Custom Search
   boat plans
   gift certificates
Join Duckworks
Get free newsletter
on this site
by Gary and Helen Blankenship Tallahassee, Florida - USA

Several years ago, I managed to convert a broken 18-foot carbon fiber windsurfer mast into a functional mast for my 20-foot cabin beach cruiser which sports a 114-square foot balanced lug sail (Jim Michalak's Frolic2 design).

It's been a great success at less than half the weight of the original wooden mast and has withstood some severe conditions, carrying the boat to four Everglades Challenge finishes including in the infamous 2012 heavy weather event. But the execution was not as refined as I would have liked; there was too much experimentation and a variety of carbon fiber, from quarter inch wide strands (called "tow") to woven fabric (like fiberglass cloth) to unidirectional weaves, was used. The woven fabric sleeves added strength, but left the mast too bendy. The strands of tow probably added strength but I couldn't tell any difference and they left the mast looking imperfectly rounded.

The unidirectional sleeving finally did the trick, adding both stiffness and strength. But there was at least one extra layer of unneeded woven sleeving and two of fiberglass (whenever I thought the mast was finished, the last layer was always fiberglass sleeving). Given another chance, I thought I could do better.

That chance came. At the same time I got the broken 18-foot mast, I also bought a used, unbroken 15-foot windsurfer mast, although this one was a combination of fiberglass and carbon fiber. Nearing completion is a 19-foot sailing kayak (a Michalak Trilars design, stretched four feet). There will be a lot of playing around to determine the ideal rig. The initial one will be a 55-square-foot balanced lug from my Piccup pram - almost certainly too small (it requires about a 9-foot mast). The 15-foot mast should allow a lot of flexibility for different types of sails.

It does have the same problem as the longer Windsurfer mast, being designed for a sail that requires a very bendy mast where a much stiffer mast is needed for the sails I'll be using. (I ruled out using a Windsurfer sail because it's difficult to reef them and the mast will go through partners, which restricts the size of the Windsurfer sail.)

The mast had been sitting outside for several years, mostly in the shade, but getting a bit of sun now and then. The result was the outer layer had deteriorated, getting prickly. Grabbing it barehanded would result in microscopic splinters, like grabbing a handful of pink fiberglass insulation.

For the purposes of this project, that's even better. It's a good way to test the suitability of rehabbing such a mast, one that Duckworks' readers might be able to scrounge up for free or for a pittance.

OK, now a caution. Every time I buy carbon fiber, a warning is included about the dangers of sanding and breathing the dust. So when you sand, wear a good, airtight dusk mask/respirator and sand outside if possible.

That warning applies to preparing a mast such as this one. As was mentioned, it was prickly to the touch. There's no way to know for sure if those fibers are fiberglass or carbon fiber, so wear a dusk mask when preparing the mast. In this case, I washed the mast with rags soaked with rubbing alcohol to clean it and remove any mold or mildew from its long outdoor exposure. You could see fibers floating in the air.

The mast was next laid out with each end supported by a sawhorse. I pressed down with virtually all my weight (about 200 pounds), first to ensure the mast was still structurally sound and secondly to satisfy a curiosity on how flexible this spar actually is. Windsurfer masts tend to be quite bendable to fit their highly specialized sails. Even those strong enough to use with non-Windsurfer small boat sails (and most are) will likely be too flexible to be optimal. I wanted to have a (nonscientific) way to see how much stiffness was added.

With the prep done, the rest is fairly straightforward. I had some heavy duty carbon unidirectional sleeving purchased from Soller Composites ( that fit the two inch diameter mast and also would constrict to fit the taper at the top. The information on the Soller site gives the maximum and minimum diameters the sleeving can handle. The sleeving I ordered works on diameters from 1 to 2.75 inches. Feeding the sleeving on the mast is straightforward. Starting at the top, I pushed the sleeving on the mast as far as it would go, about a foot or so before it began bunching up. Now take the sleeving end on the mast and with a smoothing motion pull it further on the mast as far as it goes. Push more on and bunch it up, smooth it out. It's sort of like a slinky, carbon fiber snake is devouring the mast bit by bit. It only took a few minutes to work the sleeving on the mast. The only slight problem is some of the thin Spandex threads that hold the unidirectional strands in place will break and the strands will try to spread out. Also, you want to keep the strands fairly straight. Both problems are easy to address while "smoothing" the sleeving on the mast. When it's all covered, go over and make sure there aren't any humps or knots in the sleeving.

The bottom end of the carbon/fiberglass mast cleared up and ready for the sleeving of unidirectional carbon fiber.
The same part of the mast with the unidirectional sleeving. The sleeving was fed on from the top of the mast, so by the time it snaked the length of the mast, the Spandex threads that hold the strands in place were broken and stretched. While this looks a little rough, it’s actually easy to smooth the bumps and straighten the strands.
A particularly rough area where most of Spandex threads broke. But again, its not hard to straighten out the strands and it’s even easier to do that when applying the epoxy.
The top of the mast. Because the sleeving was installed form the top, this is straight and smooth.
The epoxy make it easy to smooth out the bumps and align the strands of carbon fiber. When the sleeving is saturated, it will have a shine. If it’s dull, it needs more epoxy.
Another section of the mast with the epoxy applied.
Adding the finish layer of fiberglass sleeving over the sanded unidirectional carbon fiber. The fiberglass sleeving, which is cloth instead of heavy unidirectional strands, is easier to install, epoxy, and sand.
The completed but as yet unpainted mast stepped in the lengthened Trilars main hull. It should allow considerable experimentation with different sails.

A short note. I wasn't sure how much sleeving to order since the mast ranged from 2 inches to about 1.25 inches and the sleeving could handle from 1 to 2.75 inches. Obviously, the sleeving would go further on a 1 inch diameter rod than one that is 2.75 inches. I ordered a couple extra feet, but as best I can tell, my mast used very close to 15 feet. You don't want to order too much extra as it costs $5.24 per foot (more per foot if you order less than 10 fees, less per foot if you order more than 30 feet).

Once the sleeving is on and straight, it's time to epoxy. Here you may have to do some research as not all epoxies are optimal for working with carbon fiber. My experience has been that thin epoxies work and thick epoxies may not let the carbon fiber harden sufficiently. I've had good luck with West and MAS epoxies. Proper application also takes a bit of practice. When using traditional fiberglass, the cloth disappears when it is sufficiently saturated. There's no such luck with black carbon fiber. It will get a dull look when soaking up epoxy, and then look shiny when it is saturated. Also, a regular squeegee or roller won't work on a round mast. You'll have to use your hands, protected by thick gloves. I wore two layers of the blue nytrile gloves sold at Harbor Freight and that worked well. I put wax paper on the sawhorses under the mast. The epoxy was brushed on and then I used my hands to squeegee it in and push the excess up the mast. Try not to do this on a hot day, or have a slow curing epoxy if you do. Take your time and make sure the carbon fiber is properly saturated, and work out any bumps, ridges, or sections where the sleeving may bunch up. When your finished go over the entire mast again to check for irregularities. Make sure the strands are relatively straight (perfection is not required) and even. Double check. A few extra minutes here can save a great deal of sanding later.

Once the epoxy has completely set, it's time to dust-mask up again and sand the mast. Hand sanding will be the most efficient because of the roundness of the mast. Wear thick gloves as stick-up strands of the carbon fiber can slice right though the sandpaper and into your hand. The little strands will be hard to see, so make sure you get them all. Otherwise at it will be impossible to slide the next layer of fiberglass sleeving on the mast, or if you manage, it will tear or fray the sleeving, leaving some blemishes on the final mast.

The fiberglass sleeving feeds on the same as the carbon fiber sleeving. Epoxying is even easier because you can see when the fiberglass is sufficiently saturated. I did the same as for the carbon layer, brush on epoxy and then spread and squeegee it with gloved hands. Depending on your taste for finishing the mast, you can paint it now or fill the weave with extra epoxy and then paint.

Remember when I test bent the mast with the top and bottom supported on sawhorses? I did it again after applying the unidirectional carbon fiber sleeving and was surprised that the mast was only a bit stiffer. The unidirectional carbon is rather thick and I expected a more pronounced change. However, after the final fiberglass layer, the mast was notably less bendy. Maybe the carbon had to be "sandwiched" and have an outer layer in order to maximize the stiffness.

I paid $50 for the original used mast, the carbon fiber sleeving cost about $80, the fiberglass sleeving about $15 or $20, and probably about $20 of epoxy was used (maybe a pint or so). That's several times what materials for a wood mast would cost, but a fraction of what a similar professionally made carbon spar would run. The carbon mast plainly won't have the appeal of a varnished wood, and I think it's a bit more bendy. It is, though, less than half the weight of a wood mast and actually easier to make - there's no cutting, tapering, laminating, and rounding of the wood. Both those are good reasons to consider upgrading an old windsurfer mast for your next small sailboat project.


Mike John came up with a great idea in getting this story ready for publication. He suggested if you have to feed the sleeving over the open end of the mast, such as the bottom end of my mast as shown in the first picture in this article, you might want to duck tape a tennis or hard rubber ball over the end to ease the feeding and prevent snags. I should have mentioned that one of the reasons I fed the sleeving over the top of my mast is it was covered with a hard, rounded plastic cap. That made slipping the sleeving over it easy. If you don't have that option, try Mike's idea.

To comment on Duckworks articles, please visit one of the following:

our Yahoo forum our Facebook page