Composite Tube Construction

Building a Carbon Fiber Forespar

After researching several ideas and building methods I’ve finally settled on a method and materials. The plans call for 6-foot long 4inch diameter aluminum un-stayed pole. 3 feet of the pole is inside the hull in a sleeve and the half is forward of the bow. Looking at several mast sections I found the wall thickness about 2.35mm I also find it easier to work in millimeters for the math.

Speaking with my NA the general rule of thumb is to go 30% over for Carbon if you do not want to spend thousands of dollars in mechanical engineering and testing. Simple math rounded up to 2 decimals gave me a 130% wall thickness of 3.06mm I went ahead and gave it a 150% factor of 3.53mm as my target wall thickness or .139-inch or just about 1/8” in a reasonable fraction. So I’m looking for a total lay-up of Carbon / composite of 1/8’” around a 3” - 4” molding surface.

I looked around for different type of material to build the mold such as aluminum, cardboard, foam, fiberglass, and PVC. The mold could be sectional several pieces, split two pieces, and solid - I thought about it a lot. I started to look for material and read all I could from others on tube building. I spoke to many people and each had their own idea some have built tubes and some have not, some have built boats some have not, some just like to give free advice and tell you how to do it they are the real jewels! But I listened to them all got to love it! The most enlightening conversion was with Kevin Cook on his method, wound fiber cord by hand and shrink tube. Written material was an article from West Systems here is a link to the article: http://www.epoxyworks.com/26/pdf/Building_composite_tubes.pdf I took a little from each plus my own spin. My final decision is a mold of a single piece of 3.5-inch schedule 80 PVC pipe. Schedule 40 is the type that you find at the local building supply stores - schedule 80 has thicker walls and you have to go plumbing supply houses to find it. Back to the math this pipe has an OD of 4 inches and a lay-up skin put me about 4-1/8 inches just about where I want to be. One reason for PVC is I usually never see Epoxy stick to unscuffed plastic.

I found a site www.sollercomposites.com/composites/carbon that sold the heat shrink tube and carbon sleeves like the “Chinese finger torture” toys. This is the material I decided to use to for my lay-up. I visited the site from my saved favorites and reviewed the supplies, then called and had a nice informational talk with the owner of the company. Looking at the tech sheet and my chat I had an idea of the size material to use, the stretch, fiber orientation, shrinkage, and ect…. I bought 30 feet of 5 inch Carbon sleeve that will give me 5 lay-ups plus more. I will be pulling the 5-inch diameter cloth down to 4 inches so it will "grow" in length up to 30% so I'll see what the real streach will be. I will have 1 lay-up of E-Glass on the outside for abrasion and impact to protect the Carbon. I also picked up 7 feet of the heat shrink plastic.

Now for the Lay-up I will make sure the tube is smooth and waxed with mold release. I will use a skin of the 3M film, then a thin lay-up of the 200 gram unidirectional carbon fiber most likely do two wraps and smooth it out with peel ply, then let it kick. Then I’ll give it a twist to see if it floats on the waxed PVC, if not I’ll cut the lay-up lengthwise and then it will twist. I’ll leave it on I just want to make sure it is not stuck. Once that is free I’ll be assured that it will not stuck to the tube. A light sanding and clean the blush then I’ll be ready to lay-up the sleeves wetting them out as I go. If I need a little more thickness I may do one unidirectional wrap in the middle of the sleeves Once it is wetted out I slip on the plastic heat shrink tube. Start heating in the middle and work my way out to the ends. The heat shrink tube acts the same as vacuum bagging. Each layer of carbon sleeve is rated at .53mm thickness the fiber sleeve is. 28mm. I figure I will get 5 – 6 layers of carbon and 1 fiber. I’ve ordered the composite materials I just need to pick up the PVC tube from the supply store now.

As usual I’ll take pics and post it on the web. I need to make the tube and sleeve for the tube with the Starboard side of the main hull as it gets molded into the hull. This will also be a test for the process because I need to make a 10’ boom and two 17’ connecting beams.

Later.

Your NA is conservative, "Black metal engineering" typically says design your part in ali and then replace with the same thickness of carbon (using equal layers of 0/90 and +/-45 degree fibres).

Yes I've heard that lay-up schedule before. I like the term "Black Metal Engineering" very cool!. Some parts such as struts, beams and rigging I'll allow conservative thinking. The hull skins and all seem to be right on perhaps he was shy on working rigging or knows I'm going to pound it.

I could see playing with that for a serious disposable racer based on an annual basis. Once I have molds built and things going I'd like to play some with some really light weight hulls ect....

What are some of the other rules of thumb for Black Metal? Another I always hear it to always paint it. I've seen carbon break down from the sun.

Hey all you marine engineers out there...

I've observed that the great majority (all?) of the spinnaker poles that I've seen on beach cats have circular cross-sections. I've also noticed that booms tend to have other shapes (oval, teardrop, rectangular), especially on really big boats.

Wouldn't a rectangular shape make a stronger spinnaker pole? If so, why isn't anyone using this, is it simply an equation of risk/reward (cost savings)?

Mike

Windage, complicated (out of axis) load paths and ease of construction to give just a few reasons.

I have built carbon fiber beams at home and had them built work. I have a couple comments.

I have had problems getting vacuum bagged composites to release when using a PVC pipe for a mold. It looks like they flow under pressure. My favorite mold is cardboard, the kind you can soak in water and then just peel away. For PVC pipe mold, I make my first layer glass. If I have trouble removing it I cut it lengthwise, remove it, splice it back together, then use it for a mold. Use minimum vacuum on the first layer of Carbon. After that it's strong enough to take anything.

I have used solarcomposites's finger puzzles. They work well. I find that after vacuum bagging, they are thinner than their nominal thickness. The void fraction of the fiber also depends on how far you stretch them. Basically, the more you pull them to reduce the diameter, the bigger the void. FYI I like hand wound. My favorite is 1/2 inch wide uni.

Do not drop below the percentage of carbon in your layup design
I would suggest at least 1 layer of kevlar near the middle. The purpose is prevent crack propagation. It will also hold things together if you crack your tube. Treat it as a core for strength calculations.

Good Luck, Have fun, Work slow so you can watch your work grow.

From 30mm dia and up I prefer to inflate a bag inside an aluminium tube that has been split in half and rejoined with hose clamps. Line the aluminium mould with packing tape and coat that with PVA. Blow the bag up with a compressor. Everything comes apart easily and the carbon tube comes out looking like a section of shiny black glass.
Under 30mm I coat aluminium tube in cadle wax and use it as a male mandrel. Once cured pour boiling water down the tube, the wax melts and and the mandrel is released.

Very good ideas thanks. I have what I think is a cool design idea for the beams an elliptical shape. Kind of like a fat flying saucer. I’m going to have a friend at work draw it out in Cad. Do you think cardboard is better then PVC? I want to be able to duplicate my work if I need to.

Couple of question any line on a supplier for cardboard tubes? Interested in the Air bag what do you use, any picture of the set-up?

I thought I read you were going to use carpet roll tubes for the roll. I guess I missed where that wasn't going to work?

Tex-

Yes you are right I didn’t know if anybody was paying attention enough to catch my flip on that idea. I was wordy enough so I zoomed past that idea. But now that you asked I found that the carpet rolls varied in diameter and wall thickness and it amounted to dumpster diving. I’m not beyond that but I had two other factors that changed my mind rather quickly:

1.What I need is to be able to reproduce what I make. If it was just a one-off tube no problem. Everything except the boom goes into sleeves - so if one was to break I need make a replacement to fit in the “built in” sleeves. If I use a process that is easily reproducible then when Mr. Murphy strikes it is more of a damn - then a full riot.

2. The shrink tubing available is 3.1-inch or 5.9-inch diameter currently the 4-inch size is not available and no date on the deliverable. Most carpet tubes seemed to be just around the maximum shrinkage limits of the 5.9-inch tube where the results could very and not always reliable - where “test it” is the recommendation. With the price of braided carbon tubing I did not like the “test it” option and followed the recommendations of the composite supplier. My design specifications of the plans call for a 4-inch forspar.

If I could find a good steady supply of 4” diameter cardboard tubes up to 17’ long I would go for it. The only option I found was to special order the tubes for a min of $900 set-up free plus a min order fee from a tube mill.

You can buy the bags but I've always just made them from plastic and packing tape. I'm sure there are much better ways but this has always worked for me. Vacuum bag material and the black stuff that you use to stick the vacuum bag material down would work too. Remamber to make the bag a little larger than the size it has to inflate to to make sure the mould takes all the load and the bag is just a seal.

how about pulling each end of the bag out of the tube, turning it back onto the outside of the tube, seal it to the tube and then vacuum the lay-up to the inside of the tube.

Paul
teamvmg.weebly.com

For a tube you might have to duplicate, I like Phil's methods.

But there are some questions you need to answer. If the outside of the tube is a critical dimension, build it inside a pipe. If the inside dimension is critical, build it over a mandrel.

I have used Phil's wax over aluminum tube except I use multiple layers of wax paper. I like wax paper because it's easy and I can build it up to a dimension, if I have to. I like aluminum because a 3 or 4 mm wall Al tube does not deform under the couple of psi of vacuum bagging. USE MULTIPLE SEPARATE LAYERS OF WAX PAPER. DON'T TAPE THE WAX PAPER TO THE TUBE, IT IS HARD TO GET IT TO RELEASE.

For vacuum bags I use nylon tubes from fiberglass supply company

I have not used the inside of a pipe method but, it is similar to what I have seen used. They started with a mandrel a foot or so longer than the mold. The mandrel was split into 4 or 6 sections with a pipe in the middle and held together with tape. They put a bag over the mandrel and then wound felt to about the right inside diameter. They wound release fabric over the felt and then put down their layout. They used 10 oz 45x45 cloth for the layup and it went fast. Two guys rolling epoxy on and 1 guy rolling the cloth. They wrapped the layup with stretchy film and clamped the pipe around it. Then they inflated the bag around the mandrel just enough to get the mandrel out. The mandrel is split with a pipe in the middle so if it's a bad day you can still get it out and you can vary the mandrel diameter by changing the diameter of the pipe. They inserted a heavier bag, positioned it and inflated it to about 5-10 psi. Then they popped the whole thing into an oven and waited. This was not a high tech setup. However they were very neat, clean, and carefull.

Is that what Farrier suggests?

Ingenious way to do it if 1 bar is enough pressure. Have you tried it the other way?

Paul your tube section is solid then?

With a vacuum you are limited to the pressure of one atmosphere = 14.7psi. With a compressor supplying pressure you are only limited by the strength of the mould and the amount of pressure your compressor can supply.

When you blow up a bag with a compressor the excess resin is squeezed out the join in the two halves of the tube mould. You can vary the resin fibre ratio to some extent with the amount of pressure that you choose to use. I have made tubes with a pressure of 50 psi but they tend to be a little resin starved. In the past I have found 35psi to be about right for my purposes.

Its just a PVC drainpipe so it can be cut with a grinder or Dremel - CAREFULLY!


EDIT; If fact, by looking at my own pic, I can see that I used a skill saw set to a very shallow cut.

What about casting wax ? As in calibrated lost wax castings. It comes in blocks, rods, film etc... It can be turned on a lathe to VERY precise dimensions, even possible to re-use it after melting. It is tough and can be shaped very precisely, it takes milling, turning thermoforming etc. Think about it if you want a CURVED spar. Anyone tried it ?

This is giving me some new ideas but I have more questions.

K I S S

Yep that is my thought all of the ideas look good. I think the heat shrink tubing is going to be a simple method for my immediate needs compared to the long range of the project.

How are you coming on your boat?

Filling and fairing. Fairing and filling!

My shoulders hurt!

Progress is on the website; teamvmg.weebly.com

I've done this on a smaller scale (1" OD) but used Latex tubing as the inflation medium. It's inexpensive, inflates easily, stretches a TON, the pneumatic fittings are very cheap, and epoxy doesn't stick (very well) to the latex tubing.

True and I agree 100%. Except, the vacuum has advantages with respect to removal of water vapour etc. The ideal is actually to do both (like the aerospace autoclave operators do). Create a vacuum and then apply additional pressure. This can be achieved in this case by putting your whole setup in a sausage back as well. The once everything is set up you "suck and blow".

Paul,
Do you mind giving a few more details on how you get the lay up and bagging materials set up in the tube?
Thanks,

I am also interested in more information on how you set it up.

Mike,
I understand your desire to make all the parts for your project, but this is the one part thats easy and relatively cheap to buy off the rack is carbon tubes. Its going to be highly stressed part, so it needs to be perfect, and you need to be weight sensitive because its hanging off the front of your boat. If you buy the beam tubes, the forespar and the boom, you would save on shipping.

Tubes are the one part I would BUY. Save yourself the headache and call Forte. www.forterts.com

You probably could find someone going south and have them strap it their roof racks.

+ 1
Makes perfect sense to me.

But thats the bit that kept me awake at nights trying to figure it out!

The trick was to wrap everything around a 2" mandrel [pipe] in reverse order [Starting with vac bag and ending with lay-up, poke it inside the 4" tube and then get it to stick/expand to fit. the 2" tube then is pulled out.

You can just see the 2" tube with the disposables already around it in the picture on the website.

I did it in about 3 hits because the pre-wetted carbon is very clingy and difficult to expand if too much is laid up at once.

This is a pretty half-arsed garden shed method and would never get used in any sort of production, but suits the one off approach.
Contrary to what others state, a large chunk of money was saved by doing this, that then went to pay for other parts of the build.

Paul f32#81

teamvmg.weebly.com

The savings are highly dependent on the cost of your own working (and thinking) time.

Time which you dont sum up and multiply with $$ anyway when doing something worthwhile. I work to live, not the other way around.

Has anyone tried resin infusion with this method? As long as you can find a way to stop the joins in the mould becoming race tracks it should provide a good product with the advantage of giving you unlimited time to get everything set up perfect.

No mould involved, just a pipe. infusion would work well, just that it would help if the carbon fiber is a bit tacky somehow to hold in place when positioned.

The pipe is the mould. With what I understand of your current system, when you set the up the infusion you would probably end up with resin running up the join in the pipe instead of through the fibres. This would result in a lot of dry areas. Having said that it would be relatively easy to set up your bag so the resin would go in one gap, through the fibres and then out the other gab. I might do an experiment at some stage.

There are spray adhesives that are used to hold fibres in location while setting up.

Whats your recommendation on the spray adhesive? I'm just about to do a small tube
regards

Thanks for all of input! I’ve been off line the last few days working on the boat burning midnight oil.

I received the woven braided tubing very interesting material. I have not made a final decision on the molding method yet. The braided tube will give me a continuous weave that will expand or contract and keep the fibers in the correct orientation.

Any way that is the fun part about boat building is figuring thing out and coming up with ingenious ways to solve the problems.

Go out and buy it pre-made has never been cheaper! Plus that spoils the fun.

I’ll let you know how my method works, and it is a precursor for building the beams, which will be a unique shape. I had the engineering performed on the beam shape and it proves out structurally stiffer then a circle or teardrop.

I've never found setup time much of a problem.I only lay a thin layer of resin over each layer of uni carbon with a squeegee and rely on the pressure to push the resin through the fibres for saturation. Drop it in the mould, fold the layers over the bag put the top on and inflate.
Super slow hardener or a simple oven and pre-preg would be a nice way of providing setup time on big jobs.

What keeps the fibers in line? I found that uni wrapped in a cylinder shape want to stretch and not keep the fibers in proper orientation. I’ve also seen a problem with wrinkles I suppose enough pressure will resolve that issue but that tends to mess with fiber orientation also. Carbon is all about the proper fiber orientation.

I lay the uni in the orientation that I need over a light layer of plain weave glass cloth. It could be plain weave carbon but when Uni carbon is way cheaper than plain weave carbon the uni carbon and glass combo gives best value, given the plain weave is mainly for handling.

Because I only lay the resin with a light touch to the squeegee on to of the surface of the uni it does not move around. All laid up on flat surface and then it moves together because of the plain weave. I've had no issue with fibre orientation.

Good idea.

It's just a PIPE there is no JOIN!

It is a pipe inside a pipe with two membranes. One with vacuum and one you inflate later on to increase pressure. I guess Scarecrow is still hung up on the split pipe method described earlier

Now, how would the ends of the pipe look, or is there a membrane able to hold 2-4 bar?

Sorry, hadn't payed enough attention, I now see you're cutting the pipe after making the part.

I like the idea of marrying several of these concepts. Use a split pipe and low pressure to form a thin carbon sleeve inside the pipe. Once cured, laminate and inflate again from inside the carbon sleeve you made in the split pipe and let it bond to the carbon sleeve (it becomes the outer part of the tube).