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Carbon PVC sandwich - Skin thickness?


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No single answer, the point of composite laminates is to engineer the laminate schedule according to load paths.

That said, for a general rule, the minimum skin thickness in [non-reinforced areas] is probably going to be limited by the # of layers required to orient the loads & resist puncturing, rather than the absolute minimum calculated required strength.  So most likely [at least] 1-2 layers of biax and a layer of uni, or maybe 3 layers of uni oriented at 0/30/30 at about .012-.015" per layer, vaccuum bagged & cured. A rough approximation is to add 60-100% thickness & weight to the raw carbon material, for a complete laminate.

But really if you're going to the expense of carbon, it should be engineered and layed up using vacuum-infusion to maximize the material characteristics.

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1 hour ago, Reference said:

No single answer, the point of composite laminates is to engineer the laminate schedule according to load paths.

That said, for a general rule, the minimum skin thickness in [non-reinforced areas] is probably going to be limited by the # of layers required to orient the loads & resist puncturing, rather than the absolute minimum calculated required strength.  So most likely [at least] 1-2 layers of biax and a layer of uni, or maybe 3 layers of uni oriented at 0/30/30 at about .012-.015" per layer, vaccuum bagged & cured. A rough approximation is to add 60-100% thickness & weight to the raw carbon material, for a complete laminate.

But really if you're going to the expense of carbon, it should be engineered and layed up using vacuum-infusion to maximize the material characteristics.

yes, agreed, it should be engineered, eventually, but when doing preliminaries on costs, best methods etc. scantlings or other rules of thumb are useful. Could not find scantlings on carbon sandwich, maybe I didn't look hard enough. 

>0/30/30 at about .012-.015" per layer, vaccuum bagged & cured

Thanks. This helps.  

So around 1mm?

from the 0/30/30 assuming the zero is most critical (depending on bulkhead spacing)  

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2 minutes ago, fastyacht said:

Setimrs y ou need to do some prelim eng desgn to beable to makr a useful wgt est.

Blowing smoke rarelyvworks. Unlesscyoi are Hunter S Thompson

I'd like some of what you're smoking 

If you don't know the answer it's ok to admit it

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Stating the obvious, but overall size of the boat matters too. Something like a J/22, the minimum carbon thickness for strength is going to be determined by what's available in cloth, whereas a 50' boat, that 2/3 layers would likely be of insufficient strength to carry the loads.

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18 minutes ago, Reference said:

Stating the obvious, but overall size of the boat matters too. Something like a J/22, the minimum carbon thickness for strength is going to be determined by what's available in cloth, whereas a 50' boat, that 2/3 layers would likely be of insufficient strength to carry the loads.

Seems logical.

There are most certainly some rules of thumb or scantling calcs, on these as there are with fiberglass or wood etc. 

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Seriously why are you asking?  If you are considering building a boat ask the designer. If you are doing a proper cost estimate you should have some preliminary plans as a bare minimum. 

Way too many variables to even guess. Vacuum bagged? Resin infused? Pre-preg?

If you are doing a cost estimate the difference in cost of guess A and guess B won't matter. Why?

An 80' catamaran has many, many thousands of manhours of labour in it. It will dominate the cost estimate rather than material costs of the skin.

Ask SOMA about Gunboat construction costs...

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10 minutes ago, nota said:

is there a conversion factor for the same hull in glass vs carbon lay up

a X weight of glass per sq = Y weight of carbon per sq ?

No. Because if the question is "what is the minimum required", that answer may reflect the available cloth rather than the absolute strength.

I know someone who just reskinned a fiberglass sport boat in carbon. It's not going to weigh any less than before, b/c 2 layers of carbon laminate weighs about the same as 2 layers of fiberglass even if it's stronger.  And just because carbon is stronger/stiffer, you can't get away with half a layer of it.

 

 

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Umm, just a chippie but I heard somewhere that safety factors vary upon intended use. A cruising boat may use a 3x load factor, a racing yacht 2x or less, fortunately (?) insurance adjusters seem generally unaware of this. You are actually getting some expert replies here, some estimate these projects on weight. A designer should have a target weight he can provide, different builders will have different costs per kg. Then factor in how do you feel about holes in the hull.

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1 hour ago, Ryan.. said:

I'd like some of what you're smoking 

If you don't know the answer it's ok to admit it

Hey I docthis forca living. I have MDD. Do as I recommenx amd tou too will be hi on life and your boatcwill float on its limes

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57 minutes ago, Reference said:

No. Because if the question is "what is the minimum required", that answer may reflect the available cloth rather than the absolute strength.

I know someone who just reskinned a fiberglass sport boat in carbon. It's not going to weigh any less than before, b/c 2 layers of carbon laminate weighs about the same as 2 layers of fiberglass even if it's stronger.  And just because carbon is stronger/stiffer, you can't get away with half a layer of it.

 

 

News flash. Carbon isvnotv stronger. Only stiffer. On square area. Somewhat stronger ontex basis. It is stiffer.

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3 hours ago, Zonker said:

Way too many variables to even guess. Vacuum bagged? Resin infused? Pre-preg?

Assume 60/65% fiber volume fraction. 

We are able to guess just fine with fiberglass scantlings .. all I need is 3 variables to get skin thickness for those.. why would carbon be any different ?

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You understand that a 80' boat weighs about double a 60' boat if it is a geosim right? So maybe the skin thickness to handle what is getting to be global loads might differ.

1mm is a good starting point as a bare minimum for a 60' version. There. Now go and price out a multi million dollar boat on that basis.

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45 minutes ago, Ryan.. said:

May want to let the AC builders know that secret, would save them huge 

It's fine, they already know. Of course they do :

2 hours ago, Reference said:

invest the time/$$ in design & quality construction techniques,

So they get the benefit :). (They also seem to like using aluminum honeycomb for core, and only an insane person would consider that for a boat that actually had to spend any time in the water :) )

There are plenty of aircraft makers who make very light efficient structures with glass sandwich construction. Especially once you get the skins down to 1 or 2 layers.

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13 minutes ago, JohnMB said:

There are plenty of aircraft makers

I've helped build aircraft.. quite familiar with the various build options, but you may have noticed, boats travel on water not air. Let's not compare apples to bananas

If carbon was the same cost as glass, most boats would be made from carbon. But you go ahead and build in floppy fiberglass. That was not the question 

 

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Seems everyone wants to argue fiberglass is better than carbon, rather than answer the question. I already have access to carbon and ...

"19mm H80 foam 1.5 kgs per sq m,with average of 450 gsm carbon (1.8 kgs/sq m) each side it would weigh (1.5+1.8+0.5 (wet out the foam) = 3.8 kgs per sq m. Replace the carbon with twice as much glass, it would be 1.5+1.8+1.8+0.5= 5.6 kgs/sqm. Difference on 126 sq m is 227 kgs..." 

but found the answer to my question. 1/2 x glass or thereabouts so will just use glass scantlings, thanks 

you can carry on convincing yourselves fiberglass is better 

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1 hour ago, Ryan.. said:
27 minutes ago, Ryan.. said:

you can carry on convincing yourselves fiberglass is better 

I think I’ll “carry on” convincing myself that it’s better to like… do actual engineering analysis on a 60’ cat design. 
 

but to each his own…

 

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9 hours ago, fastyacht said:

Setimrs y ou need to do some prelim eng desgn to beable to makr a useful wgt est.

Blowing smoke rarelyvworks. Unlesscyoi are Hunter S Thompson

Are you suggesting contacting an actual naval architect or engineer?:blink:

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I think he doesn’t want advice.
 

He just wants an audience to laud his innovative and unique approach to solving the age old problem of being shit flat broke and wanting what he can’t afford. 

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46 minutes ago, Sail4beer said:

I think he doesn’t want advice.
 

He just wants an audience to laud his innovative and unique approach to solving the age old problem of being shit flat broke and wanting what he can’t afford. 

Yah 

Carbon is a waste of money on a cruising boat 

properly compacted ,  properly selected , oriented  eglass fabrics  and properly cured resin will product a very light , strong hull , deck 

you are best advised to spend weight saving money on foam core interior components , carbon mast , synthetic rigging and molded sails 

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3 hours ago, slug zitski said:

Carbon is a waste of money on a

Instead of attempt to answer the question asked, idiots will make numerous assumptions about what you are thrying to do, and spew whatever dogma of the day the sheep are flocking to, providing no value to anyone except trying to make themselves feel smart 

 

 

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13 minutes ago, Ryan.. said:

... idiots will make numerous assumptions about what you are thrying to do, and spew whatever dogma of the day the sheep are flocking to, providing no value to anyone except trying to make themselves feel smart 

....and, in turn, noobs will make random ad-hominem statements about the people who tried to help but who, ultimately, have given you a forum to prove that you aren't smart enough to understand that informed answers have value even if you don't "like" them.

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17 hours ago, fastyacht said:

Okay then...so why are you asking? So far you have at least two nav archs involved here. I think there may be a third...but you definitely know better. Pics or it didn't happen.

if the flyin' hawaiian can make it 100 yards out of SF bay ,  I'm sure when Ryan's done, he can at least double that distance..

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1 hour ago, Ryan.. said:

Instead of attempt to answer the question asked, idiots will make numerous assumptions about what you are thrying to do, and spew whatever dogma of the day the sheep are flocking to, providing no value to anyone except trying to make themselves feel smart 

 

 

wow, so you want the members here to engineer your laminate schedule for free, and when you get an answer you dont like you turn into a proper cunt. awesome. has anyone told you to fuck off newbie, yet?

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11 minutes ago, Liquid said:

Is the OP also LongJohn?

Does the build include ama shock adsorbers?

I read that thread, and while LongJohn maybe a short stack short of a Denny's breakfast, he did not get as cunty as our boy here.

And as for the 'ama shock adsorbers', have a look at an old Formula 40 tri called Adrenaline....... http://trimarancool.blogspot.com/2009/10/adrenalin-is-pumping-again.html

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