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Old 02-04-2013, 17:36   #1
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Duflex (Balsa cored panel construction) Questions.

Hi,

I'm looking into building a big catamaran 40-50 feet, and I'm curious what the ups and downs of Duflex construction might be, and what the Pro's and Con's are of owning one once the boat is completed.

I'm wondering how they hold up after sustaining damage, and with the cored construction... if water intrusion from damage travels outside of its "panel."

A "normal" balsa cored boat built in a mold, can have water track from one end to the other, eventually... I'm wondering if the damage remains in just the panel size, and stops at the scarfs or Z joints.

Thanks,

Zach
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Old 02-04-2013, 17:42   #2
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On this balsa cored boat the water has always stopped at the edge of the individual block. A block is maybe 3cm square. This is a very well built 1982 boat. Cored everywhere.

I would think there are better materials available now. Honeycomb or some uncrushable foam. They are still subject to problematic water intrusion with damage. But not the same mess.
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Old 03-04-2013, 01:42   #3
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Re: Duflex (Balsa cored panel construction) Questions.

Balsa used for boat building is end grain balsa. That means that the panel is made out of several small blocks of balsa which cut cross wood grain and jointed with epoxy. Theoretically water intrusion will stop within each block. Duflex are panels of end grain balsa core covered usually in one or two layers of 600 gr glass each side. If you carefully fill out all holes and throughhulls with epoxy or solid glass it should be ok. There are many production boats which are made out completely or partially of Balsa (Lagoon, Leopard).
The problem of Duflex panels is that you have to make hard chine hull (no curves are possible) or made first canoe body using mold - depending on your plans and design. Personally I am not a big fan of Duflex because here in EU prices are absolutely noncompetitive. Its better use balsa as core for infusion or vacuum bagging method. But in Australia it is a very popular material for DIY catamarans.
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Old 03-04-2013, 15:44   #4
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Re: Duflex (Balsa cored panel construction) Questions.

Duflex is also available with foam core, if balsa coring is too much of a concern. Check with your designer, as some changes might be required in laminate and core thickness, to compensate for foam's inferior structural properties.

Also, compound curves ARE possible, by cutting the Duflex into strips and strip planking. But hard chine construction is certainly faster.

There would be almost no chance of water crossing from one panel to another, through a Z join.

Our boat is Duflex, we're very happy with the material. The construction method is fast, the material is very light and strong. It's not cheap though.

Some photo's of the build process here: Member Galleries - Cruisers & Sailing Photo Gallery
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Old 03-04-2013, 16:43   #5
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Re: Duflex (Balsa cored panel construction) Questions.

Spirited designs Spirited Designs - Home of the Spirited 380 by Craig Schionning amongst others, get over the issue of the hard chines at the bottom by suppliying a pre-made canoe style fibreglass hull bottom. It cuts many hours off the kit build, it isn't duflex and can be easily strengthened.
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Old 04-04-2013, 23:33   #6
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Re: Duflex (Balsa cored panel construction) Questions.

Thanks for the replies.

44Cruisingcat... it was actually your boat that inspired the question. Nice work and a finely fitted yacht indeed. Are your cleats fiberglass?

Thanks for the link to the Spirited designs, that is an interesting method to get a sleek boat out of flat panels.

Has anyone seen a duflex boat that has been through an episode of pounding in the surf, or hit a reef? I'm curious about the stiffness, vs overall strength.

Thanks,

Zach
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Old 04-04-2013, 23:46   #7
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Re: Duflex (Balsa cored panel construction) Questions.

There's a thread on here about the Spirited that hit "something" and sank shortly after. Also google that one and you should easily find it, off South Australia. There was much debate over what it hit and how many other types wouldn't have sunk in the same situation etc etc.
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Old 05-04-2013, 00:30   #8
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Re: Duflex (Balsa cored panel construction) Questions.

Quote:
Originally Posted by Zach View Post

Has anyone seen a duflex boat that has been through an episode of pounding in the surf, or hit a reef? I'm curious about the stiffness, vs overall strength.

Thanks,

Zach
Dunno about pounding through the surf, but friends who own a 16 metre schionning G force have had it 45 knots 6-7 metre seas for a couple of days in the coral sea, and it handled it beautifully. A well built duflex boat will be strong and reliable.
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Old 05-04-2013, 01:10   #9
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Re: Duflex (Balsa cored panel construction) Questions.

Think there was an Oram that ran up on a reef with very little damage.
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Old 05-04-2013, 04:45   #10
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Re: Duflex (Balsa cored panel construction) Questions.

As an owner and part builder of a duflex built boat,i can assure you they are super strong and stiff.
We have motered into short 8ft seas with green water over the bows with hulls slaming into the troughs, the boat handles it well ,my wife and dog not so well.
Besides steel it is probably the stiiffest boat i have ever set foot on.
We were even hit in the bow by a 2000T container ship in Borneo while we were of the boat and it did little more than " briuse" the paint work. No structural damage what so ever.
As long as it is built well and deck gear is installed correctly ,its a great material
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Old 05-04-2013, 15:33   #11
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Re: Duflex (Balsa cored panel construction) Questions.

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Originally Posted by ausaviator View Post
There's a thread on here about the Spirited that hit "something" and sank shortly after. Also google that one and you should easily find it, off South Australia. There was much debate over what it hit and how many other types wouldn't have sunk in the same situation etc etc.
Incorrect. The Spirited that hit "something" didn't sink. The leeward hull was the one damaged, it flooded and the boat capsized. Didn't sink. It was washed up on a beach somewhere in the Great Australian Bight, and I believe may have been recovered.

I don't think a Spirited 380 would sink, under any circumstances.
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Old 05-04-2013, 15:41   #12
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Re: Duflex (Balsa cored panel construction) Questions.

Quote:
Originally Posted by Zach View Post
Thanks for the replies.

44Cruisingcat... it was actually your boat that inspired the question. Nice work and a finely fitted yacht indeed. Are your cleats fiberglass?

Thanks for the link to the Spirited designs, that is an interesting method to get a sleek boat out of flat panels.

Has anyone seen a duflex boat that has been through an episode of pounding in the surf, or hit a reef? I'm curious about the stiffness, vs overall strength.

Thanks,

Zach
Yes, the cleats and staunchions are fibreglass.

"Outahia" the first Oram 44C launched, was sailed onto rocks on Great Keppel. Apart from rudder damage incurred when reversing off the rocks, she was undamaged.

Another Duflex boat was capsized in heavy weather in a Bris-Gladstone race, was washed up inverted onto a beach, pounded by surf for a few days, dragged into an upright position by tractor - allowed to fall onto it's hulls from the vertical position - and is now crusing again. Needed the cabin rebuilding, but from the decks down was virtually intact. The boat floated so high the diesels had barely gotten wet. They're still in use.

It's a tough material. Kilo for kilo, there wouldn't be much around to match it.
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Old 05-04-2013, 15:46   #13
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Re: Duflex (Balsa cored panel construction) Questions.

I intended to research further and got sidetracked, my apologies. It sunk a hull from memory as most other cats would with a gaping hole in the side. Guess it depends on what your definition of sunk is :-) Ultimately frp is frp and as long as the panels are glued together correctly you're not likely to sink any time soon. A very tidy unit you have there 44ftcat.
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Old 05-04-2013, 16:15   #14
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Re: Duflex (Balsa cored panel construction) Questions.

44C beat me to it. Sink is

Quote:
sink 1 |siNGk|
verb ( past sank |saNGk| or sunk |səNGk|; past participle sunk |səNGk| )

• (of a ship) go to the bottom of the sea or some other body of water because of damage or a collision: the trawler sank with the loss of all six crew members.
So no didnt sink. Like I said earlier - built right and used right Duflex is fine.
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Old 07-01-2014, 19:49   #15
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Re: Duflex (Balsa cored panel construction) Questions.

Can anybody recommend a good source of Duflex panels in the U.S.?
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