Shocked by hull material catamaran

[arsenelupiga]

Originally Posted by Cruising4Christ

Nope. I deal with this at our law firm. In this case, NOT disclosing this type of structural damage would be considered fraud, and the only party with monetary damages resulting from these photos are the 'would be' buyers. The owner may not be stoked, but he has no recourse...not to mention international statute nightmares.

ok, you the expert. just my thinking...

If someone took pics of repair of my hull and badmouth on internet, would not be happy for sure:

"Shocked by hull material catamaran"

[daletournier]

Originally Posted by Cruising4Christ

Random question and I know there would be drawbacks, but has anyone ever built, purchased, or seen any type of 'skid plates' for use in heavy coral or rocky areas where running aground is more of a consideration than performance?

Maybe just a removable nose cone with a deeper draft to absorb a lot of energy like a car bumper? It could be a 'V' shape that connects to the bow, lightweight, stowable, sacraficial and relies on geometry for strength. ???

My first boat was a Wharram tiki 31 (modified sloop rig). It had stainless steel shoes along each hull. Wharrams have a stich and glue v hull(s) set up, so was easy to run a approx 1 inch stainless strip.

Sent from my vivo Y35 using Cruisers Sailing Forum mobile app

[valhalla360]

Originally Posted by Cruising4Christ

Random question and I know there would be drawbacks, but has anyone ever built, purchased, or seen any type of 'skid plates' for use in heavy coral or rocky areas where running aground is more of a consideration than performance?

Maybe just a removable nose cone with a deeper draft to absorb a lot of energy like a car bumper? It could be a 'V' shape that connects to the bow, lightweight, stowable, sacraficial and relies on geometry for strength. ???

They have those for jetskis and bass boats. The problem is they don't provide much (if any) structural benefit. They are almost purely for abrasion.

For a large cruising boat, anything that would help structurally would be a major add-on. Easier just to get an old overbuilt full keel boat with 2" solid fiberglass hull...but even that is no guarantee if you hit something hard enough.

[Just Another Sa]

Originally Posted by tp12

I'd guess that well over 90% of all Schionnings are balsa and definitely not due to price considerations.

Jeff talks about materials (options, considerations) here,for anyone who is interested: Material Choices | Jeff explains composites

Some comments about the content of that link:

Foam is stronger than honeycomb type cores, both the paper and the plastic.

Only if comparing foam to honeycomb with less density, like Jeff did.
There are aluminium honeycombs too, some of them much stronger than any foam typically found in boats.

Balsa is also far better than foam or honeycomb in sheer. This is when the core sample is held flat between your hands, one hand slid one way and the other slid the opposite way, when the core tears through the middle the core has failed in sheer.

For the same thickness it is, but for the same core weight the difference is not that relevant, foam is good enough when using a suitably thick one.
Thicker foam also allows for less skin laminates, unless point loading dictates otherwise.

The amount of stretch you feel before the core shears is shear stiffness.

No it is not. That is shear strain to failure, not stiffness and they are not dependent on each other by any mathematical function.
Stiffness of material is the relation between stress and strain.
Stiffness of an object will also depend on size, not just material used.

So 13mm Balsa may be equal in sheer to 19mm Foam.
...
Generally a balsa or WRC shell is noticeably stiffer than a foam boat using equivalent laminates.

No, exactly the opposite. With equivalent laminates the thicker foam core is much stiffer.

Thirdly, foam absorbs a lot more resin into the open surface cells than timber and so increases weight.

That depends on type of foam and timber. Some foams consume far less than others and also less than balsa. Balsa absorbs low viscosity resins much more than ones with higher viscosity. But balsa can always be sealed on the surface with quickly curing type resin just before use, if hand laminating. With resin infusion ...

The end result using Foam in my experience is always a heavier shell with less stiffness. Professional builders can achieve a good result but usually use vacuum bagging and very good molds to achieve this.

The Wilderness 1230 has a foam option. It weighs 200kg less than the Balsa version.

So according to Jeff a foam boat is heavier but weighs less?!?
I can't even comment on that one.
Neither is foam less stiff, if it's thicker and also has thicker laminates as he stated they would be according to his plans to spread the compression loads.

Both foam and balsa are suitable materials for boat construction, when used correctly. I don't find that text as neutral presentation for their pros & cons.

[44'cruisingcat]

Originally Posted by daletournier

Wow....Geoff Schoining told you that? , or?' please elaborate?

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There's also the fact that after a fairly acrimonious split, Craig Schionning (Spirited cat's) still uses balsa cores in his boats. You'd think, if foam were so much better, he'd have used foam cores as a point of difference and selling point. You know, to make his dad "look silly".

But he doesn't.

[BigBeakie]

If balsa cores produced an intrinically stiffer structure, then the French racing multis would be balsa. They are not balsa, they are foam.

These boats are highly engineered using the best materials available, regardless of cost. Balsa is OK to save money and for some very high HDT applications depending on resin used, but it is so vulnerable to rot, why bother?



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[44'cruisingcat]

Racing boats aren't intended to last as long, or to carry the payloads, or to have people walking around on them wearing shoes, or to cop minor bumps without denting. Racing boats have thin laminates, light cores and are fragile.


But even then, it's not unheard of for balsa to be used in high load areas like beams and bulkheads.

[catsketcher]

Ok I am not a trained engineer but there is a lot here that does not make sense.

Honeycombs - I have used Nomex and plastic honeycomb. I have never seen aluminium used apart from once in Fossets Playstation cat. So we can rule out aluminium as a valid choice.

Shear stiffness - The amount of stretch in a material per unit of force is the strain - that is the amount of movement you feel. Stiff materials exhibit less strain than stretchy materials for the same force. I think Jeff was trying to get neophytes to understand the basics here and was using reasonable layman terms.

Equivalent laminates - it is reasonable to suggest that balsa gives stiffer laminates. Schionning was a builder before he became a designer. His boats have flat panels and he really needs to understand stiffness. I would go with someone who has built tens and designed hundreds of boats that use balsa. Foam boats with light laminates can become soft. It is a problem with lots of
light laminate foam boats - monos and multis - they can get softer as the years go on. Balsa boats don't seem to get soggy. Go feel a well used Laser deck - it will delaminate or core fail after a few years no exceptions.

We also have the French multi question. I wrote before how John Levell, the engineer for Nigel Irens, used balsa core in Ellen Macarthur's B and Q tri because of its excellent mechanical properties. The best designer and the best engineer used balsa because it made sense in the underwater areas - they didn't use high density foam. Boatspeed haven't made any more Formula One multis since Sodebo in 2007 so I haven't seen any since then but the best tris in the world used balsa, where applicable, ten years ago.

I have two good friends who made Schionning balsa core boats and they spent hundreds of thousands of dollars building. If foam was a better option they would have gone foam. They had plenty of money and Schionning knew it. After using Duflex you get hooked. Bob Oram told me it hurt to buy it but it was a great material to use. ATL will make kits from foam if you want. Schionning will get you a foam kit if you want. I can't believe that the owner of the best boatyard in Australia - Tony Longhurst from Boatworks, who is a very rich man, would get a multi million dollar balsa cat built in balsa core if it was a bad material. It is obvious that it is not.

My mate who built his 13.2 metre schionning did some tests on antifoul as he built his boat. It took 5 years. He got some cutouts and put different types of copper epoxy on the Duflex cut outs he had and weighed them down outside his waterfront home. He didn't edge them and left them for over a year in the water. The edges got a bit mucky but about 1cm in the balsa was fine - after a year with no protection. He was very happy with the balsa core because he was open minded and did the experiment. No problem with edge grain balsa.

What I don't get is how people who aren't engineers, boat builders or designers can "get shocked" by hull laminates. I think the people who do lots of building and designing know a lot more than a weekend sailor who has never built a boat, we should respect the experts experience and knowledge. Our boats have only come so far because we have learnt from each other and absorbed the lessons of history.

cheers

Phil

[arsenelupiga]

hahahaha, guys normally badmouthing lagoon, suddenly defend lagoon building method

because they use the same method.

Of course lagoon has no clue after 3000 cats built and they were just lucky this time.

[Seaslug Caravan]

[QUOTE=Just Another Sa;2324566]


So according to Jeff a foam boat is heavier but weighs less?!?

[UNQUOTE]


Yes , his logic does crack me up.

For those interested here is a really good thread that explains the engineering differences between foam and balsa.

Pay attention to posts by GROPER.



GROPER does a superb job explaining , and takes "one" step by step through the engineering calculations, for those interested.

/diy-yachts.com/forum/viewtopic.php?f=18&t=993

[Night_Sailor]

Originally Posted by tuskie

Yep. I agree. Interesting that smaller Lagoon models of that era (380, 400, 420, 421, 450) utilise hull construction with solid glass below waterline. Newer model Lagoons (L42) are balsa cored below WL, as are newer Fountaine Pajot, as are all Leopard models. Most "performance catamarans" are fully cored composite. If the fibreglass is epoxy, it will be even thinner.

My research shows that the newer Fountain Pajot hulls are solid glass below the waterline.

In addition to hydraulic damage to core materials, repetitive slamming will turn balsa into dust. While that is more of a problem for powerboats, it is something to consider for offshore sailing. It's less of a problem, above the waterline where the stresses are vertical.

[tuskie]

Originally Posted by Night_Sailor

My research shows that the newer Fountain Pajot hulls are solid glass below the waterline.

Please elaborate. What is your source? My source is my eyes.

Being familiar with the Lavezzi, Belise and Bahia models, which are solid glass below waterline and foam above. I was surprised when I observed balsa core in the bilges of a new Helia. It was unmistakable; squares of balsa visible through a clear laminate inner skin. Also visible in floor of engine room. Not sure about the new Lucia, haven't been on one.

[arsenelupiga]

above waterline if front bow in L 400 one can see balsa is in 0.5 m x 0.5 m blocks separated by around 0.5 - 1 cm of fiberglass. I assume they are water isolated from each other to minimze damage of water intrusion to 1 square. One would think they are additionally wrapped in some sort of hard to penetrate plastic for further protection

Will such approach be used under waterline, or insulation introduces structurally weak points ?

[Moody Mike]

My old Moody54 was balsa cored . Very strong boat but had much thicker lay up than what I see on this cat. I had some wet balsa around a poorly fitted transducer. It only penetrated about 3 inches into the balsa. Easily removed & solid glasses.

[barnakiel]

Nothing wrapped in plastic btw as the balsa cubes must be glued well to both skins. Otherwise there is no sandwich laminate benefit.

Wrapping the core in plastic would induce delamination at the very start. A NO and NO.

If they build something like this or that it is nearly always saving on labour in case of mass produced boats. Keep the costs low, get a higher margin. BAU.

b.