BUILDING A CARBON FIBER DINGHY MAST
Experiment on laying up a Carbon Fiber mast
Since my Birdsmouth mast works perfectly well it's obvious I need to make a new one Just for Fun!
Researching Low Tech Carbon Fiber Construction.
There is not a lot of information for the un-initiated on using composite materials such as fiberglass and Carbon Fiber to make small low tech masts.
Some information is available from Bike builders who like to use carbon fiber frames. Some of the procedures translates to boats but not enough. Performance Car also use lots of Carbon fiber but again it's not all that useful for mastmaking.
In desperation I turned to the Boat Design Forum. Although I was very obviously a beginner with little knowledge and less experience, a few people were kind and shared information with me. Among them Eric Sponberg, Naval Architect, Sponberg Yacht Design Inc., St. Augustine, Florida was kind enough to give me some guidelines. Basically he suggested I look at aluminium masts and build something with similar proportions. HE DOES NOT ENDORSE MY COMMENTS OR BUILDING METHODS IN ANY WAY. He was simply generous enough to share some much appreciated pointers.
Often when building a carbon fiber mast, or even fiberglass, an inside tapered mandrel is used and the carbon fiber cloth is wound on the outside. When the resin has set the mandrel is removed using strong machines. Often the mast is vacuum bagged and in many cases the Carbon fibre/resin is the pre impregnated kind that needs high temperature to cure.
Although I have a vacuum pump I don't have any of the fittings and certainly don't have a curing oven, let alone a steel tapered mandrel with the machinery to extract it from the finished mast.
Good beginnings I would say! I don't know what I'm doing and I don't have the tools anyway!!!
One thing I do have is a clear view of what I would like to end up with. I want a longer mast than I have now, lighter and strong enough to allow me to experiment with several different rigs without damaging the balance of my boat by having a very tall heavy mast. My current mast is 12 feet long. Another requirement is that the new experimental carbon fiber should look OK. I understand that an experimental mast will be imperfect.
My plan to build a Carbon Fiber Dinghy Mast
Being eternally optimistic and confident in my ability to improvise
I made a plan! The plan was simple if time consuming:
- I would make 2 identical 6 feet long moulds made of a halved water pipe, and join the various sections to produce an inner core. I would end up with a straight, light, hopefully stiff enough inner core on which to wind my various other layers.
- I had used slow cure epoxy in building my Skerry and appreciated the long work time. Also the MAS epoxy I used did not blush.
- The pressure required for the various layers that would go on this inner core would be provided with packing shrink wrap. I hoped that the slow cure time would allow me the time to gradually and carefully bind my mast while keeping it straight. Success was based on my skill on keeping the mast assembly from sagging and distorting and on my ability to wrap the layers neatly in plastic wrap.
- I hoped to keep adding layers before the previous one had had a chance to set completely improving the cohesion of the laminations and avoiding delamination. Ideally recoating within 12 hours allow the different epoxy layers to bond together.
- Even more hopeful I intended to check the strength and flexibility as I went along and stop when I had enough. My preliminary plan was to put 3 layers of carbon fibre on top of the fiberglass inner core, plus some reinforcement where I hoped to attach fittings. If any area required stiffening I would add a tapered layer. I planned to wind 2 diagonal layers and one longitudinal layer.
- The top foot of the mast has either a hole or a block to allow for the halyard. This I planned to sculpt in blue foam and cover with glass/carbon fibre. This will be quite easy since I have a lot of experience sculpting foam from my previous experience as a model maker/Industrial Designer.
- Finally I planned to make small holes along the hollow mast and use construction spray foam to allow the mast to float if I went over. This foam might provide rigidity but that was not a requirement, just a side benefit if it happened.
Making a mold to cast the inner core of my Carbon fiber mast.
The mould is made of a 3/4 inch thick medium density particle board. It is nice a stiff and is not likely to warp. The pipe is just a regular water pipe. It is about the size I hope to finish at.
I assembled the box gluing and screwing the wood (I later removed the screws because they were too long and I was afraid to damage my table saw blade). The pipe is glued in using PL adhesive. It is important to fit the box quite closely to the pipe.
I was extra careful to keep things straight and accurate. I'll have lots of chances to warp things later!!
I chose to make a smaller mould because I had shorter material on hand AND it is easier to control and be accurate with shorter sections.
Box and pipe are glued, screwed and clamped.
The wood is glued and temporarily screwed, then clamped.
The pipe was slightly longer than 6 feet but I did not shorten it. Some of the wood was shorter but it did not seem to matter. Just not as tidy. I used a 4 feet by 2 feet medium density particle board. It weights a ton but seems quite reliable and unlikely to sag for this application. I had to make joins to get 6 feet but I staggered the joints and it didn't matter.
Assembly has been carefully cut down the middle then glued together side by side.
After allowing the assembly to dry it was split down the exact middle of the pipe. I did this in 2 passes of the table saw, turning the mould over but making sure that the same side of the box faced the fence in both cuts in case I had been inaccurate in measuring.
The 2 halves were then glued side by side. I did this to make an already stiff mould stiffer and to simplify handling.
The first cut burned the wood so I raised the saw blade. This helped the second cut.
My blade is a narrow kerf and the material removed is not quite an eight of an inch. I don't think this will matter much because when I assemble the 2 halves there will be some glue thickness that will restore some of this pipe back to round.
I cut long thin strips of hardboard to create a lip. These were screwed against the top of the pipe mould. I was careful to leave enough space to easily access the inside of the mould.
Everything is coated in packing tape and waxed.
I cut long strips of fiberglass that overlapped and laminated these in the mould. Lots of little threads are very annoying but I suppose harmless. I only laid one side up to run a test.
First fiberglass layer done on the right side. I used 2 strips and overlapped them in the middle. One layer only at the top. Hope this is stiff enough.
First layer of fiberglass has set and I've detached the moulding but left it in the mould. It was simple to take out and did not stick at all. Some resin had crept inside the lip and made a slight flash. It is very thin and I think it will be easy to just cut off with scissors.
In the detailed photo it is easy to see the overlap of the 2 fiberglass strips I used. Where there are 2 layers the moulding is more opaque.
So far all the materials have been left overs from my Skerry build. The epoxy is over 2 years old and the resin had a crystallized layer at the bottom of the bottle. The hardener was unchanged. The cloth was from cut offs from the glassing of the Skerry bottom and interior. So far the only cost is the water pipe, under 10 dollars. (I had the adhesive, and the particle board. I just had to clean it up.) That will change when I buy more resin/hardener and carbon fiber cloth.
I have lifted out the moulding and it is a great success. It is quite rigid but has some twist. I am not concerned about that because the 2 pieces glued together will eliminate this. The flash is clearly visible. It is very thin and it will be easy to just cut it off once the halves are assembled. The flash will help align the 2 pieces so is an unplanned benefit! One point for the good guys!
First piece of inner support for carbon fiber mast shows flash that crept under hardboard lip.
First half tube section of 6 feet is quite stiff.I am holding this fiberglass half tube on only one side. It is very light and stiff. There is about a quarter inch deflection only. This is much better than I expected. The outside surface is extremely shiny (can't see this because it refuses to show up in photos) and will need to be roughed up if other layers are to stick to it. I have never had any trouble with epoxy not sticking to itself yet so I'm not worried.
I went shopping today. I had used up the last of my epoxy resin so needed more. I also wanted to snag some carbon fiber cloth if I could. I had hoped to find tube material but the only source I could locate was far away and I would have needed to mortgage the cats to be able to afford it.
The goddess was on my side and Noah's had a mixed carbon / Kevlar cloth at pretty much half price. 30 dollars Canadian is not cheap but it's feasible. I'm not sure how much I will use because I plan to keep adding layers until it is stiff and strong enough. I expect I will have lots left over, but I wanted the full length of the mast--almost 19 feet, without any breaks.
7 yards of 40 inch wide carbon fiber and Kevlar cloth. Note: I only used about a third of the material I bought. The rest of the carbon fiber kevlar went into fixing the floor of my Tanzer cockpit and lots of other little projects. It was nice to have it around.
Laid up 2 more sections 6 feet long. I'm planning to lay up 2 sections every day and have them ready to assemble next week. (it's the boat show this week end so not too much work is likely to happen.) I need 6 half sections of 6 feet plus whatever I am doing to the top.
I dropped in the Dollar store and picked up a couple of rolls of shrink wrapping plastic, some cheap paint brushes and some plastic cups to mix the resin in. I had some gloves and popsicle sticks left over from the boat build.it's really amazing how expensive the "little" things can be. They really add up. it's easy to faint at the price of the cloth but if you add up the gloves, paint brushes, dispenser pumps, plastic wrap and tape, wax paper, respirator filters, popsible sticks and sandpaper, to mention a few, then the cost can sneak up quite a lot.
Finally got the 6 half sections moulded and ready for assembly. I placed 2 pieces in mould and clamped them securely in place butted against each other. The mould kept them nicely lined up and gave me an easy way of clamping the pieces straight and even. Then used little pieces of fiberglass to glue the sections together.
I found after the first join that adding thickened epoxy first to bridge any gap worked best. I supported the long ends sticking out.
Joining sections together using the mold to hold sections in position.
My assistant is dubious about the project.
I laid the long half sections side by side on the plastic sheet and prepared the mixing pots, resin, gloves, thickener, tape and pushed off the assistants. There is some curve in the sections but that will cancel out as I assemble them. I am planning to use the floor boards as marks to keep the assembly straight.
First I aligned the 2 sections and taped them together with masking tape, at roughly 2 feet interval. This eliminated any distortion and curl in the sections and gave me a nice long cylinder. I then made a solid strong tape joint on one of the sides. This would act as a hinge and make sure the 2 pieces would stay together properly aligned. After removing the tape on the other side I carefully opened the hinged sections. Using a plastic bag with a hole in the corner I squeezed thickened epoxy first on the back hinged joint, then on the 2 open edges. I closed the edges and taped them again at about 2 feet interval.
After checking that everything was lined up and there were no obvious problems, I ran my gloved finger along the joint and used paper towels to remove any extra glue.
Taping the edge kept everything solidly together while I wrapped the whole thing in a couple layers of shrink wrap. I'm not sure it is necessary but I'm hoping it will help keep a move even pressure on the mast core. As I wrapped it it did get rounder and smoother so I guess it worked. I taped the mast core on the floor along one of the floorboards to prevent cats from knocking the assembly out of line.
I tightened the plastic wrap too tight and the 2 fiberglass half tube sections did not stay aligned. When I unwrapped the tube the 2 sections had hardened in the wrong position. It made an uneven oval rather than a round profile. The good news is that is was very solid and rigid. Holding it by the middle, the 16 foot tube only bent about 4 inches. So GOOD NEWS/BAD NEWS.
I had to decide if I could fix it. I think it is possible to use this eventually ending up with a strong mast but not an even one.
My first impulse is to salvage what I had. After a while I realized that I would apologize to everyone and myself if I was not happy with the mast. So I started again making half tubes. I have re cast 2 pieces. This time though I have made it more substantial. Since the not so good tube is actually quite substantial and strong I have realized that the inner core IS structural and will add to the strength more than I expected.
I will keep the not so good tube and maybe use it to make an experimental sprit, or one of the spars for a balanced lug. I could live with a bumpy one of those IF I had a good mast. "Vanity thy name is Woman!"
I have now recast my fiberglass half sections, not so much work because I changed the procedure.
Before, I had hardboard pieces on top so that the fiberglass would stay within the mould and be finished size, this did not work because of flash squeezing under hardboard, and the difficulty of getting the woven cut fuzzy edge to line up properly. Now I removed the strips of hardboard and cast oversize THEN trimmed while not completely hardened.
This worked much better and is faster. I used 2 layers on one set but after, I added some extra pieces to stiffen sections. The new method produced better smoother edges that will join together better.
I end up cutting the plastic tape when I trim but it is very easy to retape so it is not a problem.
Between each moulding I wax the mould. I don't think this is strictly necessary but I'm not wanting to risk sticking.
I trim the extra fiberglass off after the resin has set but is not absolutely hard. I use a utility knife (another thing from the dollar store) and change the blade often.
How I did the first time
How I did the Second time. I used red tape instead of transparent because I had it around, no other reason.
Trimming the extra on edges. I have to retape each time but that's very quick.
Putting the new fiberglass core together with tooth picks to separate the halves about the same distance the saw blade took off the mould. Everything is taped together then I cut a whole lot of 1 inch or so pieces of fiberglass and used these to glue the 2 sections together. Every 6 inches or so. I wrapped each joint in plastic wrap (not too tight this time) and the result is quite good. Quite smooth, not perfect though.
After a quick sand of the core to make sure there was some bite for the new layer, and to get rid sharp edges, I set the core up on sawhorses, leveled it and got my stuff ready.
End view of the inner fiberglass core.
Cut 2 long thin strips of carbon fiber and rolled them up.
In order to avoid the fuzzy threads of Kevlar/Carbon fiber I used masking tape to protect the edges when I cut the strips. This was a lucky choice because after I soaked the cloth in resin, the tape just came off. It worked very well. Lucky break.
I had lots of time to work because I'm using slow set MAS epoxy. This removes some pressure
I had set up a board just beside the core and moved it along as I worked. It is covered in plastic. I set out a length of cloth, brushed resin on the back and made sure it was well saturated but not drippy, then carefully rolled it onto the core removing the tape as I went. I had lots of gloves and only prepared a manageable length each time. I tightened the cloth as well as I could. There is a very slight overlap of each turn.
Every 3-4 feet I would wrap the section in shrink wrap after putting on new gloves.
I only prepared a small amount epoxy at a time, as I went along. I don't think I have a single drip of epoxy from the layup.
First layer is a diagonal layer. I work on only a short length at a time removing tape as I go. The tape softens and just comes off.
First layer applied and wrapped in plastic
This is a detail of the mast showing the first Carbon fibre/Kevlar layer wrapped in shrink wrap plastic. The edges of the long strips were fuzzy but the plastic wrap flattened them down nicely. The mast seems quite even. There are a couple of bulges but nothing outrageous. I am hoping that the next layers will smooth these out.
The shrink wrap tends to forms little folds when it is stretched and I have not been able to avoid these completely. Again I'm hoping that these will not matter too much.
Come morning I unwrapped the mast and checked it out. So far so good. The epoxy is still flexible so I think the next layer will stick well.
My mast is still 18 feet long. I will trim to final size when I'm finished laying up the mast.
I gave the mast a quick sand to remove any fluff or sharp edge. Nothing much came off. It is quite smooth but not perfectly even.
First Kevlar/Carbon Fibre layer hardened and plastic wrap removed. Tube is quite stiff. It is also straight. Before I went to bed last night I flashed the lazer pointer I use to play with the cats through the tube to make sure it was straight.
Draped the Carbon Fiber/Kevlar cloth on the mast and gradually wrapped it all the way around.
I cut a strip of cloth the length of the mast and twice the circumference plus some overlap. The edges are taped so not too much fuzzy threads to deal with. I only make up a small amount of resin at a time but had to work fast because the roll started heating up. If the resin starts setting before the cloth is in place I could be in trouble.
Wetting the cloth on a board this way allows for nice control of the amount of resin. Again no drips and no waste.
I carefully draped the carbon fiber/kevlar cloth on the mast starting at one end and worked to the end. This cooled the roll and prevented the resin from kicking off too fast.
I gradually smoothed the cloth onto the mast and stretched it as best I could. I think a second set of hands would have been useful in this step. Eventually I had the layout smooth and quite straight (mostly!)
I would have been easier to do only one layer, not the 2 that I did.
Starting at one end, I slowly wrapped the mast in plastic wrap. This step was surprisingly difficult because the 2 layers wanted to slide and I kept having to smooth little folds and bumps. I eventually wrapped it quite loosely to get everything in place and went back and wrapped more tightly. I was able to smooth out the bumps that had formed.
The assembly is now sitting nicely in the living room, checked that it is straight and hardening.
The whole bundle is wrapped in plastic and setting up. I expect this will take at least 24 hours. I don't intend to add another layer until I have tested the mast. I want it to be strong but slightly bendy. I don't have enough experience to know if the 2 layers of fiberglass plus 3 layers of carbon fiber Kevlar are enough. I have extra length that I can break if I need to.
The house is cool so set up will be slow. It is stormy and cold outside.
All wrapped up waiting to harden. At this point the mast weight is less than 8 pounds and this includes the plastic wrap and stuff hanging off the end that will be trimmed. I'm hoping the mast will be less than 10 pounds when finished.
After unwrapping the bundle I checked the mast. It is strong. I don't think I could break it. Well I could if I really tried and had a hammer, but under normal use it would stand up. It was quite bendy. Over 18 feet I could deflect it 6 or more inches. Very scientific this all is. Since one of the rigs I want to try is the triangular sprit, I need slightly less flex. I added another layer of straight cloth with some slight overlap. Tucked it in its double plastic wrap blanket and put it to bed till tomorrow. It was much easier working with only one layer not 2 thicknesses as the previous lamination had been.
One thing I was careful to do is not put quite as much resin as I had last time. Because I was working too fast yesterday, for fear the heat would build up too much and kick off the lamination, I did not brush out the resin as well as I could. This made the resin flow around the edge of the plastic wrap and made it difficult to remove. It took time to get the little imbedded threads of hardened resin out. I also had to sand some of the thin resin strands. Before I put this last layer on I brushed the mast with resin so it would flow in the little pits that were left once the edge of the shrink wrap were removed.
Now I must wait till it's warm enough to test under sail. Sigh...
So far What Have I figured out?
- It is possible to make a Carbon Fiber mast with low tech approach.
- There is a considerable weight advantage. My 18 feet carbon fiber mast weight slightly over 3.5 pounds with no fittings.
- Making the wall about as thick as an aluminium mast seems to work. Strength testing will have to wait till further live experiments have been carried out. For more information check out my page on the properties of carbon fiber.
- Casting small pieces and putting them together to create a core works and is manageable by one person. It permits control and is never difficult. It also facilitates making a straight tube.
- It is very hard to make a smooth tube.
- The tube / mast is strong, it might yet be too bendy but that can be fixed with another layer if required.
- If I had to do it again I would use a larger diameter pipe. I think I would gain more rigidity.
- There is not a huge gain over the other methods used on the web to create a core. (either using a pipe core with foam, or a pipe with melted wax) except that this method is simple and easily controlled. There is a link to the video of Cherub class dinghy members making a mast at my research page here. Link to some of my research. Videos etc.
- A tube (sock) of carbon fiber instead of wound layers would have produced a smoother mast. It would also have cost about double what I paid.
- It is not any harder to work with carbon fiber than it is to work with fiberglass at this skill level. Using slow set epoxy buys a lot of time and reduces stress.
- Shrink wrap works fine but it is hard to avoid pulling folds into the plastic. It is important not to put too much resin on the cloth otherwise when you wrap it the stuff oozes over the plastic wrap layers and makes it harder to remove.
MEANWHILE... I hoped to be able to shape the top of the mast to allow for a sheave to be inserted. I formed a pink foam block onto a cylinder and carved the opening. I use Static Guard to prevent the sawdust and small pieces from sticking to everything. The stuff can just be swept up after I use the spray.
After carving the foam I covered it in resin and fiberglass. It was quite tricky and the fiberglass did not fit very well in the sharp angles. I will have to figure out a way of glassing this.
NOTE: The foam did not work very well and I decided to make simpler wooden insert. see Puddle Duck Mast
MEANWHILE I started turning the pulley. I have a sheet of delrin and cut a blank using a hole saw. Mounted the blank on the drill press and used rasp and chisel to shape it.
This is experimental and might or might not work.
Rough cut sheaf is deliberately left too thick. I will modify once I have the top section finalized. I had a sheet of this plastic from one of my previous lives. It is very hard and slippery.
NOTE: In the end I decided against putting this in and opted for a simple wooden insert with a hole at the top. If I need a block I can tie one on as I do on the Skerry. I've decided to experiment with this mast on a Puddle Duck Racer I'm building for fun. I also plan to use the rig on my Skerry since the dimensions will work for it too. see Puddle Duck Mast
This web site reflects my personal ideas and doesn't represent anyone else's point of view. Although I was successful in making a carbon mast, it is not particularly smooth. If I was to do this again I would use carbon fiber socks rather than strips. I did not have enough money for them in this experiment. Bateau.com sells mast kits.