several?

Or is it really how the combination of the core and the skins work together?....not the individual properties necessarily. I'll expand on this later.

Depends. Compression strength is important in some areas and shear in others. Same with stiffness (although that is more of a combination property). Insulation properties could be important for some boats, etc.

Mark

[44'cruisingcat]

Originally Posted by beiland

I thought this posting was worth repeating as I went back thru this subject thread post-by-post

I note you didn't bother to post subsequent discussion, where Johnny's "observations" were shown to be more like imaginings.

The way DuFlex is made, there is no possibility of there being large voids between the laminates. Where there is no balsa, solid resin will fill the void.

As I've said, more than once - don't just rely on what you READ. Get some samples, and check them out for yourself. If you're happy with what you find, then great.

[44'cruisingcat]

Originally Posted by beiland

Many keep referring to these 'structural properties of the cores'.

Exactly what particular properties of these cores are the most important?....all of them, or just several?

Or is it really how the combination of the core and the skins work together?....not the individual properties necessarily. I'll expand on this later.

The core is supposed to hold the laminates in a constant position relative to each other. When you bend a panel, the laminates will want to move closer together, and to slide or sheer relatively to each other.

So compression and sheer properties of the core are what will make a panel stiff. Lack of compression strength in the core can be compensated for by adding thickness. Panel stiffness can also be increased by increasing laminate weight. Both of these measures increase the overall weight.

[beiland]

Originally Posted by olliric

....So, you seem to indicate that balsa is the worst of core materials. Yet it is the one with greater mechanical properties. Here is the spec of duflex panels with the same skins and core thickness.
Balsa: 5.1 Kg/Sqm, 3.4 mm deflection, 35 Kpa pressure to failure
Foam: 3.6 Kg/Sqm, 4.2 mm deflection, 30 Kpa pressure to failure

Where did you get these figures?

With identical skins and core thicknesses I am surprised you would find that great of a difference in bending deflection. To me it indicates that the skin layups are too light such as to make the cores themselves need to resist the bending. The cores should not be subjected to this responsibilty in a proper construction.

Here are some opinions on the issue.
Structural Issues : Core Materials

Good one, I'll have to read thru that.

[beiland]

Originally Posted by 44'cruisingcat

I note you didn't bother to post subsequent discussion, where Johnny's "observations" were shown to be more like imaginings.
No I did not see that....yet??

The way DuFlex is made, there is no possibility of there being large voids between the laminates. Where there is no balsa, solid resin will fill the void.
I can believe that....I think. But didn't I see some other references to this same void problem somewhere?

As I've said, more than once - don't just rely on what you READ. Get some samples, and check them out for yourself. If you're happy with what you find, then great.

The problem with that little 'individual testing' one could never uncover all of the variables that one could find posted on the internet. And I am not relying on just one forum to gather as much info as possible.

[44'cruisingcat]

The core on Duflex is easily visible too. I mean it's as easy to see as print on a page. It's hard to believe anyone could get to the "prior to painting" stage without noticing any voids.

Anyway, I've seen hundreds of sheets of Duflex, and no voids.

[aclmck]

Originally Posted by beiland

The problem with that little 'individual testing' one could never uncover all of the variables that one could find posted on the internet. And I am not relying on just one forum to gather as much info as possible.

You need to build something out of the sheets then you will understand how they perform, how they can be bent, how they can be used, the internet is full of armchair critics.

When you have used the product you will then understand what this system can acheive and why a "VOID" would be detectable, this is why great products fail, Idiots take shortcuts, they don't core correctly (soggy decks) and they assume they know best.

New generation products MUST be used as designed to achieve the required result, deviations result in Failure.,(Complete failure Mostly)

[beiland]

So I guess all of you naysayers are telling me my armchair research is useless. I'm sorry, I just may be advancing a train of though that is beyond your comprehension. I think Maltese Falcon met similar response initially.

So here are a few other 'far-out thoughts'.




BIG BANG #1, Lion Whelp's impact test

These two brothers bought an older 65' Alden schooner, and went about restoring and upgrading her. They had a MAJOR concern with hull integrity,

“When you're doing 9 or 10 knots at night there's no way you can see a log or container just under water ahead of you. It's a probability issue," Phin says.
He points out that right after a hurricane in 2003 a whole load of telephone poles came off a container ship in the vicinity of Bermuda. The poles were 120 feet long and 3 feet thick, plenty big enough to sink a yacht. There was also a sea buoy loose in the area and that buoy was 10 feet in diameter”.

So they built some test panels to do a little investigating. One panel was built to the same layup as the original hull, and another two panels were backed up with 3” thick NidaCore PP. Laying around their boatyard they had some old pieces of railroad track (pretty tough stuff). They picked out a 6 foot long, 157 lb section, and proceeded to drop it onto the test panels, not flat sided, but end on,.....first from 9 feet, then 16',..... and finally 30 Feet......WHAM !!


.....excerpted from an article that appeared in Soundings mag,
Building a Bullet Proof Boat
http://www.soundingsonline.com/boat-shop/on-powerboats/266332-building-a-bulletproof-boat

.....Have a look at some of the photos and the damage here:
Testing the NidaCore
http://www.portlandyacht.com/lionswhelp/whelp.html


Brian's Note: Not a very 'professional test', but impressive in its own right. Sure speaks to the ductile nature of the PP honeycomb core material. This ductility is a good match for the ductile nature of steel itself.
**********************************************

…...from that same article,

The problem with a conventional plank-on-frame hull is that you have the planking on the outside of the ribs and the ceiling on the inside, with a void that's the thickness of the ribs between them," Phin says. "If you puncture the hull planking, you can't get to the damage to stop the leak because the ceiling is in the way."
They bonded 3-inch-thick Nida-Core - the same thickness as the ribs - to the planking with WEST System epoxy. "Then we glassed over the Nida-Core from the inside with epoxy 10-08* glass creating a smooth surface on the entire inside of the hull, from sheer to sheer," Phin says. "Next, we epoxied a 5/8-inch fir tongue-and-groove ceiling over everything and painted that. We created a monocoque [one piece] structure, a continuous I-beam that added a great deal of strength and impact resistance to the hull, as well as thermal and acoustical insulation.

...hmmm, I wonder if we could eliminate some of the numerous smaller ribs and stringers of the conventional welded-up steel hull and substitute some PP core material bonded to the steel skin??....might save a lot of welding time, and hull plate distortion. IDEA??

[beiland]

Here is a descriptive word I do not often hear of when the subject of sandwich cores comes up....'ductile'.

I think this 3M site (new owner of NidaCore) probably has one of the more precise discussions.

Originally Posted by excerpt

Core materials have one or more intrinsic properties that are advantageous for specific applications, and these properties must be carefully considered when designing composite structures. Just as composite laminates have specific properties determined by the selected reinforcements and matrix resins, sandwich panels take on many additional characteristics that are uniquely determined by the selected core material. Distinguishing materials by their respective limitations, including strain-to-failure, is as important for core as it is for fibers and resins. Elasticity has been an essential issue in the debate concerning the risks of introducing brittle fibers like carbon, or opting for the damage tolerance provided by aramid fibers, such as Kevlar. When it comes to core material, it is also helpful to compare characteristics in relation to elasticity and damage tolerance. Of the commonly used core materials, balsa and aluminum honeycomb are among the least elastic. Polymeric foams demonstrate a wide range of properties, depending on their specific formulations and densities. In general, thermoset polymers are less elastic than thermoplastics. Urethane-based foams are thermoset, and are the least elastic of the polymeric foams. PVC foams demonstrate a wide range of elasticity, from blended "cross-linked" foams to "linear" foams. Of the foam types commonly used, SAN (Styrene-AcryloNitrile) Foams are the most forgiving, but cost is at a premium. It also is common in foams for the temperature resistance to decrease when their elasticity is increased.

This is RIGID-ELASTIC TECHNOLOGY. This is 3M. By comparison, 3M thermoplastic honeycombs (or RIGID-ELASTIC TECHNOLOGY) have elasticity in the 200 percent range! In real-life terms, the better the elasticity, the greater the IMPACT STRENGTH and derived TOUGHNESS.

Or, in reverse comparison, the stiffer the core material, the better it transfers impact and vibration energy from the side of the impact (or outside skin) to the inside skin, thus subjecting the inside skin to face buckling, delamination or catastrophic failure.
The basic design criterion for RIGID-ELASTIC TECHNOLOGY is damage tolerance - a measure of the panel's retention of its structural properties after damage compared with its undamaged properties. It is considered desirable for core to deform elastically yet remain intact with the facings. This enables a panel to support a considerable percentage of its designed dynamic loads, despite the damage. In theory, this property can be advantageous when parts are designed to be "under-built," that is, they have the damage tolerance calculated into the part itself, thus saving weight and cost.

Nida-Core Lightweight Honeycomb Panels - Specific Rigidity, Energy Absorption, Visco Elasticity, Composite Sandwich Panel

[aclmck]

Originally Posted by beiland

So I guess all of you naysayers are telling me my armchair research is useless. I'm sorry, I just may be advancing a train of though that is beyond your comprehension. I think Maltese Falcon met similar response initially.

So here are a few other 'far-out thoughts'.




BIG BANG #1, Lion Whelp's impact test

These two brothers bought an older 65' Alden schooner, and went about restoring and upgrading her. They had a MAJOR concern with hull integrity,

So they built some test panels to do a little investigating. One panel was built to the same layup as the original hull, and another two panels were backed up with 3” thick NidaCore PP. Laying around their boatyard they had some old pieces of railroad track (pretty tough stuff). They picked out a 6 foot long, 157 lb section, and proceeded to drop it onto the test panels, not flat sided, but end on,.....first from 9 feet, then 16',..... and finally 30 Feet......WHAM !!


.....excerpted from an article that appeared in Soundings mag,
Building a Bullet Proof Boat
http://www.soundingsonline.com/boat-shop/on-powerboats/266332-building-a-bulletproof-boat

.....Have a look at some of the photos and the damage here:
Testing the NidaCore
http://www.portlandyacht.com/lionswhelp/whelp.html


Brian's Note: Not a very 'professional test', but impressive in its own right. Sure speaks to the ductile nature of the PP honeycomb core material. This ductility is a good match for the ductile nature of steel itself.
**********************************************

…...from that same article,


...hmmm, I wonder if we could eliminate some of the numerous smaller ribs and stringers of the conventional welded-up steel hull and substitute some PP core material bonded to the steel skin??....might save a lot of welding time, and hull plate distortion. IDEA??

Yep got all that, so now you want to use this material as a glued on stringer to a Steel Skin???

Have you contacted any of the designers to ask about this, how the differential movements will effect the attachment points etc. Composite panels have been used with various metal skins in the building and construction industries now for some time with varied success, i would think it possible, ask one of the composite panel companies if they have an approved system.

You completely miss the point though about the composite panels, the designers of these panels were once considered radical and were told they would never work,thousands of boats floating around the world are proving this to be different, and yes their are many instances where sadly "CORNERS HAVE BEEN CUT" and failures occur. not unlike any other product out there(Osmosis in Glass for one dis-similar metals another)

The facts are these panels lend themselves to be excellent building products when used correctly, and as the designers intended, they save weight over common products and are extremely easy and cost effective when providing a custom one off boat .They were possibly designed for the catamaran market hence the large sheets.

Unfortunately they often require a fair amount of knowledge not just during the building but after when having fittings attached to ensure a watertight core.

i have built boats using a couple of different composite systems so understand these points, i often see fixtures fitted that in a couple of years will give problems with wet cores etc not unlike those in an aluminium boat using stainless steel fittings that are not properly isolated.

When building with new generation products most of the new designs also allow for watertight bulkheads and voids which in turn allow a holed boat to float and in some cases continue to a port to be repaired especially in a catamaran ( we have seen on this forum a cat with no hull bottoms floated to a port after being removed from a reef)

i know problems exist when these products are used away from the designers system, but then so do most other products.

[nimblemotors]

Originally Posted by aclmck

You need to build something out of the sheets then you will understand how they perform, how they can be bent, how they can be used, the internet is full of armchair critics.

When you have used the product you will then understand what this system can acheive and why a "VOID" would be detectable, this is why great products fail, Idiots take shortcuts, they don't core correctly (soggy decks) and they assume they know best.

New generation products MUST be used as designed to achieve the required result, deviations result in Failure.,(Complete failure Mostly)

Count me in the armchair camp, but it is a definite disadvantage if a material must be used in tightly controlled ways, and otherwise would fail.
Having re-cored a balsa cored boat that was soggy (speedboat),
I tend to think it has downsides.
It just might be fine until 10-20 years later, when the boat isn't pristine and all 'as designed' anymore. No boat remains that way.
It seems to be boats made to be light in particular, can't take much of a beating, and get holed and sink rather too 'easily' in my view.

I am personally leaning to building my hulls using solid glass,
but still researching options.