Are Cats Made from Duflex Panel Kits Strong ?

[olliric]

Originally Posted by catty

What actual experience has bob got? Is bob a qualified naval architect? Is bob a qualified engineer?. Is bob a qualified shipwright?. Which other designers out there think a large balsa cruising cat with a flat bottom is a good idea? Do designers in Europe and north America think balsa below the waterline is a good idea? Or is bob just a lovely guy who likes to draw boats to the best of his ability.

Well, I think that there are quite a few of the Duflex boat designers that do not have higher education or titles. Yet their boats are popular which should indicate that they do work.
Unfortunately being relatively new, I suspect that it is still unclear for how long these cat can last. That is my main concern. I wish there were more hard evidence to know the whole story. This lack of information is probably one of the reasons that makes thise boats hard to sell in most markets.
As regard having balsa below the waterline, although it is not a common choice, I believe there are builders that use that solution. The weight saving is considerable and explain in part the superior performances of duplex cat compared to molded ones.
One of the problems with balsa below the water line is the difficulty in assessing the condition of the core. Unless the damage is extensive it is difficult to find troubled area. That alone can make the purchase of a used boat quite a gamble.
Boats, Yachts: High Tech Materials in Boat Building

[Esprit Marine]

Originally Posted by Esprit Marine

Indeed the Spirited 480 is available CE certified. Difference in kit weight has not been worked out by Craig Schionning yet, but with extrapolation from the 380 it should be around 400 kg.

I am happy to report that, although the skin thicknesses have been substantially increased, this has been counterbalanced by the use of superlite balsa (100 kg/m3) for deck and roof sides, and Craig has now confirmed that the weight impact will be 150 kg only.

[Nordic cat]

Originally Posted by Esprit Marine

I am happy to report that, although the skin thicknesses have been substantially increased, this has been counterbalanced by the use of superlite balsa (100 kg/m3) for deck and roof sides, and Craig has now confirmed that the weight impact will be 150 kg only.

What would it have been otherwise? Does this figure also take into account the increased epoxy uptake in the more porous balsa?

regards

Alan

[Esprit Marine]

Alan, the DuFlex panels are manufactured under hot press by ATL Composites. The fibre content is approximately 62% by weight with E-glass in the finished panel.

ATL strictly control the manufacture process under a Germanischer Lloyd approved quality control, and the weight figures they give are accurate.

By the way, how is the construction of your cat going ?

[Nordic cat]

Originally Posted by Esprit Marine

.

The 62% by weight is for the glass/epoxy weight ratio not for the whole panel.

Using ATLs own numbers for the standard 150 kg/m3 balsa, a simple calculation shows that there is 1100 grams/m2 epoxy in the first layer of the glass/wood bond, whereas the second layer of glass only needs 900g/m2.

As ATL has not published numbers for the super light balsa panels, my gut instinct is that they will absorb even more epoxy, and thereby not generate as big a weight saving as expected, but this is just an idea, not something I know for sure.

Quality control systems, even approved ones are no guarantee for accurate specifications, unless there have been registered customer complaints, (that the company itself registers), and the company has taken correct corrective action.

As you probably know, there have been some examples of apalling quality from ATL as published here and elsewhere.

It's on hold until the market picks up again....


cheers

Alan

[cat man do]

Originally Posted by johny1973

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.

.

Really?

So what stopped the light glass skin flopping around in the breeze if there was no core?

Veneer you say? well that would sound more like Durakore to me, not duflex durakore - Google Search and I would have thought was before Bob Oram started

And, there were some boatbuilding suppliers around years back selling a cheaper knockoff to Durakore that did have voids, one sample I saw even used what appeared to be resorcinol to glue the veneer to the balsa.

Dave

[44'cruisingcat]

Dave, that post you were responding to was pure B.S. I asked Bob about this and he had never heard of it. He keeps in pretty close contact with owners of his boats, and if it had happened he would have known about it, and he would have ensured ATL did something about it.

As for the so called "appalling quality control", well that's pretty much B.S. too. The kit referred to in TCP was as bad as it gets, and frankly, if he had followed the advice of experienced Duflex builders, (and the warning about removing peelply before use which is on EVERY SINGLE SHEET of Duflex) he would have had no problems whatsoever.

What's more ATL contacted Bob Oram, and they both looked at the kit, and evaluated what was required to rectify it, (even though the issues were largely due to the instructions being ignored) and ATL gave The builder materials to effect those repairs (which were pretty minimal) and money to pay for hired labour to do it.

Bear in mind this is a guy who blames the designer for his own failure to properly read the plans:

I found an anomaly in the plans that will cost a little work but it could have been worse. The big red arrow and the dotted line it points to are objects I put there to show the actual end of the chamfer panel. The dotted line to the left of that is where the plans indicated the end of the chamfer panel. The problem it caused was that I was about to cut off material on the deck panel as it appeared to be over long relative to the chamfer panel. I stopped short of making the cut but did do the under deck support before I found out the error in plans. see below.. I was just about to cut off the deck panel to be even with the chamfer panel as the plans indicated. As it is I will have to scarf in another piece of pipe for the support and fair it off later. It turns out that the deck is meant to overhang the chamfer panel. I have made the designer aware of the problem so assume it will be fixed in future plans but this makes a good point about keeping alert. I give myself a C+ grade for spotting it before I cut but after the support glassing.


NOWHERE Does it say to cut the deck panel!

Under a big red "NOTE" it clearly states: "Trim INNER SHEER PANEL and CHAMFER to final length when fitting BWBB."

To clarify, BWBB = Back web, back beam. The back web is fitted AFTER the two hulls are joined. This builder hasn't even got to this stage yet. So not only was he cutting the wrong part, he was doing it at the wrong time. But somehow, to him, that's the designer's fault.

I could go on, I know this guy fairly well, but won't bother for now.

[Esprit Marine]

Originally Posted by Nordic cat

Quality control systems, even approved ones are no guarantee for accurate specifications, unless there have been registered customer complaints, (that the company itself registers), and the company has taken correct corrective action.

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.

Originally Posted by Nordic cat

As you probably know, there have been some examples of apalling quality from ATL as published here and elsewhere.

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.

[bayview]

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.

As a point of interest whats the difference in cost between a balsa cored pannel (2400 x 1200) and a foam cored pannel?

[Esprit Marine]

Originally Posted by bayview

As a point of interest whats the difference in cost between a balsa cored pannel (2400 x 1200) and a foam cored pannel?

Im my opinion not an easy answer. You could obtain from ATL the difference of price for panels with the same core thickness. But as foam has far less strength and modulus than balsa, foam core will need to be thicker. So a full scantlings calculation needs to be run on the yacht structure to determine the exact price incidence, and I am not sure the weight saving, if any, will justify the substantial cost impact on cruising yachts.

If your concern is water penetration in the balsa core in case the skin gets punctured, then this link might help you understand that no core material is perfect. Anyway, not even considering weight issues, I still prefer a GRP epoxy hull with foam or balsa core, to a Polyester or Vinylester monolithic hull; see there.

[catty]

Originally Posted by Esprit Marine

Im my opinion not an easy answer. You could obtain from ATL the difference of price for panels with the same core thickness. But as foam has far less strength and modulus than balsa, foam core will need to be thicker. So a full scantlings calculation needs to be run on the yacht structure to determine the exact price incidence, and I am not sure the weight saving, if any, will justify the substantial cost impact on cruising yachts.

If your concern is water penetration in the balsa core in case the skin gets punctured, then this link might help you understand that no core material is perfect. Anyway, not even considering weight issues, I still prefer a GRP epoxy hull with foam or balsa core, to a Polyester or Vinylester monolithic hull; see there.

Mmmmmm, A Tennant 11m meter bridge-deck cat we built over 10 years ago for a cruising sailor, had a pretty standard hull layup of 12mm foam core with 600g outside and 400g inside. Its still in abfab condition I hear. It would be interesting to see how one could possibly build that lighter in balsa.

Maybe someone could work out what minuscule % this would add to the finished cost. The resale value would certainly be better than a balsa cored boat. Why bother with balsa I ask?.

[44'cruisingcat]

Originally Posted by catty

Mmmmmm, A Tennant 11m meter bridge-deck cat we built over 10 years ago for a cruising sailor, had a pretty standard hull layup of 12mm foam core with 600g outside and 400g inside. Its still in abfab condition I hear.

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.

Schionnings do offer some of their Duflex kits with the option of foam cores in the Duflex. The kit cost is significantly greater, and the weight saving is fairly small.

[cat man do]

Originally Posted by Esprit Marine

But as foam has far less strength and modulus than balsa, foam core will need to be thicker.

Neither core has any across panel strength and relies on the glass to provide that, which is where I like strip plank, I reckon you get the equivalent of a few hundred GSM of unis fore and aft in the plank and in the opposite direction some as well, definitely more than foam or Balsa.

Good to hear another example of a light build catty, makes my 600gsm in and out on a 16mm Kiri core sound almost reasonable.

Pumpkin Eater is another light one, I think she was a Crowther shockwave 37 with 400 in and out on a 10mm foam core, I may be mistaken anyone remember?

Dave

[cat man do]

Originally Posted by 44'cruisingcat

Dave, that post you were responding to was pure B.S.

Thought as much

Dave

[johny1973]

I am glad you have all talked yourselves into it. Quote: from Wallace Gouk AMS®
Port Credit Marine Surveys:


BALSA CORE = COMPOST
This article is concerned with balsa cored bottoms. Wet and even rotten balsa cored decks are an ugly and expensive but much less serious issue dealt with in other articles on this site.

You may think this title a little harsh but given the amount of rotten balsa I see through my surveys I think it is warranted. Many fine boats have been built with balsa core and many 30 year old balsa cored hulls are still sound today but many are not and it sometimes takes a very experienced eye to tell the difference.

This article was prompted by the experience of a friend in Toronto who bought a 2002 model boat, titled and launched in the spring of 2004 and after spending only 16 weeks in water developed a crack at one of two throughulls over the winter storage period.

He asked for my advice and I told him to pull the throughull fittings as it was not unusual for the builders to forget to seal the core after drilling a hole for the fittings......guess what......he removed the fittings and found saturated balsa core at one of the throughulls. He asked me to take a look and I found about three square feet of very wet core around that throughull. I found this by percussive sounding and using my moisture meter. It is very likely that the crack was caused by the water expanding as it froze over the winter.

Moisture levels were taken with an Electrophysics, capacitance type digital meter calibrated to a dry test panel and set at the 0.5 scale. Relative meter readings are interpreted as follows 10-12= low, 13-16= slightly elevated, 17 - 20 = elevated, 21 + = high

Now if you have read my other article on "Moisture Meter Myths" then you know that I do not fully trust these meters however, as this boat has never had any antifouling paint to confuse the meter, the bottom was clean gelcoat and the vessel had been out of the water all winter, I feel quite comfortable with the readings I found. Most of the hull checked sound with moisture levels reading 11-13 while the areas around the head intake throughull checked dull and read 29-30. I do not find this acceptable in a modern vessel after only 16 weeks in water and five months dry storage. It should also be noted that high moisture levels were also found around the I/O transom assembly cutout, another area of exposed wood the builders frequently forget to seal. Unfortunately I have found that many boat surveyors know little about moisture meters so the best defense is to read my article "Moisture Meter Myths" so you will know if your marine surveyor knows what he is talking about.

To see this high moisture level in the core in a modern vessel which has spent only 16 weeks in water is in my opinion inexcusable and certainly does not suggest a long healthy life for this boat. The exposed core at both throughulls and the crack at one of them will certainly shorten the life of the core in my friends boat not to mention the transom !

The Manufacturers Point of View

The manufacturers of balsa and balsa cored hulls tell us that wet balsa in a hull does not compromise its structural integrity. They claim that moisture spreads very slowly if at all horizontally due to the end grain cut of the balsa core. They are also state that balsa will not rot (even with high moisture content) unless it is exposed to oxygen and go on to claim that if properly installed, no oxygen will get to it, therefore it cannot rot. They state that water permeating through FRP does so at a molecular level therefore with so little oxygen it cannot support fungal growth. They also say that frozen, saturated core cannot fracture FRP or cause the core to separate from the FRP.

One manufacturer states " There are standards for balsa core when used in production. There are no standards in regard to core once it is encapsulated in a laminate".

The Flip side

Their arguments are heavily qualified by "if " . If the core is properly fitted and properly sealed (inside and out) and if there are no penetrations by fasteners, throughulls or fittings. they may be right. Unfortunately few boats are built the way core makers would like.

First….. If water is getting into the core so is oxygen, that's why it's called H2O. It gets there not by permeation at a molecular level but through improperly fitted throughulls, screws through the inner FRP in the bilges and often right through resin starved, poorly applied chopped FRP on the hull interior.

Second..…. Even though the water will contain oxygen, wood will rot without it due to the presence of anaerobic bacteria. Much like a compost heap, the real decay occurs deep in the pile where aerobic (oxygen requiring bacteria) cannot survive but where an anaerobic bacterium thrives. Do a google on "anaerobic, balsa, decay" just for fun.

Third….. Water will travel much more slowly horizontally through the balsa if the ends are near perfectly encapsulated and all the kerfs in the balsa are filled with resin. I have never seen a core sample in which all the kerfs were filled and the core /laminate joint was void free. I doubt you will find any surveyor who has.

Fourth..…. While saturated core may not pose an immediate threat to the vessel it will definitely lead in that direction as the extra 800lbs. cannot do it much good. As a basic rule of physics we all know that water is not compressible and when the water filled xylem (capillaries in the balsa) are slammed into a 2-3' wave at 20knots the entrapped water will burst through the xylem walls thus hastening a horizontal movement of the water and weakening the core. David Pascoe (Yacht Survey Online: David Pascoe, Marine Surveyor) has termed this process "hydraulic erosion", an apt description I think. Don't forget that the xylem walls may have already been weakened by the anaerobic bacteria feeding on the lignin which is the glue that holds the xylem together.

Fifth.....They claim that a saturated, frozen area of core will expand into unsaturated area and not up (or down) to the FRP skin. Take a look at the photo at right which shows the side rail of a stainless steel tube ladder that had about one foot of water in the lower part of its 6' length. If they were right, the water should have expaned up the tube instead of bursting through the side.

You will never keep water out of a balsa core but I have seen many30 year old sailboats with balsa cored hulls which still show only very slightly elevated moisture content (and some that were rotten).

Lets take a look at my own boat..........................
(These are not "bottom" examples but are the best shots I have) The four photos below show the inside surface of the bulwarks around my decks where I cut out the inner skin to expose the "compost". Keep in mind that these bulwarks are about 18" above the water line and the cored transom section is 3' above the waterline and that there are no holes of any kind for fasteners, through hulls or anything else. ......................... So why did I have to dig out about 30lbs. of COMPOST ?

YES ! that is exactly what it looks like and it is a miserable job. So if this can happen 18" above the waterline. Imagine what can happen to balsa below the water line if everything is not installed to PERFECTION ! Then ask yourself when you have seen anything done on a production boat to perfection.

The two photos above are 3' above the waterline and the two below are about 18" above the waterline. These photos show the FRP skin as it was just cut off and a close up of .....you guessed it....COMPOST.
Now if this can happen 3' above the water line, how on earth can the manufacturers claim in good conscience that it does not happen below.

What does this mean to a surveyor....
On decks, wet or rotted core is usually easy to detect because the FRP skin is generally thinner than the hull and therefore more easily sounded and moisture meters are more reliable because they are not confused by multiple layers of who knows what kind of bottom paint. Wet or rotted core can be more difficult to detect on bottoms or stringers as the FRP skin may be too thick for the meter to read through and metallic compounds in multiple layers of different bottom paints may also confuse the meter. If the core has rotted and is not in contact with the skin again the meter may not pick up the moisture.
If the vessel being surveyed is blocked or on a trailer, the pressure of the support points may mask an area of core separation or rot. Percussive soundings may be less reliable for the same reasons. A surveyor must be cautious about moisture statements and core condition because sometimes the only way to be sure is to cut a hole and look !

What does this mean to the boat owner.....
A saturated core will eventually separate from the FRP skin and I still believe this can be hastened by our freeze thaw cycle here in the Great White North. If our winters can fracture cast iron water pipes and heave our roadways, what do you think it does to the microscopically thin cellulose of the balsa. The skin can crack and allow in yet more water. At 10lbs. per imperial gallon of water, how much of this stuff do you want to carry around in your core. Pounding a 7000lb boat at 18 knots through a 2-3' chop will certainly put a strain on your saturated core. How easy will it be to sell a wet core boat with cracks all over the bottom ? Quick, put on another couple of coats of bottom paint, maybe the buyer won't notice !

So, can a quality boat be built with a balsa bottom ? Yes they can and are but it requires great care and attention to details like relieving all balsa in areas with deck fittings, throughulls or even just screws.
Boats are built with balsa because it can be cheaper (maybe not if you do it right) and lighter than achieving the same initial strength with solid FRP. Are you willing to bet that your builder wants to build cheap but then pays the extra attention required to do it right.

Wallace Gouk AMS®
Port Credit Marine Surveys

Happy sailing... however long it lasts