Are Cats Made from Duflex Panel Kits Strong ?

[olliric]

I very much like most of the Australian cats offered in kits and I am considering building the Spirited 480.
However, being a marine engineer I am used to steel construction I am a bit puzzled about the structural strength of composite construction using kit technology.
I have seen many pictures of the method of assembly and although I do agree that the panel construction is potentially strong I have reservations on the areas in the hulls where loading is concentrated.
In particular anchoring of the cross beam, chain plates, engine beds, rudder stock bearing, cleats, winches, car tracks and most other fittings.
I wonder about the life expectancy of such boats given that are often fast boat that lend themselves to be sailed really hard, I would do with mine .
I would hate building one only to have few years down the road delaminations, water penetration cracks and so forth.
I also wonder about the performance and cons of composite chain plates.

Given that one day I may want to sell such cat, what is involved in having the boat certified in compliance to EU safety standard category.

I searched the net and I have not found independent insights on these issues. I hope some can shed some light

Cheers

[Robertcateran]

Done well they are well strong enough. Biggest potential problem is not sealing any holes made and allowing water into the core. I have no idea how they rate in the EU safety standard, but they put up with some pretty nasty seas off Australia and NZ. The inertial forces are much less in the lightweight construction, ad the designs are well sorted in terms of reinforcing where needed and distributing stress.

[Nordic cat]

Some of the Scionning boats have CE documentation, just ask them. I would go for a foam kit rather than Balsa, the resale value of Balsa boats is often much lower.
The boatyards say this keeps them in business in some places

For a bit more than the price of a kit boat, you can probably get a finished boat built to your requirements. There is a company in Peru building Kelsall cats at very resonable prices.

Hope this helps

Alan

[Esprit Marine]

Olliric,

The following differences can be highlighted between a catamaran built from a DuFlex kit, and one built with a traditional male or female tooling method :

- the DuFlex panels are laminated under hot press. Although the same pressure benefits (high lamination strength, low resin content) can be achieved in situ with vacuum infusion construction, the heat curing allows to double the strength of the fiber-epoxy. This is equivalent to boats built in pre-preg and oven cured, a process generally reserved to racing boats.
- The 'Z-joint' assembly between the DuFlex panels, has a strength which is from tests up to 20% less than that of the board. This is taken into account by ATL composites for the scantlings calculations.
- The Duflex kits for the CE Spirited catamarans, are totally different than for the Australian Spirited. The Duflex panels thicknesses and laminates have been calculated for each panel with regards to exposure to wave and CE category, in accordance with CEN ISO 12215-5.
- The main advantages of Epoxy as compared to Ester resins, is low porosity and high resistance to fatigue. Whereas a polyester or vinylester boat will have lost around 35% of its strength after only one year in the water, an epoxy built one will have lost only 10%.
- Anchoring of cleats, winches, tracks and other fittings is done with marine plywood reinforcements and additional lamination, as any traditional boat building.
- All structural elements are Epoxy bonded together, whereas a large production boat will have separate Vinylester sandwich hull / Polyester sandwich deck / 'RTM Eco' monolithic roof / plywood bulkheads, sometimes with silicone sealant to join all together...

I hope this sheds light on your queries.

[44'cruisingcat]

Originally Posted by Nordic cat

Some of the Scionning boats have CE documentation, just ask them. I would go for a foam kit rather than Balsa, the resale value of Balsa boats is often much lower.
The boatyards say this keeps them in business in some places

For a bit more than the price of a kit boat, you can probably get a finished boat built to your requirements. There is a company in Peru building Kelsall cats at very resonable prices.

Hope this helps

Alan

The balsa cored kits also cost much less than the foam cored. Resale values of Duflex boats in Australia is excelent. Duracore too. (Both balsa cored materials) AFAIK no Duflex boat has had to visit a boatyard due to problems with it's core. But in less enlightened countries paying the considerable premium for foam might be worthwhile.

The duflex kit for an Oram 44C is around $65,000 - $70,000 Aus. How cheaply could you have a similar sized Kelsall built in Peru?

[44'cruisingcat]

Originally Posted by olliric

I very much like most of the Australian cats offered in kits and I am considering building the Spirited 480.
However, being a marine engineer I am used to steel construction I am a bit puzzled about the structural strength of composite construction using kit technology.
I have seen many pictures of the method of assembly and although I do agree that the panel construction is potentially strong I have reservations on the areas in the hulls where loading is concentrated.
In particular anchoring of the cross beam, chain plates, engine beds, rudder stock bearing, cleats, winches, car tracks and most other fittings.
I wonder about the life expectancy of such boats given that are often fast boat that lend themselves to be sailed really hard, I would do with mine .
I would hate building one only to have few years down the road delaminations, water penetration cracks and so forth.
I also wonder about the performance and cons of composite chain plates.

Given that one day I may want to sell such cat, what is involved in having the boat certified in compliance to EU safety standard category.

I searched the net and I have not found independent insights on these issues. I hope some can shed some light

Cheers

Unless you intend to build something extremely big, or very slow, steel isn't a viable material for multihulls. Composite materials have been widely used for decades. Cats can be built from aluminium though, if you really don't like the idea of composites. (You might also want to avoid flying if that is the case.)

Composite chainplates are built in such a way as to spread their loads over a very wide area. I'd say they are superior to stainless ones in this regard, where the load is really only transferred to the area sandwiched between the chainplate and it's backing plate. Composite ones don't tend to leak either.

Duflex hasn't really been around long enough to be able to say with certainty "it will last a hundred years" but I know people who have sailed over 30,000 nm with a Duflex boat. No problems with cracking, delamination etc.

[Nordic cat]

Originally Posted by 44'cruisingcat

The balsa cored kits also cost much less than the foam cored. Resale values of Duflex boats in Australia is excelent. Duracore too. (Both balsa cored materials) AFAIK no Duflex boat has had to visit a boatyard due to problems with it's core. But in less enlightened countries paying the considerable premium for foam might be worthwhile.

The duflex kit for an Oram 44C is around $65,000 - $70,000 Aus. How cheaply could you have a similar sized Kelsall built in Peru?

44C: Have a look here for the pricing.

They quote a finished 46 foot hull at 55k US$ for materials (Divinycell) and 80 k $ for the complete hull build.

A finished "ready to sail" 46 ft cat at 350 k $ which sounds very reasonable.

Link: Kelsall Catamarans - Ballotta Catamarans - Custom built catamarans - Prices


Alan

[olliric]

Originally Posted by Esprit Marine

Olliric,

The following differences can be highlighted between a catamaran built from a DuFlex kit, and one built with a traditional male or female tooling method :

- the DuFlex panels are laminated under hot press. Although the same pressure benefits (high lamination strength, low resin content) can be achieved in situ with vacuum infusion construction, the heat curing allows to double the strength of the fiber-epoxy. This is equivalent to boats built in pre-preg and oven cured, a process generally reserved to racing boats.
- The 'Z-joint' assembly between the DuFlex panels, has a strength which is from tests up to 20% less than that of the board. This is taken into account by ATL composites for the scantlings calculations.
- The Duflex kits for the CE Spirited catamarans, are totally different than for the Australian Spirited. The Duflex panels thicknesses and laminates have been calculated for each panel with regards to exposure to wave and CE category, in accordance with CEN ISO 12215-5.
- The main advantages of Epoxy as compared to Ester resins, is low porosity and high resistance to fatigue. Whereas a polyester or vinylester boat will have lost around 35% of its strength after only one year in the water, an epoxy built one will have lost only 10%.
- Anchoring of cleats, winches, tracks and other fittings is done with marine plywood reinforcements and additional lamination, as any traditional boat building.
- All structural elements are Epoxy bonded together, whereas a large production boat will have separate Vinylester sandwich hull / Polyester sandwich deck / 'RTM Eco' monolithic roof / plywood bulkheads, sometimes with silicone sealant to join all together...

I hope this sheds light on your queries.

Thank you guys for the replys.

I'll play the devil's advocate. A discussion on this subject is good as I don't think I am the only one that is a bit puzzled and fascinated by these kick ass aussie cats.
Being 30% lighter these Australian cats are far superior in most areas and particularly in performance than any other built with conventional methods. Are the people that build other performance cruising cats such as Outremer, Dolphin, Fastcats and Fredys stuck in the stone age? Are their buyers out of their mind paying a lot more for a lot less performance?

Going back to technical stuff:

I agreed that the strength of Duflex panels including the Z joint is excellent. However it seems that most Duflex component panels are joint together on the boat without the Z joint. The glue is squirted in the irregular gaps between the panels and covered with glass strips. The glue in the joint is most likely discontinuos with different thickness and most probably there are air gaps. In the angled joint the coving helps but does not eliminate the discontinuity in material and geometry which create a stress raiser. The mechanical property of such joint is probably a fraction of that of the parent material adjacent to it.

The other concern is the Duflex's resistance to compression in areas of high load. I articulate my doubts a bit better.
I have seen pictures of sail drive flanges clamping on a plain opening in the Duflex or other areas where a simple 10 mm plywood reinforcement and some fiberglass layer compresses the Duflex in between with steel fasteners. After a while I would expect the clamping force and load on the fitting to create a permanent set in the panel and create a path for moisture attack. In such areas solid glass or core of harder woods would be more appropriate.
Filling the holes with epoxy helps stop the water penetration but does not increase the strenght of the panel much.

I agree, you can't beat epoxy. Does that compensate for the above?

Are the EC Spirited scantlings higher and more conservative than the Aussie's? Can the EC certification be obtained for the Aussie version.
In Europe and probably other places selfbuilt boats and one offs have low resale value compared with production or established yard boats. The lack of CE certification would compound the problem and make them very hard to sell.

I must say that on paper these Australian Duflex cats and in particular the Spirited 480 are overall the best and I am totally seduced.
I just hope that it's not too good to be true

Cheers

[44'cruisingcat]

Originally Posted by Nordic cat

44C: Have a look here for the pricing.

They quote a finished 46 foot hull at 55k US$ for materials (Divinycell) and 80 k $ for the complete hull build.

A finished "ready to sail" 46 ft cat at 350 k $ which sounds very reasonable.

Link: Kelsall Catamarans - Ballotta Catamarans - Custom built catamarans - Prices


Alan

$350k US is roughly $500k Aus. That's probably little or no cheaper than you could have a Duflex kit boat built here in Aus. Friends had an Oram 44C built by Streamline Catamarans Streamline Catamarans: Sailing Catamarans for less than that.

A Schionning would cost more, being a more expensive kit, and more complex to build though.

[44'cruisingcat]

Originally Posted by olliric

Thank you guys for the replys.

I'll play the devil's advocate. A discussion on this subject is good as I don't think I am the only one that is a bit puzzled and fascinated by these kick ass aussie cats.
Being 30% lighter these Australian cats are far superior in most areas and particularly in performance than any other built with conventional methods. Are the people that build other performance cruising cats such as Outremer, Dolphin, Fastcats and Fredys stuck in the stone age? Are their buyers out of their mind paying a lot more for a lot less performance?

Going back to technical stuff:

I agreed that the strength of Duflex panels including the Z joint is excellent. However it seems that most Duflex component panels are joint together on the boat without the Z joint. The glue is squirted in the irregular gaps between the panels and covered with glass strips. The glue in the joint is most likely discontinuos with different thickness and most probably there are air gaps. In the angled joint the coving helps but does not eliminate the discontinuity in material and geometry which create a stress raiser. The mechanical property of such joint is probably a fraction of that of the parent material adjacent to it.

The other concern is the Duflex's resistance to compression in areas of high load. I articulate my doubts a bit better.
I have seen pictures of sail drive flanges clamping on a plain opening in the Duflex or other areas where a simple 10 mm plywood reinforcement and some fiberglass layer compresses the Duflex in between with steel fasteners. After a while I would expect the clamping force and load on the fitting to create a permanent set in the panel and create a path for moisture attack. In such areas solid glass or core of harder woods would be more appropriate.
Filling the holes with epoxy helps stop the water penetration but does not increase the strenght of the panel much.

In areas of high compression the core should be removed and replaced with a higher density core, usually marine plywood. Having said that, balsa is very strong in compression, and people I know neglected to replace the balsa core in the area under their mast base, even though the plans did state they should have.

After more than 20,000nm there was just beginning to be evidence of some movement there. The repair was simply a matter of doing what the plans had called for in the first place, but with the added complication of having to unstep the mast.

I can only refer to my own boat, ( http://www.cruisersforum.com/gallery...00&userid=3477) but in it any highly stressed panel or bulkhead joins are made using two staggered 750gsm triaxial tapes. The main mast and rear beams have large unidirectional flanges top and bottom, giving them the structure (and appearance) of large I beams.

The glue in the panel joins does basically the same job the core does - it holds the laminates apart. The presence of some air bubbles in the glue is pretty much irrelevant, as long as the glassing is done properly - the core, whether balsa or foam, is largely comprised of bubbles anyway.

[Glenn C]

another question I had with the flat panel boats is the stiffness of the flat panels, compared to a curved panel. Something to do with 'the moment of inertia' of the section I believe. Presumably the flat panels could flex more around bulkheads causing a hard spot over time and greater fatigue. Anyway is this relevant, or is insignificant when considering the likely deflection within the expected loading?

[44'cruisingcat]

The "flat" panels are almost always bent into a curve.

[Glenn C]

ok thanks. I had assumed that it would be difficult to bend these panels post cure, but then I was thinking only short lengths, whereas, thinking about it, the panels could be made quite long and easier to bend. But then only a small curve would be required I guess to significantly improve the stiffness.

[catty]

Originally Posted by olliric

Thank you guys for the replys.

I'll play the devil's advocate. A discussion on this subject is good as I don't think I am the only one that is a bit puzzled and fascinated by these kick ass aussie cats.
Being 30% lighter these Australian cats are far superior in most areas and particularly in performance than any other built with conventional methods. Are the people that build other performance cruising cats such as Outremer, Dolphin, Fastcats and Fredys stuck in the stone age? Are their buyers out of their mind paying a lot more for a lot less performance?

Going back to technical stuff:

I agreed that the strength of Duflex panels including the Z joint is excellent. However it seems that most Duflex component panels are joint together on the boat without the Z joint. The glue is squirted in the irregular gaps between the panels and covered with glass strips. The glue in the joint is most likely discontinuos with different thickness and most probably there are air gaps. In the angled joint the coving helps but does not eliminate the discontinuity in material and geometry which create a stress raiser. The mechanical property of such joint is probably a fraction of that of the parent material adjacent to it.

The other concern is the Duflex's resistance to compression in areas of high load. I articulate my doubts a bit better.
I have seen pictures of sail drive flanges clamping on a plain opening in the Duflex or other areas where a simple 10 mm plywood reinforcement and some fiberglass layer compresses the Duflex in between with steel fasteners. After a while I would expect the clamping force and load on the fitting to create a permanent set in the panel and create a path for moisture attack. In such areas solid glass or core of harder woods would be more appropriate.
Filling the holes with epoxy helps stop the water penetration but does not increase the strenght of the panel much.

I agree, you can't beat epoxy. Does that compensate for the above?

Are the EC Spirited scantlings higher and more conservative than the Aussie's? Can the EC certification be obtained for the Aussie version.
In Europe and probably other places selfbuilt boats and one offs have low resale value compared with production or established yard boats. The lack of CE certification would compound the problem and make them very hard to sell.

I must say that on paper these Australian Duflex cats and in particular the Spirited 480 are overall the best and I am totally seduced.
I just hope that it's not too good to be true

Cheers

I'm not sure that the spirited boats have any balsa below the water line.
This link may provide interesting reading. Are balsa panels water resistant?.
Building a Catamaran.. Outgassing?

[44'cruisingcat]

The 3 spirited 380's I have seen all have balsa as the core in the moulded parts both above and below the waterline.

As for the experiment conducted by TCP's editor, that has Duflex boat builders simply scratching their head. It's well known and accepted that the weave on a Duflex panel should be filled before painting. It's a simple matter of applying a runny epoxy glue mix with a squeegie or trowel. Why someone would go to that much trouble to "prove" what is already well known it is a mystery.