XVI. Assembling the Masts

Building the Core Sound 20

While working on the four-day process of installing the deck panels, we also began assembling our masts. The masts are assembled from 3", 2.5", and 2" diameter aluminum tubing. To join the sections together, each of the smaller sections must be wrapped with fiberglass to create a set of bushings that will fit snugly inside the next larger mast section. This turned out to be a quick and relatively easy process.

First, we took measurements to establish how much thickness our fiberglass bushings needed to build up on each mast section. Then we cut a small block of wood to that thickness to use as a visual reference while wrapping each mast section with fiberglass tape.

Next, we roughed up the aluminum with 80-grit sandpaper wherever the bushings would be applied, and cleaned the surfaces thoroughly with acetone.

Then we cut 3" wide, 6 oz. fiberglass tape to approximately 6' lengths (longer lengths become difficult to wet out and work with), pre-saturated them with epoxy, and wrapped them onto the aluminum sections until adequate thickness was built up. We found it easiest to wrap with pre-saturated tape until the bushing was just slightly shy of the needed thickness, then we switched to dry tape for the final few wraps to absorb excess epoxy and prevent messy drips. While seating the dry tape, we took care to keep wrapping in the same direction, gently massaging it with our fingers. This resulted in the double-benefit of more quickly saturating the dry tape and tightening the bushing to prevent air bubbles or wrinkles.

About four hours later, when the bushings were almost entirely cured, we used a block plane to gently shave down each bushing to a perfect fit with the corresponding mast section. We thought it wise to err on the side of a snug fit so we could pound the sections securely together with a rubber mallet. Great care must be taken with the mallet to avoid denting the aluminum sections (which would compromise strength), but ours slid together very nicely.

Next, we applied more fiberglass tape to create a "shoulder" at each joint to prevent each mast section from sliding further down inside of the next larger diameter mast section. Once these cured, we sanded everything smooth to give it a nice, finished look.

Next, we roughed up the masts with 80-grit sandpaper, cleaned them with acetone, and applied the same Systems 3 primer and finish paint (Whidbey White) that we used on our boat's interior. This made the masts much more attractive and cooler to handle in the sunlight. The white paint deflects some of the sun's rays so the metal doesn't get quite so hot.

Up until this point, we deliberately left our masts long, but before proceeding, we laid out the sails along each mast, measured the luffs to calculate the necessary amount of sailtrack, and marked any excess. We decided to leave each mast about 6"-8" longer than the top of the sail to accommodate the halyard block and any stretch in the sail, but then we cut off any excess tubing at the top of each mast.

Next, we attached the sail track which the sails will slide up and down on. The sail track is attached using stainless rivets, 1/8" diameter x 3/8" long. Each rivet must be coated to isolate it from contact with the aluminum to prevent galvanic corrosion. We dabbed each rivet with 3M 5200 sealant before insertion

The sail track needs to be "faired" across each transition or "shoulder" where the tubing steps down in diameter. The plans recommend wood or fiberglass wedges for this purpose, but we squirted extra 3M 5200 sealant into these gaps and skipped 3 rivets at each transition. Later, when the 5200 cured firmly enough to support the track, we inserted rivets into the skipped holes. The 5200 will weather well and is less labor-intensive than making wedges. Just be sure to keep the track edges clean, as residual 5200 may prevent smooth sliding of the sails.

Next, we attached the other rigging hardware (eye straps, cleats, etc.) to the masts, which was a big job. Although it is acceptable to thread bolts directly into the aluminum by drilling and tapping each hole, it is best to use fine-thread bolts for this purpose. The only 316-SS bolts we had on hand were coarse-thread, and a quick test on a scrap piece of tubing confirmed that we could yank the bolts out of the thin-walled tubing a little too easily for our liking. Since we don't want our masts coming apart underway, we decided to through-bolt each piece of hardware, which entailed fishing the nylock nuts up through the inside of the tubing.

To accomplish this tedious feat, we taped a wrench to a 7' long stick and taped a nut in the mouth of the wrench. Anna stood at one end with the stick while Wes sighted down through each bolt hole to line up and screw into each nut. It took about six hours to attach five pieces of hardware this way, but the effort was worth it, as our hardware is now firmly attached. If you choose to do it this way, be sure to work from the middle of the mast out towards the ends. Otherwise, hardware attached near the ends will get in the way as you try to attach hardware nearer to the middle of each mast. Here, too, we again pre-coated and bedded each fastener with 5200 prior to attachment in order to prevent galvanic corrosion.

Once the masts were cured, we installed them in the boat and hoisted the sails to check the fit and arrangent of the hardware. Everything fit well, so next we're on to attaching the deck hardware.

UPDATE (July 2012):
After four years of sailing, we decided to lengthen our masts to increase the clearance under each sail. Our sails were cut slightly oversized, so they extended so low that we needed to duck in order to tack and to see boat traffic on the lee side when heeled.

We added 12" to the main and 14" to the mizzen, resulting in a 22'3" main mast and a 21'3" mizzen. The extensions were made from the same 2" diameter 6061-T6 aluminum tubing used for the top sections of the original masts. We milled a 6" long aluminum spline (1/8" wall thickness) to fit exactly inside the 2" tubing, then pop-riveted in place.

With the sails fully raised, there is now 20.5" clearance under the tack of the main sail (above deck), and 36" clearance under the tack of the mizzen sail (above thwart). This has made a wonderful improvement to our visibility and comfort aboard.

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