Are Cats Made from Duflex Panel Kits Strong ?

[Nordic cat]

Originally Posted by 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.

This experiment shows the major shortcoming of Balsa IMO, as it allows water to spread across the grain, even though many claim that this is unlikely.

Foam is more foregiving...

Alan

[catty]

Originally Posted by 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.

.

So the paint keeps the balsa dry?

[olliric]

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

Yes, It's an interesting price. However the design is not my favourite. I need a boat as fast as possible. I am not retired and I work 4 weeks on/ 4 weeks off. Every time I only have about 25 days of vacation for cruising. I don't want to spend too much time on passages when I relocate the boat to a different area.

[44'cruisingcat]

Originally Posted by Nordic cat

This experiment shows the major shortcoming of Balsa IMO, as it allows water to spread across the grain, even though many claim that this is unlikely.

Foam is more foregiving...

Alan

Foam would get wet too. The point is, the laminate has the minimum amount of resin required. Possibly the sheets he had had even less than that - the quality of his kit wasn't as good as any other I've seen.

[44'cruisingcat]

Originally Posted by catty

.

So the paint keeps the balsa dry?

Generally the laminate is sealed when you buy it, but it has a grain that needs filling. In the event it was porous, the epoxy you squeegie on seals the laminate. Fairing compound, highbuild primer and paint all add more protection. What do you think keeps the steel dry on a steel boat, or the timber dry on a wooden one?

[olliric]

Originally Posted by 44'cruisingcat

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.

Of course steel is a no go for performance. However aluminum is. Too bad that there aren't many who build cat with it. I have just sailed a 16m high performance aluminum mono (Alubat Cigale 16) and I was blown away by the stiffness, solidity, comfort and performance. It's my ideal cruising mono.

The concern I have on composite chain plates has to do with cyclic stress.
My fear is that over time there is a risk of delamination. I also wonder why the vast majority of yards and designers still use stainless steel on fiberglass. Why didn't they figure it out in the decades they been using composite for everything else.
The composite chainplates greater resistance to leaks is quite a good advantage that should have pushed the whole industry to adopt it. Leaks in way of fittings is possibly one of the most common problems with composite.

Yes, it's probably early to speculate on life expectancy of Duflex boats

[Nordic cat]

Stainless steel chainplates are relatively cheap, fast and easy to mount in practically the same way for the last 50 years. People know and understand this, so no reason to make the sell of the standard boat any more difficult....

The same goes for stainless steel rigging, todays fibres are much lighter and easier to make up, yet very few use these today.

I've changed to synthetic rigging last year, and am happy with it


Composite chainplates need some extra care and attention to detail during the build, and some of the high end racers have been using this for a number of years. For a one-off build it is the way to go IMO..

Alan

[44'cruisingcat]

AS Nordic says, SS chainplates are cheap, and little skill is needed to fit them. They can also be turned out in large numbers cheaply. Composite chainplates take a little more care and a few more hours to make them.

Production boat builders don't neccessarily use the best practise in building their boats. Far from it. Would a production builder be able to charge more for a boat with composite chainplates as opposed to SS ones? Unlikely, but the composite ones would cost more to make, and so reduce his profit margins.

[44'cruisingcat]

Originally Posted by Nordic cat

Foam is more foregiving...

Alan

At least that is what the foam manufacturers tell us. Boats, Yachts: High Tech Materials in Boat Building

[Esprit Marine]

Originally Posted by olliric

Are the EC Spirited scantlings higher and more conservative than the Aussie's? Can the EC certification be obtained for the Aussie version.

Yes, the EC Spirited scantlings are higher and more conservative than the standard Aussie 380. The CE Duflex kit weights 300 kg more than the Australian kit (mainly in biax skins), and part of it is compensated using Superlite Balsa core. And no, the EC certification cannot be obtained for the Aussie version.

Olliric, where would you sail and what would be your typical programme (cruising distance etc) during those four weeks breaks ?

[David_Old_Jersey]

Originally Posted by olliric

Of course steel is a no go for performance. However aluminum is. Too bad that there aren't many who build cat with it.

I have previously wondered about Aluminium not being widespread on cats. Is it a size thing? - i.e only works (weight vs strength) on the larger builds?

[44'cruisingcat]

I looked into aluminium a little. One thing I found is that it's much harder to finish the interior of an aluminium boat. A Duflex or glass boat can be painted inside, which keeps it light. With alloy you have to build frames to support a liner, which all needs to be removable to access the hull. It all adds weight, as well as being extra work.

[Robertcateran]

Aluminium is a weight versus size thing. Part of it is finding enough stiffness for the skin without going to heavy or having ribs and stringers everywhere. Dinghies get around this to some extent by having ribs pressed into the skin. Aluminium is still significantly heavier at the 40' mark but Easton in Australia seems to be doing quite a nice job of making them pretty quickly and reasonably light. There is also the problem of fatigue and electrolysis. Notwithstanding there are quite a few aluminium multihulls sailing around the world.
I was going to build a 40' Crowther motor-sailing catamaran aluminium fishing boat before the bottom fell out of fishing. In composites I would save about a third the weight .
There are other ways to go rather than foam and balsa. Polypropylene honeycomb is starting to get some traction, and there is also strip plank.
Have a look at Pacific Cats website for a comparison in using polyprop honeycomb core. If you really want to go light, have a look at the Harryproa website where concentrating all sailing loads into a relatively small area significantly reduces weight.

Much of a multihulls weight is in the beams and reinforcing to provide support for the sailing loads. The scantlings are only one part of the equation. Making heavier scantlings then introduces greater inertial forces and sailing loads.

[olliric]

Originally Posted by 44'cruisingcat

AS Nordic says, SS chainplates are cheap, and little skill is needed to fit them. They can also be turned out in large numbers cheaply. Composite chainplates take a little more care and a few more hours to make them.

Production boat builders don't neccessarily use the best practise in building their boats. Far from it. Would a production builder be able to charge more for a boat with composite chainplates as opposed to SS ones? Unlikely, but the composite ones would cost more to make, and so reduce his profit margins.

I see the point. I would not mind spend more time for a composite chain plate as long as it is less prone to problems

[olliric]

Originally Posted by 44'cruisingcat

At least that is what the foam manufacturers tell us. Boats, Yachts: High Tech Materials in Boat Building

Interesting site and articles. However, I believe that if one wants performance has to compromise somewhat. If I were interested in building a boat that can take the battering of dock pilings during a hurricane I would chose metal, no solid fiberglass like the surveyor recommends.
All I want is a boat that is fast but can take the beating of a storm or years of fast offshore sailing without problems. I am not interested in having a collision proof vessel. Multis are already pretty safe in that regard.