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NOCALSAILOR

Best use of carbon for fast cruising cat

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Where are the most cost effective areas to use carbon in a cruising cat that wants performance, but does not have unlimited funds for a custom build.

 

i am guessing but 

1  main bulkheads/beams

2 chain plates

3 mast

4 Daggerboards 

4 rudders

Any thoughts

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27 minutes ago, NOCALSAILOR said:

Where are the most cost effective areas to use carbon in a cruising cat that wants performance, but does not have unlimited funds for a custom build.

 

i am guessing but 

1  main bulkheads/beams

2 chain plates

3 mast

4 Daggerboards 

4 rudders

Any thoughts

Get a good structural engineer. mast, beams and then daggerboards makes the most sense. Depending on budget, putting some in the hulls along the shear and keel line May work, as mentioned, get an engineer. 

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The choice of material is a very small fraction of a fraction of the total cost. For argument sake, let’s say the boat weighs 10,000 lbs. Of that, the structure is +/-30% of the total weight (3000lbs). Of that, about 50% is foam (1500lbs) and the rest is the skins (1500lbs). Of that, the best case scenario is ~1/3rd resin (500lbs) to fiber (1000lbs). Carbon is ~$20/lb. So...long story short...your cost for all-carbon construction is ~$20k. That’s nothing. A  10,000 lb cat would cost nearly $1m to build, so in other words the carbon represents about 2% of the total, and the E-glass or other wouldmt be free.

Interestingly, you don’t really save weight building in carbon. ISO regs and CE regs (I think) both require 1200gm/sqm regardless of material. A pound of feathers weighs the same as a pound of gold. You will have a stiffer boat, but not lighter. 

If I was building new I’d build the hull in E-glass, but not to save money or weight. The conductivity of carbon is a major PITA for a million reasons. That supports your ranking above, but for very different reasons. 

The early Gunboats were the fastest and were almost all glass  

 

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5 hours ago, NOCALSAILOR said:

Where are the most cost effective areas to use carbon in a cruising cat that wants performance, but does not have unlimited funds for a custom build.

 

i am guessing but 

1  main bulkheads/beams

2 chain plates

3 mast

4 Daggerboards 

4 rudders

Any thoughts

The best places for carbon are:

Max distance from the pitch centre so you save both weight and pitching.  ie, bowsprit, mast, forebeam, rudders, aft beam.

Anywhere that stiffness/strength is required with minimal thickness (daggers, rudders, mast).  

Where the material replaced is heaviest.  ie, carbon fittings instead of stainless steel, tow instead of bolts, etc.  

Carbon has never been cheaper.  With the savings in resin and reduced labour (assuming you don't need the 'look at me' effect of clear finished woven carbon), the cost difference is not high.

Soma,

Is that 1,200 gsm each side or 1,200 total?

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3 minutes ago, harryproa said:

Is that 1,200 gsm each side or 1,200 total?

IIRC it's outside only. Obviously you need a balanced laminate, so not much to be saved on the inside. I know designers have been tugging the authorities' shirtsleeves seeking relief but I haven't heard that the regs have been updated. 

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How does e glass or carbon in the main bulk heads affect the rigidity of a 48’ performance cat. For example, can a e glass boat fly a hull or does it need to be carbon. Please note I don’t think a cruising cat is flying a hull just a question of interest.

 

Soma some of the early gunboats are e glass do they have any carbon? If so what areas? Do they fly a hull?

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8 hours ago, NOCALSAILOR said:

How does e glass or carbon in the main bulk heads affect the rigidity of a 48’ performance cat. For example, can a e glass boat fly a hull or does it need to be carbon. Please note I don’t think a cruising cat is flying a hull just a question of interest.

 

Soma some of the early gunboats are e glass do they have any carbon? If so what areas? Do they fly a hull?

The early GBs were mostly glass with just the bulkhead reinforcements and structural reinforcements in carbon (and boards/mast/rudder/longeron in carbon obviously). They are the fastest, most hull-flying GBs out there. There ARE lots of cracks but virtually all cracks are just fairing. There have only been a few structural cracks and those were easily caught and repaired. 

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Mast, but built by somebody who knows what they are doing. Must be properly engineered and autoclaved to attain and justify carbon but done right, the advantages are significant.

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On 1/21/2019 at 8:10 AM, soma said:

The choice of material is a very small fraction of a fraction of the total cost. For argument sake, let’s say the boat weighs 10,000 lbs. Of that, the structure is +/-30% of the total weight (3000lbs). Of that, about 50% is foam (1500lbs) and the rest is the skins (1500lbs). Of that, the best case scenario is ~1/3rd resin (500lbs) to fiber (1000lbs). Carbon is ~$20/lb. So...long story short...your cost for all-carbon construction is ~$20k. That’s nothing. A  10,000 lb cat would cost nearly $1m to build, so in other words the carbon represents about 2% of the total, and the E-glass or other wouldmt be free.

Interestingly, you don’t really save weight building in carbon. ISO regs and CE regs (I think) both require 1200gm/sqm regardless of material. A pound of feathers weighs the same as a pound of gold. You will have a stiffer boat, but not lighter. 

This highlights one of several advantages of one off/owner building vs production boats:  the owner/builder is not bound by the ISO and CE regs and the production builder is.    

The Schionning G Force 12 is a racy cruiser bridge deck cat weighing 11,000lbs-5,000 kgs, so a 10,000lb cat would be 35-40' long.  

The G Force 12 base laminate is 600 glass each side which could be halved for carbon.  The Multi 50 tris (9,000 lbs) have 300 gsm carbon either side.  

A non ISO boat with carbon skins could have a quarter the base laminate weight of an ISO glass boat.  If the surface area is 250 sq m, the weight saved is 250 *(3.6-0.9) = 675 kgs/1474 lbs, (15% of 4,500 kgs/10,000 pounds) and outweighs any weight savings from carbon mast, beams, rudders, daggers or fittings.   The carbon laminate, including resin, is about $1,200 more expensive, more than offset by the smaller hulls, rig, motors, etc enabled by the weight saving.  

The regulations wind the design spiral upwards and everything gets heavier.    Which is why  'lightweight production cats" built to arse covering standards are heavier than cats designed according to the loads they will see (plus appropriate safety factors).

Nocal,

A performance cat with a cabin and full height bulkhead will not be noticably stiffer sideways whether the reinforcing is carbon, glass or wood as the beam is so high.  Those with the cabin behind the beam and a correspondingly low height will, at some height, benefit from carbon.   What this height is depends on boat weight, beam overall and mast compression.    

Hull flying engineering is pretty basic, and critical.  They should all fly a hull without noticable deflections or damage.  

Boardhead,

Mast building is no harder than boat building.    It is certainly  easier than building trimaran beams.  And the consequences of faiure are higher for the beam.     

 Infused carbon laminates have resin/fibre ratios of 30/70, effectively zero voids and allow plenty of time to accurately place the fibres, the same as an autoclaved laminate.    Modern infusion resins have properties near enough the same as prepregs, the carbon is the same for both.   Why pay for technology which does not produce a superior product?  

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I took Chris White for a fast sail years ago and he told me later that he thought selling a multihull to the public built to Skateaway's weight/performance would be irresponsible!!

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Peter Wormwood felt the same way when he started designing larger cats. He told me he laid awake at night just knowing some fool would flip one of his designs pushing too hard in a Gulfstream crossing in adverse conditions and it would haunt him forever. That sort of thing takes the wind right out of the most performance oriented designer in a hurry.

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harryproa,

I helped the new owners of a used 30' ShuttleCat re-rig and re-finish the carbon mast that attracted them to that particular boat. The 49' mast including standing and running rigging weighed 790 pounds, undressed the spar weighed 594 pounds!

My 58' bare mast weighs 243 pounds. With all due respect, the weight difference is astonishing. 

One atmosphere utilized in an infusion process will not compact the laminate as well as several atmospheres in an autoclave and a heavy, poorly engineered carbon spar is a waste of money.

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1 hour ago, boardhead said:

...he thought selling a multihull to the public built to Skateaway's weight/performance would be irresponsible!!

Selling supercharged Z06 Corvettes and Demon Challengers could also be considered irresponsible, but I'm grateful those choices exist, even if I'll never buy one. They push the limits!

I'm similarly grateful Randy Reynolds sold R33s, and I looked hard at buying one. It is truly a shame that the sailing world trashed the reputation of that boat based mostly on races with narrow boats.

The world needs designers who push the limits between responsible and irresponsible...  there's way more to learn still on high-performance multihulls, but if a designer wants to make money, it is easier to scale across a high-volume fleet of low-risk leaners where there's less left to be learned.

Viva le irresponsibilite!

Randii

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On 1/21/2019 at 1:58 PM, harryproa said:

The best places for carbon are:

Max distance from the pitch centre so you save both weight and pitching.  ie, bowsprit, mast, forebeam, rudders, aft beam.

Anywhere that stiffness/strength is required with minimal thickness (daggers, rudders, mast).  

Where the material replaced is heaviest.  ie, carbon fittings instead of stainless steel, tow instead of bolts, etc.  

Carbon has never been cheaper.  With the savings in resin and reduced labour (assuming you don't need the 'look at me' effect of clear finished woven carbon), the cost difference is not high......

^^^^^^^^ This. Especially the mast. Especially using vacuum bagging and autoclave etc.

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5 hours ago, boardhead said:

harryproa,

I helped the new owners of a used 30' ShuttleCat re-rig and re-finish the carbon mast that attracted them to that particular boat. The 49' mast including standing and running rigging weighed 790 pounds, undressed the spar weighed 594 pounds!

My 58' bare mast weighs 243 pounds. With all due respect, the weight difference is astonishing. 

One atmosphere utilized in an infusion process will not compact the laminate as well as several atmospheres in an autoclave and a heavy, poorly engineered carbon spar is a waste of money.

No argument about the engineering (I have spent a fortune on it over the years), or that a poorly built spar, or anything else, is a waste.  But on infusion vs autoclave, we differ.

Which of the following justifies paying 10(?)  times more for a prepreg mast than getting it built by the same guy who built your much more complex beams? 

The carbon and the void content (less than 1%) are the same,

The layout of the fibres can be done equally accurately,

Few, if any, mast prepregs (the materials used in autoclaves) have more resin than the 30/70 result of infusion,

Both resins are more than adequate, assuming both are post cured (which does not require an autoclave).

The fibres in the laminate are non compressible.  When they are all touching each other, more pressure achieves nothing.  2,000 lbs of force on a sq' of laminate will not compress it any more than 6 atmospheres/12,100 pounds.   Few mast builders use more than 2-3 atms.   Experiment:  Stack up 25 layers of 6" square carbon uni at various angles and put a piece of ply on it.  Measure the distance to the floor.  Drive your car onto it and measure the distance, it will be about half as high.  Then drive a truck onto it and measure the distance.  It will barely change.

Autoclave pressure ensures the heated resin is squeezed into the air spaces between the fibres, forcing out the air.  An infused laminate has no air in it, so the fibres are all touching as much as they can.  The resin fills the spaces as it advances.    

Autoclaving is easier to automate (the prepreg sheets are more or less rigid at room temperature) and does not require resin to be mixed.  These are excellent attributes if you do not have faith in your workers.  If you do, infusion is not only cost effective, but gives an equally light, stiff, strong product.

Interesting about your mast weight.  We built a 17.5m/58' carbon/glass mast (hand laid and vac bagged, not infused) for a 50' harryproa. Weighed 120 kgs/264 lbs, bare.    Weighed the same with all the standing rigging.  ;'-)  https://www.youtube.com/watch?v=8chR6DAFjGA

Not sure if you ever get to this part of the world, but if you do, it would be great to meet you.  I sailed a few miles, including a Hobart, on Verbatim/Bullfrog, which seems to have a lot in common with your tri.  

 

 

 

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Harryproa have ever seen the Schionning carbon wing mast? I have seen the plans for the single mould wing mast he has designed . I am wondering 8f you have any thoughts?

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10 hours ago, boardhead said:

harryproa,

I helped the new owners of a used 30' ShuttleCat re-rig and re-finish the carbon mast that attracted them to that particular boat. The 49' mast including standing and running rigging weighed 790 pounds, undressed the spar weighed 594 pounds!

My 58' bare mast weighs 243 pounds. With all due respect, the weight difference is astonishing. 

One atmosphere utilized in an infusion process will not compact the laminate as well as several atmospheres in an autoclave and a heavy, poorly engineered carbon spar is a waste of money.

 

3 hours ago, harryproa said:

The carbon and the void content (less than 1%) are the same,

The layout of the fibres can be done equally accurately,

Few, if any, mast prepregs (the materials used in autoclaves) have more resin than the 30/70 result of infusion,

Both resins are more than adequate, assuming both are post cured (which does not require an autoclave).

The fibres in the laminate are non compressible.  When they are all touching each other, more pressure achieves nothing.  2,000 lbs of force on a sq' of laminate will not compress it any more than 6 atmospheres/12,100 pounds.   Few mast builders use more than 2-3 atms.   Experiment:  Stack up 25 layers of 6" square carbon uni at various angles and put a piece of ply on it.  Measure the distance to the floor.  Drive your car onto it and measure the distance, it will be about half as high.  Then drive a truck onto it and measure the distance.  It will barely change.

Autoclave pressure ensures the heated resin is squeezed into the air spaces between the fibres, forcing out the air.  An infused laminate has no air in it, so the fibres are all touching as much as they can.  The resin fills the spaces as it advances.    

Autoclaving is easier to automate (the prepreg sheets are more or less rigid at room temperature) and does not require resin to be mixed.  These are excellent attributes if you do not have faith in your workers.  If you do, infusion is not only cost effective, but gives an equally light, stiff, strong product.

Just to add to the above comments, the key to infusion is that the reinforcement is fully compressed dry, and only low pressure is required to achieve this, then the minimum amount of resin fills the remaining gaps. This is straightforward to understand in a uniform laminate, but the real advantage is in highly tapered laminates because you can achieve real tapers which are optimally wetted out at the taper.

Achieving the same thing with prepreg requires that that the additional resin, which cannot be tapered, be removed, and this requires suitable temperature to reduce the viscosity, and high pressure to migrate the resin away into an absorption layer.

Hence both methods can give substantially identical final results, but with prepregs you MUST use high pressures and suitable temperatures, whereas this is not required for infusion. In fact, if infusion is done under high pressure, the laminate can end up dry in places.

The big advantage with prepregs is when using honeycomb cores. We've experimented using a bagged layer over the core then infusing on top of that, but more operations are required and it results in a slightly heavier laminate in the end with a secondary bonded interface.

Only other comment to the OP is that throwing carbon into a laminate is a waste of time if you haven't properly engineered the relative stiffness characteristics, otherwise you will just create failure in shear between layers with different stiffness characteristics. It's a good way of transferring load from the fibres into the resin, which is never efficient.

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On 1/20/2019 at 10:06 PM, soma said:

IIRC it's outside only. Obviously you need a balanced laminate, so not much to be saved on the inside. I know designers have been tugging the authorities' shirtsleeves seeking relief but I haven't heard that the regs have been updated. 

Why do the regs hold sway for what are largely one off customs?  Is it a liability thing, or the owner would not be able to insure, or...  No criticism intended.  Curious.

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24 minutes ago, Wess said:

Why do the regs hold sway for what are largely one off customs?  Is it a liability thing, or the owner would not be able to insure, or...  No criticism intended.  Curious.

I asked HH if they'd abandon the ISO regs and do a laminate that matched the structural requirements but not the ISO requirements. HH (and MM) said "no". I think they're struggling from legitimacy issues so they want to be legit.

I also advocated abandoning ISO for the Gunboat 68, but the French said "no". I asked if we could offer a non-ISO "regatta" version and similarly got a "no". In the case of the 68 I think they wanted to avoid any "thinking" on the floor, since they're "production" builders. My argument is that if you're buying a $7m boat you should get custom treatment. 

In both cases (HH & GB), the weight savings were equal or greater than going with prepreg/nomex (but staying ISO compliant) but meant less work and less cost. It's a no-brainer if you ask me. If I was going custom I wouldn't think of ISO. 

The only (sorta) counterpoint, we struggled to find insurance for the HH's. Insurers didn't want to insure "Chinese built Gunboat knockoffs" (their words, not mine). I tried to reassure the insurers that they were built to ISO but they didn't care. The Gunboats are also finding it increasingly difficult to find insurers. I don't think the insurers know or care that they are or aren't ISO, just that they are being sailed really hard and the insurers see a lot of claims. 

Lastly, no one in the HH/GB world are registering IN the EU and paying VAT. They're all foreign-flagged. So ISO isn't really required by anyone, flag state or insurer or anyone. So, a red herring that makes boats heavy unnecessarily. 

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harryproa

Who said anything about prepreg?  My mast was dry braided hi-modulus carbon over an aluminum mandrel. Back then (20 years ago) the next step was an external resin application, peel ply, absorbent media, membrane then high pressure and heat in the autoclave. I was told that resin would not cure in six months at ambient on the shop floor but in the autoclave would run like water through the filaments, compact and go rock hard - you need a rigid resin to keep the taught filaments in column for max compression physicals - easy to fully exploit carbon in tension, hard in compression and the mast section needs both. Today it's still a dry braid but the resin is infused and yields a better work environment, less labor time and a similar outcome. Resin/filament ratio is a function of the filament diameter and nesting in addition to the degree of pressure applied for resin extraction.

So I built the entire platform and foils in glass/vinylester with much thicker foam cores than commonly utilized then. Today I would go exactly the same route, there is no way that I could build that only piece of carbon in the boat - the mast - near to the stiffness/strength/weight achieved then.

We rigged the mast all synthetic as we had done the Gougeon "C" section it replaced (since 1997 and new on the block back then) and at age 65 I was still able to heft the dressed mast alone when we last stepped it. I recall taking a spirited ride up Buzzards Bay with Tom Bandoni on Biscuits Cantreau 3 under a 66' aluminum rig that Tom weighed at 900 pounds - ain't carbon great! Oh and Skateaway would have outrun that boat in those conditions but she was clocked at 38 kts in flat water with Jean le Cam driving and crew out on the fold out racks gaining leverage over and above her 35' beam.

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  That "irresponsible" boat I built has never suffered a single laminate fracture, anywhere and was built exactly to the structural design that I engineered and ran past Diab Barracuda from whom I purchased all the core material, the single largest material expense. Those materials of construction are still appropriate today.

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ISO compliant - I have no idea!

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43 minutes ago, boardhead said:

I recall taking a spirited ride up Buzzards Bay with Tom Bandoni on Biscuits Cantreau 3 under a 66' aluminum rig that Tom weighed at 900 pounds - ain't carbon great! Oh and Skateaway would have outrun that boat in those conditions but she was clocked at 38 kts in flat water with Jean le Cam driving and crew out on the fold out racks gaining leverage over and above her 35' beam.

That sounds crazy heavy for BC3's rig? Does that include all sails, etc?

My F40 (ex GAJ-Neptune) is an 86 boat but has the 87 mast section on it. At 7.6kg/m my 18.5m (60') section weighs 140kg (309lbs), but I can easily lift the mast, with rigging, diamonds, halyards, etc., so it can't weigh much more than that complete (I weighed the tip at 65kg with the base on the ground). Here is data for both sections:

 

86mast.jpg

87mast.jpg

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1 hour ago, soma said:

I asked HH if they'd abandon the ISO regs and do a laminate that matched the structural requirements but not the ISO requirements. HH (and MM) said "no". I think they're struggling from legitimacy issues so they want to be legit.

I also advocated abandoning ISO for the Gunboat 68, but the French said "no". I asked if we could offer a non-ISO "regatta" version and similarly got a "no". In the case of the 68 I think they wanted to avoid any "thinking" on the floor, since they're "production" builders. My argument is that if you're buying a $7m boat you should get custom treatment. 

In both cases (HH & GB), the weight savings were equal or greater than going with prepreg/nomex (but staying ISO compliant) but meant less work and less cost. It's a no-brainer if you ask me. If I was going custom I wouldn't think of ISO. 

The only (sorta) counterpoint, we struggled to find insurance for the HH's. Insurers didn't want to insure "Chinese built Gunboat knockoffs" (their words, not mine). I tried to reassure the insurers that they were built to ISO but they didn't care. The Gunboats are also finding it increasingly difficult to find insurers. I don't think the insurers know or care that they are or aren't ISO, just that they are being sailed really hard and the insurers see a lot of claims. 

Lastly, no one in the HH/GB world are registering IN the EU and paying VAT. They're all foreign-flagged. So ISO isn't really required by anyone, flag state or insurer or anyone. So, a red herring that makes boats heavy unnecessarily. 

Thanks.  Kinda what I thought.  And am just assuming that somewhere behind the curtain for the designer/builder is a lawyer saying it must meet a standard - and ISO is about the only one - to limit any liability downstream.  But pure guess on my part.  Can't think of any other reason they would keep doing this.  Its a PITA, but "industry" could come up with their own new standard...

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I never did the math but OK, based on your kg/m number we get around 260 for the bare tube to which you have to add cap, base, gooseneck, sheave boxes, spreader roots, spreaders, (very long with tip and intermediate diamonds), diamond cables, rigging screws, standing rigging,(all st.st.) halyards (Kevlar), rotator arm, clutches, winches and something I must have forgotten. Then there was the hydraulic ram equipped boom, anyway don't know if Tom included the (Kevlar) sails but am certain about the 900 pound #.

So my spar, fully dressed (no boom) weighs about the same as the bendy alloy tube, bare! With whatever all that weight was aloft BC3 pitched a hell of a lot more than she would carbon equipped. Ted Grosspart, her last owner was in the process of fitting a carbon rig when he, sadly' passed away a few years back.

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Amen.

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9 hours ago, boardhead said:

harryproa

Who said anything about prepreg?  My mast was dry braided hi-modulus carbon over an aluminum mandrel. Back then (20 years ago) the next step was an external resin application, peel ply, absorbent media, membrane then high pressure and heat in the autoclave. I was told that resin would not cure in six months at ambient on the shop floor but in the autoclave would run like water through the filaments, compact and go rock hard - you need a rigid resin to keep the taught filaments in column for max compression physicals - easy to fully exploit carbon in tension, hard in compression and the mast section needs both. Today it's still a dry braid but the resin is infused and yields a better work environment, less labor time and a similar outcome. Resin/filament ratio is a function of the filament diameter and nesting in addition to the degree of pressure applied for resin extraction.

This was a reason for an oven, not for an autoclave.    

If the outer circumference of the laminate when it was braided was, say 40" and it was then compacted further so the circumference was 39.9",  the non lengthwise fibres have no where to go so they kink, rendering them useless.  

Ted van Deeusen has god status round here and his braider is/was one of the 7 wonders of the composite universe.  But adding pressure to  -further- compact a male moulded tube (braided, filament wound or hand laid) during cure is a recipe for failure.   However tight it is wound, this is the maximum pressure that should  be applied.

Adding pressure to a laminate where all the air has been removed by vacuum will not squeeze any more air out, as there is none to squeeze.

These days, resins are near water thin at room temperature, so the oven is only needed for post cure, which is much lower tech than an oven required to make resin runny and cure it.  We infuse and cure masts at room temperature, post cure them in the sun.   Pre infusion,  curing required an insulated box, heater elements, high temperature mould and bag and a bunch of thermocouples.  

20 years ago, an autoclave was a good idea for a one off mast built in a female mould.    Now, the same result can be achieved with infusion, at a much lower cost, which contradicts what you said in post 13 and 16.

Filament diameter is irrelevant to fibre/resin ratios.  The best possible nesting is each fibre touching 6 others viewed in cross section.  This is equally likely/unlikely in a single tow of 6,000 filaments (braided) as it is in a length of unidirectional (50 tows laid side by side).  The difference in cross section area is that between a square and a circle of the same dimensions, regardless of what those dimensions are.  

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If you say so! My comments are based on what I have witnessed and been told by a successful mast fabricator. I have purchased five 50 to 60 foot spars built to my layouts, engineered by that fabricator, Composite Engineering. All have been successful.

I have also encountered some less successful carbon spars, mostly just heavier but also spars that failed, one is sat in my yard right now, built by a high end name brand and I am amazed at the lack of adhesion between the laminates and the fiber orientation, glad I did not pay for or own that one!

 You are arguing details that are outside my personal experience and I do not feel qualified to counter your conclusions so I will bow out of this one.

 Masts, in my opinion, justify the use of carbon better than any other component in a multihull. 

 If you want to talk about hull, beam, rudder or daggerboard construction I have experience there and reasons I would specifically not use carbon.

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On 1/20/2019 at 2:10 PM, soma said:

The choice of material is a very small fraction of a fraction of the total cost. For argument sake, let’s say the boat weighs 10,000 lbs. Of that, the structure is +/-30% of the total weight (3000lbs). Of that, about 50% is foam (1500lbs) and the rest is the skins (1500lbs). Of that, the best case scenario is ~1/3rd resin (500lbs) to fiber (1000lbs). Carbon is ~$20/lb. So...long story short...your cost for all-carbon construction is ~$20k. That’s nothing. A  10,000 lb cat would cost nearly $1m to build, so in other words the carbon represents about 2% of the total, and the E-glass or other wouldmt be free.

Interestingly, you don’t really save weight building in carbon. ISO regs and CE regs (I think) both require 1200gm/sqm regardless of material. A pound of feathers weighs the same as a pound of gold. You will have a stiffer boat, but not lighter. 

If I was building new I’d build the hull in E-glass, but not to save money or weight. The conductivity of carbon is a major PITA for a million reasons. That supports your ranking above, but for very different reasons. 

The early Gunboats were the fastest and were almost all glass  

 

I agree about weight savings. When I started building my F32 trimaran, I calculated that building from Farrier's recommended carbon layup compared to his recommended glass layup would save around 300 pounds, or perhaps 8% total displacement. Makes a difference for racing, but not for cruising, especially since there are so many other places in a cruising boat to save weight. When I switched from 10HP outboard to 6, and from lead acid batteries to LiFePo, my boat dropped 100 pounds.

While the material cost is similar, carbon fiber is far more expensive to work with. It doesn't get clear when wet, so it's hard to tell how much resin to use unless you've got a lot of experience. And you might as well not even bother if you're not vacuum bagging, which is still far cheaper than infusion. That kind of labor is not cheap unless you're doing it yourself.

But Nocalsailor pretty much nailed the list. My boat has vacuum bagged carbon beams, bulkheads, folding structure, daggerboard, rudder, chainplates, main hatch, bow, and galley countertop (just because it looks cool). All else is biaxial glass with vinylester resin. And some Bondo.

 

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6 hours ago, boardhead said:

 

 If you want to talk about hull, beam, rudder or daggerboard construction I have experience there and reasons I would specifically not use carbon.

Boardhead what would be your thoughts on not using carbon in the the bulkheads and beams on a 45-50 light cruising cat?

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Why would you do that when Eglass and vinylester resin would do the job just fine. There is a big difference between a light cruiser and a racer.

Boardhead’s boat has no carbon and at 40’ weighs about 5,600 lbs. There are no flaws in the structure after 27 years. His previous boat built in 1978 -also has zero structural flaws after years of use and neglect by later owners. 

Now you have me wondering what you are looking to build...

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On 1/21/2019 at 6:30 PM, harryproa said:

The G Force 12 base laminate is 600 glass each side which could be halved for carbon.

Seriously? 300 gm carbon in a hull? Great if you never bump a dock or hit a log. That is a very non impact resistant hull.

The underside of my bridgedeck was 1332 gm glass with pretty closely spaced top hat stiffeners and I never thought it was overkill. Hitting a lot of waves I thought it was just right.

 

Back to the original question:

- mast

- beams, especially if you are trying to reduce depth for cosmetic/accommodation layout reasons

- boards but only hidden behind a protective layer of glass for log impacts

- chainplates (because the fatigue #'s for carbon are a lot better than E-glass)

 

23 hours ago, Wess said:

Its a PITA, but "industry" could come up with their own new standard...

You have no idea how much haggling (and years of work) the ISO standards for yachts represent.
I do think the multi rules are overkill for structure but have never delved into them in depth.

Yes, if you're a production builder hoping to sell into EU, then building to ISO standards is a must.

On 1/22/2019 at 9:42 AM, soma said:

Lastly, no one in the HH/GB world are registering IN the EU and paying VAT. They're all foreign-flagged. So ISO isn't really required by anyone, flag state or insurer or anyone. So, a red herring that makes boats heavy unnecessarily

Not surprised, but an ISO standard build boat does give an underwriter something to hang their hat on before writing a policy. Do GB/HH have a history of big claims? Haven't heard anything about it.

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53 minutes ago, Zonker said:
On 1/22/2019 at 3:30 AM, harryproa said:

The G Force 12 base laminate is 600 glass each side which could be halved for carbon.

Seriously? 300 gm carbon in a hull? Great if you never bump a dock or hit a log. That is a very non impact resistant hull.

The GForce 1200 has a durakore stripplanked hull which explains the 600 g/sqm laminate

For a foam cored hull Schionning would require a thicker laminate, probably double. but closer to ISO standard anyway

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I am not experienced with resin infusion but I am experienced with vacuum back filling, which what resin infusion basically is. From what I have seen resin infusion is done at 10-50 millibar layup pressure. That means 1 to 5% of the air is still  in the laminate with no way to remove it so 1 to 5% of the resin is air bubbles. That assumes the vacuum is uniform though out the layup. Which is difficult and if you are not real careful it is easy to have semi trapped air bubbles.

Am I missing something 1-5% void fraction in the resin is pretty big. On prepreg I would expect 0.5% voids in the prepreg and 2-3% in any added resin, with a 1 atm vacuum bag

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1 hour ago, nyker said:

The GForce 1200 has a durakore stripplanked hull which explains the 600 g/sqm laminate

For a foam cored hull Schionning would require a thicker laminate, probably double. but closer to ISO standard anyway

Another Data Point. My own , self built Tennant,  12 meter Bridgedeck cat,  1 x 440 DB each side of 12mm H80 foam plus  1 x 225 csm on the outside

only to take the point loads. Poly  blue resin through out..

Boat now 20 years old  , many ocean miles later and standing up well.

Wouldn't go heavier if I did it again.

 

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It is true that the basic structural carbon skin thickness on a foam cored multihull is too thin and fragile to survive the impacts, abrasion and permeation challenges associated with numerous elements of the structure.

The improved stiffness qualities are also of questionable value.

Why would a laterally flexing daggerboard be a problem - we are trying to match the lift/drag properties of the flexible foils attached to sharks and whales!

Certainly the vertical flexure of the glass reinforced beams on a trimaran is no big deal, actually absorbing a good deal of both the rig and righting shock loads.

I have seen way too many carbon rudder shafts shear and built alloy shafted replacements that were lighter, less expensive and more dependable. Maybe the carbon shafts were not done right but they were original equipment on quite new boats.

Bulkheads - one of the advantages of designing and building your own boat is that you can avoid building poorly conceived structures. Its pretty easy to include extremely light glass skinned bulkheads if you are not making outrageous structural demands on them. Let them be bulkheads!

Sprits - If anybody can put a lighter carbon than the anodized alloy pole out front on my boat I stand to be impressed!

Guard rails - you only have to inspect the exploded shards of one failed carbon tube to stay with malleable stainless or alloy - that rig is supposed to keep you on board - not disembowel you

Chainplates - fine but uni glass works great too,

Masts - certainly.

Booms - expensive for small weight gains.

I will qualify all of the above with my personal experience on boats under 50' length, the huge loads and weights involved in larger structures are out of my league but, realistically, also outside the majority interest in this blog.

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20 minutes ago, boardhead said:

Sprits - If anybody can put a lighter carbon than the anodized alloy pole out front on my boat I stand to be impressed!

Really? https://gwcomposites.com/carbon-tubes/

Pultruded carbon tubes / 6061-T6 alum compare properties.

Tensile =  1650 MPa / 310 MPa

Flex modulus = 1370 MPa / 69 MPa

Density = 1500 kg/m3  / 2700 kg/m3

Those are huge differences in the properties you really care about (strength, especially stiffness and weight). When you see these you see why carbon is so favored. There's a reason Boeing isn't building 777 wings in aluminum any more.

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Yeah, I know about 777 wings and 787 all over aerospace carbon and of course the benefits there are huge (did I read 40% lower fuel consumption for the 787?) but we are talking small structures here and I like affordable and available. Your source has "1/8" to 3/4" diameter stock"  the big stuff up to 46" long for only $23.63 - gonna look pretty silly on a 40 footer with an 1800 sq ft chute - might not make it.  OK - I am messing with you but the appropriate size is probably not stock and expensive, like a big deal just finding out.

So back in the real world I see overly thick walled carbon tubes poorly mounted with poorly aligned loadings right where light weight is important - in front of the bow. By placing the tube exclusively in compression you can get the job done with very light tubing and, once again, pushing the envelope, the wall is getting down to a rather skinny laminate - then there are the end fittings which would be included in that weight.

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I was a bit curious about these hull panels with thin skins so I looked up the Volvo 70 rules.

Minimum topsides (300mm above WL and above) = 7.4 kg/m2 not including paint and fairing.

So assuming a balanced laminate, and 25mm thick 80 kg/m3 foam,  that's 2 kg/m2 for foam and about 2.7 kg/m2 for laminate each side. In carbon.

Say 35% resin, 65% carbon = ~1700 gm/m2 carbon. (Got to leave a bit of weight to wet out the foam or a layer of film adhesive if pre-preg.)

Now a 70' mono bashing in the Southern Ocean at 40 knots isn't a 40' cat that is just sailing along in the teens sometimes. This is just another data point to consider.

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So less paint and fairing that's basically 1.5 (1.513) pounds per square foot on the Volvo.

With 3/4' (19mm) core, E glass and vinyl-ester skins, my 40' tri hull laminate is 1.3 pounds per square foot faired and painted but that's considered irresponsible by some, the amas are the same skin laminate but with 5/8" core, a hair lighter, decks average 1.2 pounds sq. ft. Around 2960 pounds bare platform, 5600 sailing, no cracks or deformation at 27 years old. No reason to build heavier.

For comparison my St Francis 44 is 3.4 pounds sq.ft. deck panel weight with 3/4" Airex core with glass roving/csm/poly-ester skins, after I ground off all the gel coat outside and CSM inside, painted inside and out. The boat is 16,000 pounds on the crane, dry tanks, floats 5" higher than when I bought it before putting near as many hours into the  renovation as the tri took to build. Production boat, well respected, multi circumnavigation history, working for me.

More data points.

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Cool. It's interesting in my engineering world that most areas I can think in bilingual units but not in others.

For composites, since all my work was in metric I can easily understand 7.4 kg/m2 and say that's heavy. But I cannot think in US units intuitively.

For stress I know what a proper answer will be in MPa or psi. Same with pump flows in GPM or m3/hr.

For HVAC work I totally know how much 800 CFM is but have no feel for 1.5 m3/second.

I've got friends with a St Francis 44 too. I shall tell them to get out the grinder and emulate you. But I fear that they shall live aboard that boat at the dock forever and maybe never leave until they are retired.

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I was born and educated in Brit when decimalization was happening, moved Stateside and welcomed a return to imperial so think that way with laminates, my professional background is in hydraulics, pumps, but my obsession is in multihulls.

I really like the St Francis at this point in my life but can't imagine anybody being crazy enough to grind the worthless filler and crap off the entire exterior and interior, keel to deck head the way I did, should have bailed right after I bought the boat but was determined to make it work. Mine is # 007, later models were built to a higher quality but she does have a fabulous, very light bright wood interior, over 100 doors, so massive storage. The boat sails quite swiftly, realistically our cruising speed is not that far off Skateaway but involves much more motor sailing, maybe six fold the fossil fuel consumption, and thats just running the leeward motor only.

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What design is this for? 

 

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20 minutes ago, SeaGul said:

What design is this for? 

 

I am looking at some of the Aus designs like Bob Oram or Grainger. I am sure the designers know where to put different materials within the hull, but I am not ready to get that involved or take up their time.

More just planning out the best places to put effort and money.

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8 hours ago, Zonker said:

I was a bit curious about these hull panels with thin skins so I looked up the Volvo 70 rules.

Minimum topsides (300mm above WL and above) = 7.4 kg/m2 not including paint and fairing.

So assuming a balanced laminate, and 25mm thick 80 kg/m3 foam,  that's 2 kg/m2 for foam and about 2.7 kg/m2 for laminate each side. In carbon.

Say 35% resin, 65% carbon = ~1700 gm/m2 carbon. (Got to leave a bit of weight to wet out the foam or a layer of film adhesive if pre-preg.)

Now a 70' mono bashing in the Southern Ocean at 40 knots isn't a 40' cat that is just sailing along in the teens sometimes. This is just another data point to consider.

FWIW, Dave Gerr in his book “The Elements of Boat Strength” gives a speed adjustment to bottom laminates of 1% increased thickness for every knot over 10 knots.....

A good read if you are contemplating building a boat yourself....

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The "laminate reduction program" boat is a St Francis 44 designed by Angelo Livranos. My particular example left the factory as a shell and was finished by a well read but first time multi owner who employed a talented carpenter to build the interior and equipped her with everything including AC and a washing machine in the cockpit - too much for a 44 footer.

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On 1/23/2019 at 5:43 PM, wjquigs said:

While the material cost is similar, carbon fiber is far more expensive to work with. It doesn't get clear when wet, so it's hard to tell how much resin to use unless you've got a lot of experience. And you might as well not even bother if you're not vacuum bagging, which is still far cheaper than infusion. That kind of labor is not cheap unless you're doing it yourself.

I agree about the wet out, disagree about the cost.  Carbon has never been cheaper, and combined with the smaller amounts required and the resin savings, there is not much in it compared to glass.  

Why do you think infusion is more expensive than vac bagging?  For infusion you use a little more than half as much resin and do not need a bleeder fabric or perforated plastic.  You do the entire laminate in one hit rather than bagging the inner skin, bonding and bagging the core, then bagging the outer skin.    You do not have the mess of applying the wet resin, nor the rush of getting the bag on before the resin cures.  

With infusion, all  the materials are accurately placed on the mould, then the plumbing and the bag, none of which is time critical.  Once you have a 100% seal, mix the resin, place the hose in it and open the tap.  40 minutes of watching later, the job is perfectly wet out with exactly the right amount of resin and no voids.  

14 hours ago, Karlb said:

I am not experienced with resin infusion but I am experienced with vacuum back filling, which what resin infusion basically is. From what I have seen resin infusion is done at 10-50 millibar layup pressure. That means 1 to 5% of the air is still  in the laminate with no way to remove it so 1 to 5% of the resin is air bubbles. That assumes the vacuum is uniform though out the layup. Which is difficult and if you are not real careful it is easy to have semi trapped air bubbles.

Am I missing something 1-5% void fraction in the resin is pretty big. On prepreg I would expect 0.5% voids in the prepreg and 2-3% in any added resin, with a 1 atm vacuum bag

Why would you get lower voids from prepreg than from infusion?  The vac pump pulls the same pressure for both.  With infusion, it is pulling the air from the dry laminate which is a lot easier than pulling it through the prepreg resin.  And why would you pull 1 atm with prepreg and not with infusion?

Zonker, Emmelord,

If you have a lightweight cat, you treat it a bit more carefully than a heavy one.  You also increase the base laminate where necessary.  If 300 carbon on foam is sufficient for the 50' tris,  it is ball park suitable base laminate for a lightweight 35-40' cat which is what Soma was referring to.    

I did a lot of hard offshore race miles on XL2, a 38' Crowther cat,  built in 1986,  and still going strong, as are several sister ships.  The base laminate is 300 gsm/9 oz kevlar either side of 20mm foam.    

I have not seen any specs for the Schionning, was assuming it was the same as the heavier 40' cruisers which use Duflex panels, 600 glass either side of 19mm balsa or foam.  I would be surprised if Jeff has ever specified a base laminate of 1200 gsm glass either side of foam for a sailing cat.  When I was producing and selling Durakore, the veneers were assumed to be the equivalaent of 150 gsm of glass each side.  

Back in the 80's and 90's i was selling boat building materials in Aus, mostly to amateur builders, mostly designed by designers (Simpson, Chamberlain, Appleby, Crowther, Brady, Schionning, Grainger, Tennant, etc) who could not afford engineers to work out their hull laminates so they used experience (aka copying what the others did).   The usual hull glass laminate for a 40' cruising multi was 600 outside if it was high impact, 400 inside, 12 or15mm core.      No vac bags, cedar for ease of building or foam on frames for the serious weight savers.   I have never heard of one of these failing.    Mrs Octopus's boat is from this era.  

Pretty sure the V70 topsides were 40mm thick and doubt they were H80.    Nomex or H200 is  more likely.  They were allowed to use higher than standard modulus or strength carbon as well.    Any idea what the ORMAs are?

Another 2 data points:  

Harryproa 65' lee hull, engineered laminate (incl FEA), 800 gsm infused glass either side of 30mm foam (spec was 25, but it is being built and sailed above the Arctic Circle so insulation was important)  100 sq m of hull, 5 kgs per sq m/1.02 lbs per sq'.    

Harryproa C50.  600 gsm infused glass either side of 20mm foam  3.6 kgs/sq m /0.73 lbs per sq'.  

 

 

 

 

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Stupid Ronald Reagan. The US was ready to convert to metric  back then. Reagan killed it. Absolutely terrible price was and is still being paid.  Bcause along came Japanese cars and got metric into USA anyway.  It's not Americans' fault.

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But thanks to him I now have a set of tools for both!

My 1976 Toyota Land Cruiser introduced me to dual measures.

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4 hours ago, harryproa said:

 

 

Why would you get lower voids from prepreg than from infusion?  The vac pump pulls the same pressure for both.  With infusion, it is pulling the air from the dry laminate which is a lot easier than pulling it through the prepreg resin.  And why would you pull 1 atm with prepreg and not with infusion?

Prepreg is normally made using rollers than can generate very high pressure, which they use to compact the layup and remove bubbles. The supplier provides a spec with void fraction. You do not pull resin through prepreg. You cut and lay prepreg in the mold and then you sometimes add resin and/or cloth to special spots. Next you vacuum bag to compress the layup and squeeze excess out resin. The vacuum bag is 1 atm unless you have an autoclave  which can give you 5 or more atm.

The void fraction in prepeg is determined by the supplier and is low, normally under 1%

The void fraction in infusion is determined by what percentage of the air you remove. If you pull an infusion layup down to 10-50 millibar before you start the infusion and you keep the layup compressed, 1-5% of what should be resin, is air bubbles. plus that 10-50 millibar is at the gauge tap. The pressure can be higher, in spots if you don't do a good  job and you can end up with a much higher void fraction. Since bubbles are normally trapped  where the layup threads touch, that joint will be dry. That is bad.

With a single bag infusion you lose the vacuum bag effect of compressing the layup, as soon as you add all the resin. To keep the layup compressed, you add a second bag  over everything to act as a vacuum bag.If you don't have a 2nd bag and you pump or gravity flow the resin, you can put too much resin in.  I have never seen an infusion autoclave so the vacuum bag pressure is 0-1 atm.

The void fraction of infusion is determined by how much air you remove and how well you handle the details. there are also other issues, like resin vapor,  than can produce voids

 

My original question still stands, the void fraction for infusion looks like it will always be higher than prepreg, am I missing something?

 

 

 

 

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9 hours ago, Sidecar said:

FWIW, Dave Gerr in his book “The Elements of Boat Strength” gives a speed adjustment to bottom laminates of 1% increased thickness for every knot over 10 knots

Dave Gerr should be taken with a large grain of salt... especially that book.

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6 hours ago, harryproa said:

If you have a lightweight cat, you treat it a bit more carefully than a heavy one

Sometimes the world doesn't treat you as well as you might like!

Logs, being banged into with a heavy solid glass boat when being boarded for officials in some third world country. There are lot of things out of your control.

6 hours ago, harryproa said:

Pretty sure the V70 topsides were 40mm thick and doubt they were H80.    Nomex or H200

I'd believe the thickness but not H200 core except maybe in the slamming area forward of the keel close to centerline. They were allowed to use Nomex so everybody would have used it.

Rule is here if you want to read it:

https://www.volvooceanrace.com/static/assets/content/media/files/m7462_volvo-open-70-rule-v3-including-amendment-5.pdf

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Found this article that spells out a lot of the construction details on VO70's.

yes to 40mm core

yes to Nomex 

https://www.materialstoday.com/composite-applications/features/technology-dominates-volvo-ocean-race/

I did know about how tough it is to get good adhesion to nomex honeycomb and the use of a film adhesive layer (uh, like a pre-preg glue layer wihout any fiber that goes on dry but melts at temperature)  but didn't know of the technique of pricking the carbon skins to allow air out of the honeycomb cells.

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We know that spot patching carbon also creates load spikes at the edges and in the affected areas. Does it make sense that areas that are already load concentration points (i.e. beam-hull connection points) benefit from carbon there or is it better to just go with heavier, better glass reinforcement feathered out? I replaced carbon patches on a glass/airex build that were cracked with s glass uni thick patches and have yet to see any cracking, though time may tell a different story.

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I guess there a lot price difference between pre-preg carbon and "dry" carbon -  pre-preg more expensive - what could be a faktor -in a typical hullside composite laminate?

Must be easier to work with dry materials?  

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6 hours ago, Karlb said:

The void fraction in infusion is determined by what percentage of the air you remove. If you pull an infusion layup down to 10-50 millibar before you start the infusion and you keep the layup compressed, 1-5% of what should be resin, is air bubbles. plus that 10-50 millibar is at the gauge tap. The pressure can be higher, in spots if you don't do a good  job and you can end up with a much higher void fraction. Since bubbles are normally trapped  where the layup threads touch, that joint will be dry. That is bad.

With a single bag infusion you lose the vacuum bag effect of compressing the layup, as soon as you add all the resin. To keep the layup compressed, you add a second bag  over everything to act as a vacuum bag.If you don't have a 2nd bag and you pump or gravity flow the resin, you can put too much resin in.  I have never seen an infusion autoclave so the vacuum bag pressure is 0-1 atm.

The void fraction of infusion is determined by how much air you remove and how well you handle the details. there are also other issues, like resin vapor,  than can produce voids

 

My original question still stands, the void fraction for infusion looks like it will always be higher than prepreg, am I missing something?

DISCLAIMER: I know nothing about infusion but I am willing to be educated.

DISCLAIMER #2 : be warned... I am an engineer...

I must be thicker than infusion epoxy, because I do not understand your claim that the amount of air left in the layup is directly proportional to the vacuum you pull.

It is directly proportional to the volume of air you left behind, agreed, but this is not (necessarily) pressure differential related.

 

Why do you pull a vacuum? My understanding is that it is first to compact the fibers, so you increase your final fiber to resin ratio, and second to draw the resin through the fibers.

On the second point, everything else being equal, the level of vacuum will only have an effect on the time it takes to fill all voids; i.e. the speed at which resin will flow through the fabric. I guess one of the key goals is to make sure that you flow resin through the complete composite and leave no dry pocket behind. So the layout of inlets ports for resin and vacuum ports must have been an art, becoming a science with simulation software to figure out where to place which port. Right?

But if your layout of inlets and outlets is correct and leave no "dry pocket" or "dry micro pocket" behind (tiny bubble of air stuck to fibers? maybe?), I don't see why air left behind is related to amount of vacuum.

In other words, if you had a VERY weak vacuum (half an atmosphere), pulling in a VERY thin resin (very low flow friction losses) and very long cure time, there is no reason that the slow moving interface between air and resin would not eventually displace all the air and replace it entirely with resin.

Yes, you would end up with a much lower fiber to resin ratio, I understand the argument of the second bag that you put under vacuum to maintain the squeeze on the layout and maintain the high fiber compactness.

 

What am I missing?

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On 1/23/2019 at 8:17 PM, Karlb said:

I am not experienced with resin infusion but I am experienced with vacuum back filling, which what resin infusion basically is. From what I have seen resin infusion is done at 10-50 millibar layup pressure. That means 1 to 5% of the air is still  in the laminate with no way to remove it so 1 to 5% of the resin is air bubbles. That assumes the vacuum is uniform though out the layup. Which is difficult and if you are not real careful it is easy to have semi trapped air bubbles.

Am I missing something 1-5% void fraction in the resin is pretty big. On prepreg I would expect 0.5% voids in the prepreg and 2-3% in any added resin, with a 1 atm vacuum bag

I think your calculations are out regarding millibars. How do you pull a higher Vac on pre preg? 

Its easier to pull the air from a dry stack than it is prepreg, especially if you haven’t debulked at all the stages required. 

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On 1/23/2019 at 8:16 PM, nyker said:

The GForce 1200 has a durakore stripplanked hull which explains the 600 g/sqm laminate

For a foam cored hull Schionning would require a thicker laminate, probably double. but closer to ISO standard anyway

What density and shear properties does the durakore have? 

...... I’ll google it. 

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5 hours ago, Karlb said:

Prepreg is normally made using rollers than can generate very high pressure, which they use to compact the layup and remove bubbles. The supplier provides a spec with void fraction. You do not pull resin through prepreg. You cut and lay prepreg in the mold and then you sometimes add resin and/or cloth to special spots. Next you vacuum bag to compress the layup and squeeze excess out resin. The vacuum bag is 1 atm unless you have an autoclave  which can give you 5 or more atm.

The void fraction in prepeg is determined by the supplier and is low, normally under 1%

The void fraction in infusion is determined by what percentage of the air you remove. If you pull an infusion layup down to 10-50 millibar before you start the infusion and you keep the layup compressed, 1-5% of what should be resin, is air bubbles. plus that 10-50 millibar is at the gauge tap. The pressure can be higher, in spots if you don't do a good  job and you can end up with a much higher void fraction. Since bubbles are normally trapped  where the layup threads touch, that joint will be dry. That is bad.

With a single bag infusion you lose the vacuum bag effect of compressing the layup, as soon as you add all the resin. To keep the layup compressed, you add a second bag  over everything to act as a vacuum bag.If you don't have a 2nd bag and you pump or gravity flow the resin, you can put too much resin in.  I have never seen an infusion autoclave so the vacuum bag pressure is 0-1 atm.

The void fraction of infusion is determined by how much air you remove and how well you handle the details. there are also other issues, like resin vapor,  than can produce voids

 

My original question still stands, the void fraction for infusion looks like it will always be higher than prepreg, am I missing something?

 

The void fraction in prepreg cloth is low, but in the laminate, it can be high as air gets trapped between the layers.  This air has to be pulled out through the other layers and resin.  Vacuum bagging each layer, or several layers, of reinforcement prior to cooking the overall laminate overcomes this.  It is a lot easier for air to get out of a dry stack pre infusion than a prepreg stack.   

You have not explained why you cannot get the same vacuum pressure with infusion as you do with prepreg?  Until you do, your question about voids can't be answered.    The resin that flows into a bagged infusion laminate has almost no air in it  and if it is degassed prior to infusion), it has none.  So the system is air free.  The resin that flows into the bag only fills the voids, there is no excess.  hence the prepreg levels of resin:fibre ratios.    Double bagging arguably gives better results, but not enough to justify it on a boat sized structure.  

Epoxy has no volatiles, so there are no vapor problems.  I have also infused vinylester, which does have volatiles, but never had any problems.   

Zonker,

Not sure 300 carbon will withstand idiots in solid boats any better than 1200 glass.  Both will delaminate.  

The need to prick carbon to let air out of Nomex shows how difficult it is to remove air from wet laminates, even if they are prepregged.   It also shows the problems of high heat to cure resins.  This also applies to foam.  There are alo major concerns about water vapour with prepregs as they are moved from freezer to room temperature.  If not resolved, the water turns to steam and messes with the resin and the bond.  A good prepreg shop is temperature and humidity controlled.  Room temp cures, infusion (the dry  bagging removes all the water vapour) and post curing is much more reliable.  And vastly cheaper.   

Apparently it is possible to get Nomex which is perforated through the cell walls.  The air travels sideways rather than through the pin prick holes which get blocked as soon as the resin starts to flow and/or the stack moves as it is being consolidated.

I thought the V70 slamming area was what we were talking about. Sorry for any confusion.

 If you are interested in some work, could you email me at harryproa@gmail, please.

Seagul,

Much more expensive, and much harder to work, for no real gain in the finished laminate, but a lot of benefits for QC.  Not an issue if you have a reliable builder.

Bruno,

Load concentrations happen with glass and carbon.  Feathering/tapering is the solution. The thicker the laminate, the easier the feathering, but it is equally critical.   Mixing materials in the same stress path is dangerous, as is discontinuities at high load points such as beam/hull connections.  We use glass for the off axis loads and carbon for the lengthwise loads on unstayed masts as the carbon resists the bending and the glass the torsion and axial loads.  works well.  Mixing carbon and glass in the lengthwise laminate would be a waste of glass.

Laurent.

Agreed, except for the counterargument.  Infusion uses the max vacuum possible.  More cannot be got.  Thick resin is to be avoided.

 

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On 1/23/2019 at 9:18 PM, MRS OCTOPUS said:

Another Data Point. My own , self built Tennant,  12 meter Bridgedeck cat,  1 x 440 DB each side of 12mm H80 foam plus  1 x 225 csm on the outside

only to take the point loads. Poly  blue resin through out..

Boat now 20 years old  , many ocean miles later and standing up well.

Wouldn't go heavier if I did it again.

 

Is that the hull laminate? How much internal structure do you have? That does sound very light for a hull of 40 foot that’s ocean going. 

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2 minutes ago, mad said:

What density and shear properties does the durakore have? 

...... I’ll google it. 

Durakore is standard balsa with 1.5mm luan skins running lengthwise.  Shear properties the same as balsa in a conventional laminate.  We also experimented with thinner skins of wood, glass and carbon and foam instead of balsa.  this was a while ago, I am not sure what the current standard is, but it is no big deal to get whatever you want, at least in Aus where ATL manufacture it, along with Duflex panels, which are similar, but with laminate in both directions.

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On 1/23/2019 at 7:43 AM, wjquigs said:

I agree about weight savings. When I started building my F32 trimaran, I calculated that building from Farrier's recommended carbon layup compared to his recommended glass layup would save around 300 pounds, or perhaps 8% total displacement. Makes a difference for racing, but not for cruising, especially since there are so many other places in a cruising boat to save weight. When I switched from 10HP outboard to 6, and from lead acid batteries to LiFePo, my boat dropped 100 pounds.

While the material cost is similar, carbon fiber is far more expensive to work with. It doesn't get clear when wet, so it's hard to tell how much resin to use unless you've got a lot of experience. And you might as well not even bother if you're not vacuum bagging, which is still far cheaper than infusion. That kind of labor is not cheap unless you're doing it yourself.

But Nocalsailor pretty much nailed the list. My boat has vacuum bagged carbon beams, bulkheads, folding structure, daggerboard, rudder, chainplates, main hatch, bow, and galley countertop (just because it looks cool). All else is biaxial glass with vinylester resin. And some Bondo.

 

Infusion isnt any more expensive really, still got Vac bag and all the consumables, you have more wastage wetting out, even with a wet out machine, stress and worker exposure to the epoxy. 

Bag it up dry, with time on your side and shoot the resin in. 

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6 hours ago, Karlb said:

Prepreg is normally made using rollers than can generate very high pressure, which they use to compact the layup and remove bubbles. The supplier provides a spec with void fraction. You do not pull resin through prepreg. You cut and lay prepreg in the mold and then you sometimes add resin and/or cloth to special spots. Next you vacuum bag to compress the layup and squeeze excess out resin. The vacuum bag is 1 atm unless you have an autoclave  which can give you 5 or more atm.

The void fraction in prepeg is determined by the supplier and is low, normally under 1%

The void fraction in infusion is determined by what percentage of the air you remove. If you pull an infusion layup down to 10-50 millibar before you start the infusion and you keep the layup compressed, 1-5% of what should be resin, is air bubbles. plus that 10-50 millibar is at the gauge tap. The pressure can be higher, in spots if you don't do a good  job and you can end up with a much higher void fraction. Since bubbles are normally trapped  where the layup threads touch, that joint will be dry. That is bad.

With a single bag infusion you lose the vacuum bag effect of compressing the layup, as soon as you add all the resin. To keep the layup compressed, you add a second bag  over everything to act as a vacuum bag.If you don't have a 2nd bag and you pump or gravity flow the resin, you can put too much resin in.  I have never seen an infusion autoclave so the vacuum bag pressure is 0-1 atm.

The void fraction of infusion is determined by how much air you remove and how well you handle the details. there are also other issues, like resin vapor,  than can produce voids

 

My original question still stands, the void fraction for infusion looks like it will always be higher than prepreg, am I missing something?

 

 

 

 

The void content of a prepreg laminate is down the skill of the guys laying it up mostly, I’ve seen voids in a prepreg laminate over a mm in section. Can you post a link from any supplier that specifies the void content of the material and of a finished laminate? 

I’d be very interested to see this. 

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5 hours ago, Zonker said:

Found this article that spells out a lot of the construction details on VO70's.

yes to 40mm core

yes to Nomex 

https://www.materialstoday.com/composite-applications/features/technology-dominates-volvo-ocean-race/

I did know about how tough it is to get good adhesion to nomex honeycomb and the use of a film adhesive layer (uh, like a pre-preg glue layer wihout any fiber that goes on dry but melts at temperature)  but didn't know of the technique of pricking the carbon skins to allow air out of the honeycomb cells.

Its had its issues historically, but It’s not that difficult if you use the the right process. Spiking it has been done for 20 years in various spacing and size of spike. You can damage the cell walls of the nomex if you’re not careful. 

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1 hour ago, Laurent said:

DISCLAIMER: I know nothing about infusion but I am willing to be educated.

DISCLAIMER #2 : be warned... I am an engineer...

I must be thicker than infusion epoxy, because I do not understand your claim that the amount of air left in the layup is directly proportional to the vacuum you pull.

It is directly proportional to the volume of air you left behind, agreed, but this is not (necessarily) pressure differential related.

 

Why do you pull a vacuum? My understanding is that it is first to compact the fibers, so you increase your final fiber to resin ratio, and second to draw the resin through the fibers.

On the second point, everything else being equal, the level of vacuum will only have an effect on the time it takes to fill all voids; i.e. the speed at which resin will flow through the fabric. I guess one of the key goals is to make sure that you flow resin through the complete composite and leave no dry pocket behind. So the layout of inlets ports for resin and vacuum ports must have been an art, becoming a science with simulation software to figure out where to place which port. Right?

But if your layout of inlets and outlets is correct and leave no "dry pocket" or "dry micro pocket" behind (tiny bubble of air stuck to fibers? maybe?), I don't see why air left behind is related to amount of vacuum.

In other words, if you had a VERY weak vacuum (half an atmosphere), pulling in a VERY thin resin (very low flow friction losses) and very long cure time, there is no reason that the slow moving interface between air and resin would not eventually displace all the air and replace it entirely with resin.

Yes, you would end up with a much lower fiber to resin ratio, I understand the argument of the second bag that you put under vacuum to maintain the squeeze on the layout and maintain the high fiber compactness.

 

What am I missing?

The double bagging has been discussed for years, it does nothing for you. As you mentioned, it fibre to resin ratio you are trying to achieve. And a partial vac will only slow the rate of infusion and add resin. Not what you want. 

If you bag it properly and have a good seal, it’s a very good process. Just look at a monolithic glass panel at 5mm thick? If done properly, it’s absolutely pristine. 

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48 minutes ago, harryproa said:

Durakore is standard balsa with 1.5mm luan skins running lengthwise.  Shear properties the same as balsa in a conventional laminate.  We also experimented with thinner skins of wood, glass and carbon and foam instead of balsa.  this was a while ago, I am not sure what the current standard is, but it is no big deal to get whatever you want, at least in Aus where ATL manufacture it, along with Duflex panels, which are similar, but with laminate in both directions.

Thanks, I’ll still have to google it though to see what structural properties it has. Obviously higher density than regular foam core materials used. 

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Many interesting post here!

 

Treadstarter: You say you cant custombuild the boat - are you going to build yourself? Or buy stock? 

On a bridgdeck cat - it seems the building method will impact more on the weight that the use of carbon/not carbon. In areas like the rudders-daggers beams and mast - its a no-brainer to use carbon and infusion methods.

 

But are you using a mould or not - for the main parts? 

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9 hours ago, mad said:

Is that the hull laminate? How much internal structure do you have? That does sound very light for a hull of 40 foot that’s ocean going. 

Hull laminate. 

Very little.

Check out the cross sectional shape of that generation Tennant boats. Egg shaped.

2 meters between bulkheads. No stringers. 

If you want to see light , check out Aisa catamarans Stealth designs.

 

Hurricane-Stealth-11.8.jpg

LOA: 11.8 m

Beam OA: 6.45 m

Centreline Beam: 5.25 m

Displacement: 3,000 kg

Mast Height: 16 m

A bit of googling will turn up a load cell weight for Rating. Let us know what you find out.

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30 minutes ago, MRS OCTOPUS said:

Hull laminate. 

Very little.

Check out the cross sectional shape of that generation Tennant boats. Egg shaped.

2 meters between bulkheads. No stringers. 

If you want to see light , check out Aisa catamarans Stealth designs.

 

Hurricane-Stealth-11.8.jpg

LOA: 11.8 m

Beam OA: 6.45 m

Centreline Beam: 5.25 m

Displacement: 3,000 kg

Mast Height: 16 m

A bit of googling will turn up a load cell weight for Rating. Let us know what you find out.

I looked at the Stealth by Asia catamaran, but was told by a surveyor in Thailand that they are not up to the task of ocean crossing. THat could be his opinion. Either way hey are quite a bit lighter than some of the other boats love Oram or Schionnings.

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1 hour ago, SeaGul said:

Many interesting post here!

 

Treadstarter: You say you cant custombuild the boat - are you going to build yourself? Or buy stock? 

On a bridgdeck cat - it seems the building method will impact more on the weight that the use of carbon/not carbon. In areas like the rudders-daggers beams and mast - its a no-brainer to use carbon and infusion methods.

 

But are you using a mould or not - for the main parts? 

I am looking at infused flat panels with one of the Australian kits Oram, Schionning , or Grainger.

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On 1/24/2019 at 4:24 AM, NOCALSAILOR said:

I am looking at some of the Aus designs like Bob Oram or Grainger. I am sure the designers know where to put different materials within the hull, but I am not ready to get that involved or take up their time.

More just planning out the best places to put effort and money.

Designers wouldn’t mind you asking and they have the answers you are looking for based on the direction you want to go. Tons of useful info here thanks to your question!

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20 hours ago, Karlb said:

Prepreg is normally made using rollers than can generate very high pressure, which they use to compact the layup and remove bubbles. The supplier provides a spec with void fraction. You do not pull resin through prepreg. You cut and lay prepreg in the mold and then you sometimes add resin and/or cloth to special spots. Next you vacuum bag to compress the layup and squeeze excess out resin. The vacuum bag is 1 atm unless you have an autoclave  which can give you 5 or more atm.

The void fraction in prepeg is determined by the supplier and is low, normally under 1%

The void fraction in infusion is determined by what percentage of the air you remove. If you pull an infusion layup down to 10-50 millibar before you start the infusion and you keep the layup compressed, 1-5% of what should be resin, is air bubbles. plus that 10-50 millibar is at the gauge tap. The pressure can be higher, in spots if you don't do a good  job and you can end up with a much higher void fraction. Since bubbles are normally trapped  where the layup threads touch, that joint will be dry. That is bad.

With a single bag infusion you lose the vacuum bag effect of compressing the layup, as soon as you add all the resin. To keep the layup compressed, you add a second bag  over everything to act as a vacuum bag.If you don't have a 2nd bag and you pump or gravity flow the resin, you can put too much resin in.  I have never seen an infusion autoclave so the vacuum bag pressure is 0-1 atm.

The void fraction of infusion is determined by how much air you remove and how well you handle the details. there are also other issues, like resin vapor,  than can produce voids

 

My original question still stands, the void fraction for infusion looks like it will always be higher than prepreg, am I missing something?

Rob and Mad have answered most of this, but I add a little more:

1. The void fraction in each layer of prepreg is not the problem, it is air and water vapour trapped between layers as they are laid up. Each layer of prepreg is relatively impermeable until it is heated, so this is only extracted during consolidation, which must be at sufficient temperature and pressure to allow this. Skilled labour and controlled atmosphere can reduce this to a minimum.

2. The void fraction in infusion is not determined by how much air you remove during consolidation, but how much air is removed during consolidation and infusion. Since air flows through the compacted laminate much easier than resin, the remaining air is removed during the infusion process and replaced with resin, if the inlets and outlets are appropriately located and controlled.

3. The pressure in the bag is not changed by the infusion process to a significant degree. The resin is not flowed in using gravity or a pump, it is sucked in by the vacuum, and viscosity and flow control ensures that only a very small proportion of the vacuum is lost in the resin column, not enough to affect the consolidation. Using a second bag is a waste of time unless you want to recover this very small pressure differential, and if you do, then you have not set up the infusion correctly. I have personally never used one.

Regarding this third point, I have seen several people make the assumption that the incompressible liquid must destroy the vacuum, but this is not correct. The liquid may be incompressible, but it is still capable of having a pressure differential across it, as any liquid can, and you set up the infusion so the pressure differential between the supply (at 1 atm) and the bag (at 0.1 atm) occurs mostly in the tubes before the bag. This is achieved by ensuring that the flow rate potential of the vacuum pump is much higher than the flow rate of the resin supply. This differential also causes vapour in the resin to escape via the resin front, hence why vinylesters still work well with infusion.

Once resin is in the stack, it moves through by the small remaining pressure differential, but mostly by capillary action, aided by the sizing on the fibres, and this combination ensures that there aren't any dry areas even where fibres are pressed together. The capillary action is strong enough to ensure this, provided you don't have very high pressure applied to the outside of the bag, as noted earlier, which is why you don't see infusion in autoclaves. It is, of course, very slow.

Once the stack is fully wet-out, the resin supply is sealed, and the vacuum is maintained, so that the entire laminate is subjected to the full vacuum, and any lost consolidation is recovered, before the resin is set.

Regarding the comments about pricking the laminate to allow air to escape from the core, as Rob notes this is only problematic for high temperature post cure cycles, as during the initial cure the laminate is permeable. I'm not a fan of high temperature post curing other than for very specific applications, and you need to analyse your through-life performance to see if it is required for a given application. The biggest issue with high temperature cure is that the resin expands more than the fibres during the cure cycle (carbon actually contracts along its length as it heats up - a very useful feature for satellite structures) so then when the laminate cools the resin contracts and is then in tension - exactly what you don't want. This reduces the resin available strength, and can do so to a greater extent than the gain in strength due to the post-cure, so overall laminate strength is reduced. This can be particularly critical at structural geometries that rely on resin shear or laminate through-thickness strength, such as curved structures and out-of-plane joints. Foils are a classic example of this, and many of the failures we have seen can, I suspect, be attributed to this issue rather than poor design. This can be exacerbated by high autoclave pressures during the cure cycle, another advantage of infusion over prepregs.

This is an example of where designers must consider their structure, and not rely on manufacturers data for the resin performance. The manufacturers data is usually based on pure resin samples, and of course these will show beneficial property improvements with high temperature post-cure cycles, but this is not how the resin will necessarily be in your laminate. You need to perform a proper thermal structural analyses to determine if your application will see a benefit, and frequently this is not the case. We usually post-cure at 60 - 90 C maximum for most applications other than space components, as this is within the typical range of black-bulb temperatures that might be encountered terrestrially. Post cure needs to be longer, but we don't make high production volumes, so this is not an issue for us. Some resin systems do require high temperature cure to achieve usable properties, but we avoid using them unless the specific application will benefit.

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Great thread with a lot of knowledgeable folks weighing in. 

 

Does anyone have semi-accurate, empirical numbers for carbon pre-preg/nomex vs carbon infused/kerfed foam vs carbon infused/thermoform foam vs wet layup carbon/thermoform? 

We dug into the topic with the Gunboat 68 but I wasn't convinced we got accurate numbers to support our decision. The takeaway was prepreg/nomex wasn't worth it, kerfed core with infusion is HEAVY, and wet layup/vacuum was good but expensive with western labor. Infusion with thermoforming seemed to offer the best compromise. 

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Thank You,

The part that I was missing is, you run vacuum pumps all the time. The system I saw 20-25 years ago  either secured the vacuum pumps when they started the infusion or the pumps  "secured"  themselves when the disposable  filters clogged.  To  compensate  for the loss of vacuum,  they added gravity feed or a pump to the resin. Then, a second bag was added to prevent the layup from ballooning from the pressurized resin.

Also it stills appears  that there is lot of little details between an crappy  lay-up and a great lay-up

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4 hours ago, soma said:

Does anyone have semi-accurate, empirical numbers for carbon pre-preg/nomex vs carbon infused/kerfed foam vs carbon infused/thermoform foam vs wet layup carbon/thermoform? 

We dug into the topic with the Gunboat 68 but I wasn't convinced we got accurate numbers to support our decision. The takeaway was prepreg/nomex wasn't worth it, kerfed core with infusion is HEAVY, and wet layup/vacuum was good but expensive with western labor. Infusion with thermoforming seemed to offer the best compromise. 

Putting numbers to this would very much depend on the geometry, so the degree of curvature, and hence kerfing, you need to induce. Rob will have better info on this.

Personally I like nomex, either with prepreg or wet layup. Wet layup requires very careful control of resin quantity and distribution - you can very easily end up with flooded core or dry patches, but it is my preferred cost-effective approach, and if you are consistent you can achieve very similar results and, in my opinion, a better bond to the core with lovely fillets. The key is to saturate the laminate away from the core, then squeeze it consistently, before placing on the core, but time is against you so you need to be clear about what you can achieve in what time. The wet layup is flexible, so if you can chill the environment you can gain a bit of time. It can be a bit disconcerting because the resin absorption cloth stays dry, so you may think the laminate will also be dry, but if the absorption cloth is wet then the core will also be too wet. I don't think I would use a hollow core below the waterline on a cruising hull that spends long periods afloat.

I don't like the idea of kerfed core, not just because of the weight of the redundant resin, but also because the modulus of the resin and core are too different, leading to failure of the core along the lines of resin if the section is deformed. I appreciate that the kerfed core is used where curvature is sufficiently great that the panel has a high stiffness already, and I will say that I don't have experience of this (because I don't like it I don't use it).

Infusion with a formed core is, in my opinion, better than the "best compromise" - it isn't a compromise at all. You can achieve excellent laminate properties with near perfect core bonding, and produce complex shapes with the minimum of secondary bonding.

I would never make a structural laminate without a vacuum. It doesn't make any kind of economic or performance sense to me. You will save the cost of the bag in reduced resin usage, and then benefit for the life of the structure with the improved strength and reduced weight. I've done plenty of wet layup, no consolidation, laminating when I was a kid making windsurfers and catamarans, but never again.

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7 hours ago, soma said:

Great thread with a lot of knowledgeable folks weighing in. 

 

Does anyone have semi-accurate, empirical numbers for carbon pre-preg/nomex vs carbon infused/kerfed foam vs carbon infused/thermoform foam vs wet layup carbon/thermoform? 

We dug into the topic with the Gunboat 68 but I wasn't convinced we got accurate numbers to support our decision. The takeaway was prepreg/nomex wasn't worth it, kerfed core with infusion is HEAVY, and wet layup/vacuum was good but expensive with western labor. Infusion with thermoforming seemed to offer the best compromise. 

That’s pretty much all of it in a nutshell. 

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OK, since there is a wealth of knowledge pouring in, let me take advantage of it and ask a crazy question from a don't-know-nothing-amateur...

If, as an amateur, you wanted to build an unstayed carbon mast, knowing the technicality of dealing with infusion (never done it, so scared about it...), AND building over a plug (I would be scared to shit to NOT be able to remove the male plug from the finished cured mast once it is all set and done...), would the following construction method has any value?

  • Build the mast as two halves as strip planking of pultruded carbon strips: Toray Europe proposes T700 fiber strips 10mm wide by 3 mm thick, 12 m long standard. (I have NO idea of the price)
  • Glue the 2 halves together over a "double plating" strip.
  • Vacuum bag necessary layup of cross-weaved CF sock over it.

 

Flame away...

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55 minutes ago, Laurent said:

OK, since there is a wealth of knowledge pouring in, let me take advantage of it and ask a crazy question from a don't-know-nothing-amateur...

If, as an amateur, you wanted to build an unstayed carbon mast, knowing the technicality of dealing with infusion (never done it, so scared about it...), AND building over a plug (I would be scared to shit to NOT be able to remove the male plug from the finished cured mast once it is all set and done...), would the following construction method has any value?

  • Build the mast as two halves as strip planking of pultruded carbon strips: Toray Europe proposes T700 fiber strips 10mm wide by 3 mm thick, 12 m long standard. (I have NO idea of the price)
  • Glue the 2 halves together over a "double plating" strip.
  • Vacuum bag necessary layup of cross-weaved CF sock over it.

 

Flame away...

This may be very old school now (circa 1985) but is still relevant...  flat panels used on the sides.  Freedom 38 Wobegone Daze by Eric Sponberg:
https://www.ericwsponberg.com/free-standing-mast-designs/
https://www.ericwsponberg.com/wp-content/uploads/state-of-the-art-on-free-standing-masts.pdf

wood-epoxy-wingmast.jpg.1f353e9cccfcaf54339c58e9db7722b1.jpg Wobegone_Daze_3.thumb.jpg.895f4829efb2e392afa8fdeba763be1b.jpg

Wobegone_Daze_1.thumb.jpg.40d84bff43b7cd6bb613ca48f3f158d2.jpg

 

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13 hours ago, Laurent said:

If, as an amateur, you wanted to build an unstayed carbon mast, knowing the technicality of dealing with infusion (never done it, so scared about it...), AND building over a plug (I would be scared to shit to NOT be able to remove the male plug from the finished cured mast once it is all set and done...), would the following construction method has any value?

  • Build the mast as two halves as strip planking of pultruded carbon strips: Toray Europe proposes T700 fiber strips 10mm wide by 3 mm thick, 12 m long standard. (I have NO idea of the price)
  • Glue the 2 halves together over a "double plating" strip.
  • Vacuum bag necessary layup of cross-weaved CF sock over it.

 

Flame away...

Again, Rob is the man to advise you here, but from a structural perspective, your proposal could be made to work but would not be efficient, and you would want to provide some shear strength on the internal as well as the external face, otherwise the resin bond between the strips will fail on the "web" portion of the mast in bending, and the skin will then buckle as the bending stiffness of the section perpendicular to the length will be too low (almost zero, with your proposal). The only way around this is to make the outer sleeve sufficiently stiff and strong to overcome this, but this will then make the mast unnecessarily heavy.

I would offer two other points:

Firstly, don't be scared of releasing the plug. Use packing tape over the plug, then wax it, seal the mast end with a compressed air fitting in it, and stick the compressor on it.

Secondly, for a one-off, don't use a mould. Vac a flat panel onto a table, adjusting the laminate to give the bending stiffness where you want it, then bend the flat panel round into a teardrop shape. Tabs on the table will give you the overlaping bonding surface, which then provides the flat track mount. Once you have the shape, you can vac all the remaining UD and extra layers you need to the outside and around the joint. You'll need to fair the outside a small amount, but this is relatively trivial.

This produces a structurally efficient and aerodynamic shape easily and reliably. If the mast section requires internal structure, then this can be included when you bend the panel, and you can easily include halyard tubes or any other fittings with good access prior to closure. Not relevant to your freestanding mast, but if you want to add reinforcement, pulleys, etc. at the hounds, then you can bend the front of the mast into formers (bits of ply cut to shape), leaving the back open, do all the internal and external work at the hounds, and then close up later.

This method works great with cored sections as well. Just include spacers on the table where the core will go, then bond the core once the section is bent, with the outer skin on top.

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Hey nice way to build a one off mast. I like it. especially for an amateur build. Very little to go wrong.

I'll second the idea of not building a mast with strips of pultruded uni. No hoop strength or shear through the laminate.

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On 1/26/2019 at 2:09 AM, soma said:

Great thread with a lot of knowledgeable folks weighing in. 

 

Does anyone have semi-accurate, empirical numbers for carbon pre-preg/nomex vs carbon infused/kerfed foam vs carbon infused/thermoform foam vs wet layup carbon/thermoform? 

We dug into the topic with the Gunboat 68 but I wasn't convinced we got accurate numbers to support our decision. The takeaway was prepreg/nomex wasn't worth it, kerfed core with infusion is HEAVY, and wet layup/vacuum was good but expensive with western labor. Infusion with thermoforming seemed to offer the best compromise. 

The only people who think Nomex/prepreg are the way to build cruising cats are the the marketers, the materials suppliers and the 'my boat must be good, it cost a lot of money' crowd.  The materials costs,  high temperature moulds and chances of a screw up are not worth the potential, but often unrealised weight savings.  

Kerfing does not need to be heavy. The harryproa http://harryproa.com/?p=726 (see leeward hull) was kerfed on the inside of the foam exactly the right amount and extra resin was near zero.  The trick is to do this quickly and accurately, which requires some out of the box thinking.   

Wet layup/vacuum is likely to result in problems associated with rushing to get the bag sealed.    Plus ~half the resin ends up as landfill.   If the bag is sealed before the resin starts to gel,   it should end up a similar weight to a correctly set up infusion: about half the resin weight in glass, plus 1-200 gsm per side to wet out the foam.     The big weight, time and cost addition is when it cannot be done in one shot.   

Thermoforming foam takes a lot of time and energy, does not always bend correctly on the edges and may not conform exactly when it is bagged.  The resulting space gets filled with resin.     The weight if it does work properly should be the same as the infused or bagged resin.     In all cases, the better the vacuum, the less resin on the laminate.       It is much easier to get a proper vacuum with infusion as you have as much time as is required.      

These drawbacks are the reasons we developed Intelligent Infusion http://harryproa.com/?p=1845 and the harryproa hull shapes which use foam that does not require bending or kerfing or have conformity issues.  In many places, the foam does not even need to be accurately cut.     This increases the speed of build and reduces the effort considerably as it allows the entire half hull laminate to be simply infused in one shot and provides consistent, low resin:fibre ratios.  The time saved is ~50% over conventional build methods.  Waste is lower.   There is no cutting or grinding of cured laminates and no wet laminating, so it is less messy as well. 

 ..............

Anyone who can build a boat should have no trouble achieving 2/3rds the weight of an alloy spar for considerably less cost and vastly more fun using carbon.  

Unstayed masts are tapered in section and laminate, so premade strips are useless, unless you make them yourself.  When carbon was expensive I made an 11m unstayed mast using low cost tow in premade tapered strips, but it took a while.       Uni laminates need off axis material inside and out, and at various locations through the laminate that vary from 2-6mm of laminate thickness.   

Building masts in a simple  female half mould works well as long as you can get the inside joining layer(s) bagged in place.  This is not difficult, either wet and bagged or infused.   

The outer off axis layer should not be bagged as it will kink as the circumference decreases (see prev post).  I would not add material to the outside of a mast or mandrel for this reason.  If you use a sock for the outside (never for the inside, it will not conform), pull the ends tight, then wrap it from the middle with sti