Oaracle Gets a Carbon Fiber Mast
By Gary Blankenship & Helen Snell - Tallahassee, Florida - USA

When Helen and I were building Oaracle, our Jim Michalak designed Frolic2 in late 2003 and early 2004, we discussed getting a carbon fiber mast to save weight and make it easier to raise and strike that spar. But when we priced one, we got sticker shock – it would cost as much as the plywood, fiberglass, and epoxy for the hull of our 20-foot boat. Or about $900 for the 17-foot mast.

We put that idea away and lived with the wooden mast, which cost less than a tenth as much to build.

But the idea continued to nag, helped by references here and there. I read about Gary Lepak using old windsurfer masts for his boats, putting one inside the other when he needed more strength and rigidity. The problem with that is those of sufficient length for Oaracle seem to be two-piece, which means there’s no way to stick one inside the other.

Bateau.com sells a kit for making carbon fiber spars and they had one that would fit Oaracle, but it was for a stayed spar and Oaracle’s plans are for an unstayed mast to go with its balanced lug sail. I tried, but couldn’t get the information on what it would take to beef the mast up for our needs. But from that site I learned about carbon and fiberglass sleeving; flexible, tubular fabrics that could be laminated over a core to produce a composite mast. But the basic materials didn’t seem to be available except in kits.

The final piece was discovering the website of Soller Composites, www.sollercomposites.com. Available from this source are fabric sleeves in different diameters and different materials – fiberglass, carbon fiber, kevlar, and combinations of the three. Owner Jon Soller also proved helpful when I had e-mail questions and is sympathetic and understanding of the needs of the backyard boat tinkerer.

The final nudge was reading one of Jim Michalak’s essays. Oaracle is built to his Frolic2 plans. As designed its mast is built from Douglas fir, square in section, and 3 inches thick at the base and partners, tapering to about and inch and a half at the mast head. Michalak wrote somewhere (I can’t put my finger on it at the moment) that as designed the mast might be stiffer than necessary. That means when on the wind and a gust hits the boat, the force is translated either into forward speed – or increased heeling. With two people, Oaracle is very stable, even in breezy conditions as long as you’re smart enough to reef down. Michalak has published stability tables and the Frolic2 design is impressive with two crew. With only one, it’s a bit more iffy, and I do a fair amount of single handing on Oaracle. A more flexible mast adds a safety margin in higher winds.

Now all I had to do was find a suitable, discarded windsurfer mast that could be beefed up with sleeving. That proved difficult. I checked a local windsurfing club and one about 150 miles away in Jacksonville, but either got no replies to my e-mails or assurances there were no old masts lying around. Finally I lucked into a business in Panama City that was reducing its stock of rental windsurfers and gear. I managed to get a two-piece 18-foot mast that was broken just above the joint, a 15 foot carbon/fiberglass one piece mast and a used sail; the latter two acquired in case they prove useful on some future project. Total cost: $70 of which $10 was for the 18-foot mast. Biaxial carbon sleeving and fiberglass sleeving was ordered from Soller Composites and Evan Reynolds, a friend who was interested in carbon fiber (in his case as a way to make lightweight motorcycle parts) volunteered to help.

click to enlargeThis is a piece of 2-inch fiberglass sleeving; the biaxial carbon looks like this but its black. The carbon biaxial I used was 7.5 ounce/square yard, and is also available in heavier weaves. The fiberglass sleeve is 10 ounce cloth. The unidirectional sleeving I got is 15.5 ounces/square yard (if I read the chart right) and if anything felt even heavier, perhaps as all the fibers were running in one direction. As the picture suggests, the sleeving expands and contracts to cover a wide range of diameters. The 2-inch carbon biaxial sleeving, for example, will expand to cover up to about 2.25-inch tube, and stretch out to cover on down to about .75 inches. (A good thing, since my mast tapers to about an inch at the top.) The 2-inch unidirectional is a bit more limited, fitting tube from 2.5 inches to 1 inch in diameter. (Source: Soller Composites).

First, a cautionary tale about epoxy and carbon fiber. I typically use an inexpensive, thick 1:1 epoxy for my boat projects. It’s great for gluing and laminates fiberglass well when applied with a plastic spreader. If I’m only coating the wood, I thin the epoxy, usually with acetone because otherwise it puts on a much thicker than necessary layer, and really uses up the epoxy. About the only draw back is if applied on a vertical surface, say filling the weave of fiberglass cloth, its thickness causes it to run, adding a lot of work to the finish.

I initially used this epoxy and three layers of biaxial sleeving of staggered lengths to repair the break in the two-piece carbon fiber mast, which had been cut down to 17 feet.. But after several days of curing, the carbon was flexible. The mast parts could move under the patch and it was easy to feel the ends of the break moving inside. It was sanded off so the patch could be redone.

Lesson learned: Use thin epoxies with carbon fiber (Jon Soller recommends WEST). In the course of this mast project, I used standard WEST epoxy, MAS 2:1 epoxy, and the economy 2:1 epoxy sold by Duckworks. All are thin epoxies (noticeably much thinner than the original stuff I used) and all worked well with the carbon fiber.

Back to repairing the mast. I decided to take a different approach to repairing the break. Following a request to buy a sample of a “regular” carbon fabric, Jon Soller sold us a square yard scrap of carbon that had the look and weight of heavy regular fiberglass woven roving, but with a much stiffer feel – if you bend it, it almost snaps back to flat. A piece was cut out to cover and generously overlap the break. Even wet out, this heavy carbon fiber was too stiff to stay stuck to the mast, so it was wrapped first in plastic and then with clear packing tape – sort of a poor man’s vacuum bagging. When the epoxy (WEST in this case) cured, there was no question the mast was fixed. There was no noticeable bend in the repair. Two more staggered layers of the biaxial sleeving were added over the repair, to spread the load and avoid hard spots where the heavy carbon layer ended. (The repair gave the mast a slight python-that-swallowed-the-pig look just above the midsection, if you look closely.) The repairs also overlapped the joint of the mast, turning it from two-piece into a one-piece, which I preferred anyway.

The repairs were sanded smooth and the next step was fairly straightforward. The entire mast was covered with two layers of biaxial sleeving, added one at a time, and allowed to cure between layers. A extra layer was added to the top half of the mast for extra stiffness there, and also at the partners.

A note about applying epoxy to the sleeving. The best way is to brush some epoxy on the carbon fiber and then use a gloved hand as a squeegee to work the epoxy in and spread it. It’s much harder to tell when carbon is saturated than fiberglass. The glass will turn clear when its properly wet out; the carbon stays black. I found that if the carbon looked a bit dry, it probably needed some more epoxy. Keep using your hands to squeegee the resin to get an even wet out without excess epoxy. And wear vinyl or rubber gloves, latex will tear or wear through, even on smooth fabric.

Also, make sure to sand the spar smooth between layers to eliminate any snags or fine fibers that stick up. (Wear a good dusk mask, carbon fiber dust is very unhealthy.) If there’s any thing to catch the next layer of sleeving, it will be all but impossible to feed the sleeving on the mast and certainly impossible to avoid snags in the fabric.

At this point, the mast seemed plenty strong enough, but still pretty bendy. The overall weight was probably doubled or better, but it was still a fraction of the wooden mast. An inquiry on the Duckworks online discussion forum produced advice that strands of carbon fiber tow (ribbons about 1/4-inch wide) could be run the length of the mast for improved stiffness. The tow was available cheaply on eBay, so I gave that a try, but a dozen or so strands, run the length of the mast didn’t produce any appreciable increase in stiffness. However, the mast was no longer perfectly round. I decided to add the final cover layer of fiberglass sleeving and give it a test.

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The lower part of the mast with the epoxy-cast foot and partners spacers to fit what was originally built into the boat for the wooden mast. The black stripes are the carbon tow that was added to improve stiffness – a wasted effort from what I could tell.

First with Oaracle’s bow on the beach, the halyard (led to the masthead) was used to pull the boat over to its beam ends. The rationale was if the mast was strong enough to pull the boat over, it wouldn’t break under a full press of sail in a knockdown breeze. It passed with no problems.

Next was a sail test on a one-reef, breezy day. The mast was noticeably more bendy than its wooden counterpart (not surprising since test on land showed it was much more flexible). It seemed to perform well, except hard on the wind on the good tack (when the balanced lug is leeward of the mast) when the sail seemed to stall. It may have been the bend in the mast was just enough to change the sail shape. On the bad tack (the sail against the mast) that didn’t seem to be a problem, but my impression was the mast bent less on that tack. Another sail on a moderate wind day (no reef needed) seemed to produce good all around performance. It seemed like I had a good mast for light to moderate winds, but one I didn’t feel comfortable with for stronger breezes.

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The interim mast, before the unidirectional sleeving was applied, in a fresh breeze. The bend of the mast is evident. This also shows the bend in the boom that the downhaul imposes, a took for controlling sail shape on a balanced lug.

I put the mast aside to ponder for a while, in the meantime taking the safe and certain wooden mast for the 2007 WaterTribe Everglades Challenge. About that time, I noted that Soller Composites had begun selling a sleeving of unidirectional carbon fiber, and in the right diameter for the composite mast. It looked a great deal heavier than the biaxial sleeving and Jon Soller confirmed that it was both heavier and should add quite a bit of stiffness to the mast. It was also considerably more expensive. After some more cogitation, and some advice from Helen (“do it!”), I ordered the unidirectional sleeving, and some more fiberglass sleeving. Since breathing carbon fiber dust when sanding is hazardous, I preferred to finish the mast with a layer of fiberglass so I wouldn’t have to worry so much (yes, I was wearing a dust mask) when sanding the mast to fair it and prep it for painting.

When the unidirectional sleeving arrived, I was impressed. The strands were much heavier than the carbon tow I had tried, more like the strands in heavy fiberglass woven roving. In fact, they were close to the size of the strands in the fabric I had used to repair the break in the mast. The strands were held in alignment by stretchy threads of spandex.

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Closeup of the unidirectional sleeving on the mast. It was butted up against the foot and partner block to try to avoid any hard spot there.

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The mast was sanded to remove any snags and unfairness – but it still took quite a bit of work to feed the unidirectional sleeving on the no-longer-perfectly-round mast. It took noticeably more epoxy to wet out than the biaxial sleeving, but when it was all done and set, the mast had achieved significantly increased stiffness. Still not as rigid as the wooden mast, but much better than it had been. I think it’s about what I aimed for – more flexible in gusts to reduce the heeling forces, but stiff enough to keep a good sail shape in a fresh breeze. Equally important, I have no qualms about its strength. The final layer of fiberglass sleeving finished the laminating, and it was painted white to reduce the heat absorbed by black carbon fiber in the Florida summer sun.

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The carbon mast with the unidirectional sleeving added (but before the final fiberglass layer). On the left is the original wooden mast.

It’s a much heavier mast than when it started, possibly three to four times as much. But it’s still only about half the weight of the wooden mast – possibly a weight savings of 15 to 20 pounds (one of these days we’ll get a scale and I can stop guessing about these things). There are three immediate benefits. One, the overall boat is lighter by that much – not an insignificant consideration when the boat must be beach launched as in the Everglades Challenge and perhaps hauled off mud flats in Florida Bay. Secondly stepping or taking down the mast is an order of magnitude easier – a not inconsiderate improvement when doing it afloat in choppy water. The last advantage has to do with the mast shape. The beaded parrel specified by Michalak to hold the yard to the mast slides effortlessly up and down the round carbon mast. Sometimes it had the tendency to bind slightly on the square wooden mast and it was never as easy to hoist as on the carbon spar. That’s a comforting feeling on a dark night and rising wind with the prospect of reefing becoming more likely.

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The finished and painted carbon mast test fitted on Oaracle. The sailing trials will have to wait awhile.

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The yard parrel fits easily around the round mast and has less friction than the square-sectioned wood mast.

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A note about the mast step and partners. Those are sized for the wooden mast, which is three inches square on the lower section. The carbon mast started as a two-inch diameter round spar. Even with the multiple layers added, it’s probably only about 2 1/4-inches or less. The step and partners could have been reworked to fit the skinnier mast, but that would have precluded using the wooden mast again. I decided to “cast” a step and partners on the carbon mast to fit what was already on the boat. The step was lined with plastic, and the partners were thoroughly waxed and the bottom and open side sealed with tape. Then the step and partners were filled with thickened epoxy and scraps of fiberglass. The partners proved imperfectly sealed and leaked a bit; fortunately I had a drop cloth around the base to catch the mess. If I were doing it again, I’d make wooden blocks to fit the step and partners, and then use a hole saw to drill holes to match the mast’s rake (some folks might be able to free hand that; I’d need a drill press). Then the blocks could be glued to the mast at the proper locations.

With the benefit of this experience, if I were doing it again I’d change the layup schedule for this mast. After repairing the break (now I’d use the unidirectional and a couple layers of the biaxial sleeving), I’d start with the undirectional sleeving, and follow it with a layer of the biaxial. Then I’d test it and expect this would have almost the same stiffness as my finished mast. If satisfied, the final layer of fiberglass would go on. Probably this would come out about five pounds or more lighter than my finished mast. I think about a quart of epoxy or less would be enough for all three layers, possibly with some left over. My version probably used about a half gallon.

I got my broken spar for $10, and spent about $300 for materials to repair and strengthen it. That cost would be reduced to around $200 with the revised layup that I think is strong enough. That’s a third to a quarter of the price I was quoted in 2004 for a custom made carbon fiber mast, although I’m sure the custom mast would have been as stiff or stiffer and somewhat lighter as well. For me, that’s past the point of diminishing returns and not worth the extra cost.

But then again, even with scrounging for a used mast, the carbon spar cost three to four times what the original wooden one – built out of high grade Douglas fir – did. For me, it’s seems worth it as the boat will be easier to set up, and raising, reefing, and striking the sail will be easier.

As Oaracle and I respectively are both undergoing some routine maintenance and upgrades, it will be a while before I get to extensively wring out the new mast. I’ll try to provide a short update report then. But I’m confident the carbon spar will be the mast of choice from now on. I also think this has an application for other small boats. We used to have a 20-foot v-bottom catboat daysailer, designed by Phil Bolger. It’s perhaps the best handling and most fun to sail small boat I’ve ever had, but it was a major pain to set up. As originally designed, the solid wooden mast ( just over 18 feet long) had to be stood up vertically and then dropped through the deck partners and into the step (which of course, couldn’t be seen). It was both tricky and exhausting (to be fair, the boat was designed to be left in the water most of the time). It was eventually replaced with an aluminum tube mast (17 feet long), set in an above deck tabernacle, but it was still slightly dicey raising and lowering it and I once almost dropped it on Helen. A carbon fiber spar would have relieved most of the worst problem for using this boat. However, since it carried about 25 percent more sail than Oaracle, I would have beefed up the spar, probably using two instead of one layer of the unidirectional sleeving and maybe a second biaxial layer as well.

In the for-what-it’s-worth department, I suspect the original unmodified 18-foot spar carried a sail nearly as large as Oaracle’s 113-square foot lug. But the strains are different with a lug sail than with a windsurfer sail that has a highly curved luff. Obviously some strengthening was needed because the mast had already broken once. But I’d guess – and this is a guess as I’m not a carbon fiber expert – that most of what was added went for stiffness and there’s a great deal of redundant strength in this mast. For boats with smaller sails, using unmodified (and unbroken!) cast off windsurfer masts would probably work well. And several innovators have adapted windsurfer masts and sails to their home-built boats; I’m thinking about trying my used sail and extra mast on our Michalak Piccup pram..

It’s also possible to use a wooden spar as the core for carbon fiber. Graham Byrnes, on his winning design for the 2007 Everglades Challenge, needed lightweight unstayed masts that could be easily raised and lowered. He used aluminum for the lower sections of his masts (if memory serves) but the top several feet were wooden birdsmouth sections, and covered with carbon fiber to produce a combination of strength and light weight. They performed well for him.

If you’re looking for a light mast that’s no longer than a windsurfer spar and are willing to spend more than for a wooden mast (but not as much as for a factory-made spar), this is one alternative to consider.

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