Carbon Fiber Parts

I'm almost too scared to start this thread...

BUT I've been reading and looking at carbon fiber for making boats and boat parts...

The one guy told me carbon fiber is 5 times stronger than woven. Perhaps this is why it is so bloody expensive, because they know you're going to use 5 times less and have to make up for the bulk of what you would have spent... and then some

I have never worked with carbon fiber. The idea of being able to make light parts (and boats) is very attractive, and I saw a video on youtube of a cat where they claim they knocked another almost 50% weight off by, instead of using solid carbon, they used sandwitching to stiffen and strengthen the hull that way.

The boat does seem to sit on top of the water... and the sailor claims the boat feels very lively. https://www.youtube.com/watch?v=NDlTPTWUto8

Now the silly questions -

How stiff and strong is carbon ? !

Is it worth it to pursue carbon fiber or is it too expensive ? I was thinking if at all possible the rudder, dagger boards, beams and masts should be carbon fiber to make the handling parts lighter.

I'll be using vacuum injection, yip, I fixed the two vacuum pumps up. I had this method in mind and found a video that does exactly that, they call it serial infusion. https://www.youtube.com/watch?v=_J6SGZZolbU

Tell me everything you know.

Thanks.

 

A 6 ounce 50" yard of E 'glass is about $.50 at retail pricing. A 5.7 ounce, 50" yard of plain weave 3K carbon cloth is a bit over $40, full retail. The rest of the math should be pretty simple to work out Fanie. Of course you can get price breaks with larger quantity purchase. If you buy a full roll (100 yards), you pay in the $30 a yard range (retail).

 

Hello Par,

Yes the carbon is expensive. I can see doing calculations on the price will take up all 128 bits of my PC

Let's assume the price is not a problem, (like Alice in la-la-wonderland).

What's it like working with it and is it worth the trouble. or is it only for the rich to keep their boats faster than the rest ?

 

It's worth working with if you need (not want, but need) the weight savings. Simply put, most designs can't take real advantage of carbon, without a major redesign of the scantlings. Additionally, it makes absolutely no sense to use a high percentage of carbon, on a design that can't take advantage of it. As an example lets say you have a cruising yacht with a 32% ballast/displacement ratio with a conventional laminate. You elect to punch this up with a carbon laminate to get an impressive 50% ballast/disp. ratio, just to find out the boat heels less, but still can't go much faster, though possibly is more responsive, for 5 times the cost of the conventional laminate boat. This is an over simplification, but without price being in the mix, it's simply how much does this material bring to the design, as the effort to work it into a laminate is about the same as other fabrics.

 

I was thinking more along the lines of a mast for a trailable cat where you have to put the mast up and take the mast down for instance.

 

For starters, your not going to uses twill or plain weave carbon for structural scantlings.... Your going to use uni directional or Dbias type stitched fabrics... Uni directional is notably cheaper, although there's more work in laying the fibres in all the orientations required.

Is it worth it? Think about that for a minute... Phrases like "how long is a peice of string" come to mind... Come on Faine, I expected better from you

I looked into the scantlings for a large cat done in carbon, like a high performance type racer cruiser. The costs are certainly higher, but not as high ss I initially thought based on the price of raw materials comparing eglass to carbon. This is because there was less material required for the same strength, and less stiffeners required to get the required stiffness. Panel spans were greater, bulkheads and stringers further apart and less of them.

On a small trailerable boat, I doubt the weight savings would be substantial, as the panel spans are already very small, and the total quantity of material is quite small, let's say 100kgs for example. Done in carbon, you might be down to 85kg, a difference of 15kg. 15kg is less than a small esky with drinks and ice, so are you going to notice it? Unless your trying to win A-class, Probably not... On a larger boat, the difference might be 400kgs... More than the entire crew weight... So it becomes quite noticeable.

Is it worth it? If your trying to win races, then definitely yes. If not, then in my humble opinion, no it's not worth it, it's just too bloody expensive...

For a mast, yes it's worth it... You just can't get the stiffness you need in eglass without it getting ridiculously heavy and too much windage...

 

Masts are one of the few places where carbon is a substantial value without having to rework the boat. Even ignoring the absolute weight, reducing the difficulty in man handeling a mast is great.

 

A well designed tabernacle can eliminate the usual issues associated with raising and lower the stick. The Europeans and British have been doing this for generations and big, solid, grown masts can be lifted with a fingertip. In the states, tabernacles usually are weak and cumbersome, mostly just to make a trailerable boat, well trailerable.

The problem I see with carbon cruising spars, is the up front costs associated with them. Yes, in the long run you do save on rigging upgrades and change outs, but you pay for this up front. It's sort of like geothermal heating/cooling systems. Yes, you don't have a heating/cooling bill once it's installed, but when you look at the equipment and install costs, you've basically paid for all your heating and cooling needs up front. A 2,000 sq. ft. home might need a 4 ton A/C unit and a 60 KW of heat, for a total cost of say several thousand and a life span of 15 - 20 years, with $1,500 to $3,000 in yearly operations costs. The same thing in geothermal will run 30k to 50k to install and have a few hundred in electrical usage annually. It's the same money, but one is up front.

The only way I'd see a cruiser with a carbon (free standing) rig, is if I intended to own it for a couple of decades at least, if only to enjoy recovering some of these costs. I've only owned one boat for this long and I built it (back in the late 70's). I gave it away once, then got it back and now it's been gutted and converted from a sloop to a ketch, so it's enjoying a new life, but every other boat was eventually sold or busted up for it's parts.

 

There's also a learning curve for working carbon. Hand layups have a substantial performance penalty that are short of the published physical properties of the resulting laminate. There is less indication of when CF has been wetted out compared to glass. The fabric is stiff and is much harder to drape over compound shapes. Micro alignment of carbon tows in highly stressed areas is critical. Vacuum bagging or infusion is the answer but even then published values are usually not repeatable except in the most rigorous production environments. One way the amateur builder has to achieve CF's full mechanical characteristic is the use of CF poltruded rods providing they can be incorporated into the design.

Dino

 

Thanks Dinoa, what are CF poltruded rods ? and how is it used ?

 

http://www.marskeaircraft.com/carbon-rod-pricing.html
https://goodwinds.com/carbon/solid-round.html
http://www.cstsales.com/graphlite_data.html

A well known brand for poltruded carbon rods is "graphlite".
They are used for spar caps in aircraft, golf club shafts, windpaddle sail hoops, kite frames etc. They would be an excellent candidate for masts, spars, foils. The smaller diameters can take sharper bends. Because of the extremely high physical properties, +-5% when tested, the problem then becomes transferring loads to attachment points usually accomplished with large thick GRP pads that have a large bond line and generous bearing area for fittings.

Dino

 

Carbon

Fanie, you could buy a yard or less of carbon and a yard or less of e-glass and hand laminate(with epoxy resin) one layer to each side of a piece of 1/16"(4" X 12") balsa, wait two days and then try bending both pieces. I suggest this as a method of getting a "feel" for carbon. I use it exclusively for models and the difference in a models weight and stiffness with carbon is incredible-something you can actually feel.
I would be real hesitant in recommending that you try laminating a mast-very difficult to do well. There are threads in "design" and under "sailboats" that go into a lot of detail. And the forums resident expert in designing carbon masts is Eric Sponberg-you might talk to him after you read some of the threads and after you go to his website for mast info.Make sure to understand(ask Eric) how to protect a conductive carbon spar from lightning and what happens to an unprotected carbon spar. I would suggest pricing ready made carbon tubes for a mast to get a "feel" for cost and weight. You can check any supplier of carbon tube not just "mast" suppliers.
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I use 6k carbon tow* to make all kinds of carbon rods using silicone tube as a mold. You can make all kinds of curved or "bent" rods-I made a handle for a daggerboard(see below) once that was half the weight of an aluminum one. If you're interested in that kind of technique I can go into it in more detail-very simple and produces a high gloss exceptionally stiff and light weight rod.
* comes on a roll of lots of thin fibers bundled into a sort of string-easy to handle and easy to work with but the 6k tow, while being the least expensive from Aircraft Spruce and Specialty is around $80US for one roll. You could make probably 100 handles(below) for that roll.
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If you get into carbon there are some things that you need to know and incorporate in your shop. I use 5.7 oz woven carbon cloth for most everything and it's very easy to cut. But it takes a little practice to be able to hand laminate because you can't see thru it like you can with glass. And you know that glass is itchy when you grind it, well multiply that by 1.5 for carbon: you don't want carbon dust on your skin, in your eyes or in your lungs! Try to design a job so that the part is trimmed as part of the process-so no grinding-you can't always do that but it's worth it when you can.
When you work with carbon cloth or tow little "hairs" of the stuff tend to find themselves everywhere: you need to clean that stuff up every time on every job because carbon is conductive. Make sure it doesn't get in electrical sockets or electric hand tools. Little shards of carbon laminates about the size of a human hair can find themselves stuck in your hand ,fingers or feet if your clean-up is not thorough. Ask me how I know that(!)
All in all, in my opinion, carbon is Gods gift to boatbuilders and designers because of its exceptional properties. There are all kinds of techniques for maximizing the benefits of carbon but a simple single or double layer carbon laminate has outstanding properties just hand laid.
Good Luck!

Picture-carbon handle for a daggerboard pulltruded from 6k carbon tow in a silicone tube mold--click on image:

 

If one calculate the carbon fiber strength vs fiberglass woven of the same weight, what are one looking at ?
If the CF is 5 x stronger than WR, does it mean I can get the same strength from a 2mm CF than I would with a 10mm WR layup... ? or am I over simplifying ?

Thanks Doug, I like the carbon fiber more already It seems the 200g/sq m (5.7oz) is an all round favorite. You gave me some pointers where to look for some things.

I'll start with the smallest parts to get a feel for the carbon fiber and proceed to larger parts. It's amazing how many things one can suddenly think of you can do in a light material.

It seems the twirl forms fairly easy for odd shaped things, I understand the difference between uni and twirl.

I am busy designing a glass cutter that uses a round knife blade on a spring loaded arm, the blade is sitting on a car on a rail I can push back and forth, on a polypropylene sheet it makes the cutting simple, fast and clean, for rounds and so on I have a handheld one and last resort is scissors.

The link to that M32 cat, the dagger board seems very thin, and I must say I like it. Not sure why they curved it (to remain in the water when flying a hull ?) The rudder is going to be similarly thin and should slice effortlessly.

I will look into the lightning on a carbon mast, high voltage usually runs on the outside of conductors, but I guess the mast is hollow LOL so you can fit a hollow 50mm (2") copper cable in there... at least you won't see the burn marks on the inside of the mast as to the outside A direct lightning hit will disintegrate the mast.

At the price of the stuff one would probably collect every one of the little fibers and make something from it, not simply vacuuming it...

 

Building models is not the same building full size boats... Read again, WOVEN CARBON HAS NO PLACE IN STRUCTURAL SCANTLINGS! The woven and twill weave stuff is for cosmetic parts only ( and models). It's used for the visual carbon finish you get and it's drapability around complex little shapes, such as Doug's models.

I can build a stiffer and lighter part from eglass unidirectional fibers, compared to if I used woven carbon . They are chalk and cheese, and if you fail to understand why, then you need to do a lot more serious study before you go and blow your money on it...

 

Thanks Groper, I will keep that in mind. The uni strands have to be in the direction you want resistance and strength, in a beam you will have some uni's in the length to prevent bending and some at an angle both ways to resist twist. Then put a layer of twirl to make it look good.