Thursday, September 27, 2007

Mast Assembly Details

I just completed the assembly of the mast this afternoon when I glued on the final side wall to close up the hollow box. I counted a total of 43 separate pieces of wood in the mast assembly, counting the scarf sections for the long pieces. It's definately not the work of a weekend or couple of evenings, but it went reasonably fast and everything went together smoothly. The photos below show a few of the details and the assembly sequence and methods I used.

The mast head has a built-in crane for the main halyards and internal wooden sheaves for the jib halyards, separated by a central divider. I built this assembly as a separate unit, so I could insure that all the exposed areas around the sheaves were well-coated with epoxy. In addition, the bearing surfaces of the sheaves, which are made of mahogany, are glassed over and then coated with an epoxy and graphite compound for a smooth, durable surface. You can see the black graphite epoxy coating in the photo below:

The masthead also has solid blocking around the crane area. To get a wiring conduit through this area I built the blocking with a channel just wide enough for it to pass through in the center. The conduit is flexible plastic irrigation pipe, with an I.D. of 1/2 inch. One of these in each mast half should give me enough space for a VHF coax, 12-volt circuits for a masthead tri-color and anchor light, and a cable for a Sea Me active radar reflector.

At the foot of the mast the conduit exits the side walls just above the solid wood packing above the mast heel. This wood packing at the foot is to allow for long screws to mount halyard clutches and blocks. I routed the wiring out the side walls since the aft side of the mast is occupied with the clutches and the forward side is taken up by the mainsail downhaul.

To keep the conduit out of the way during the final assembly, I epoxied in these tiny slats of 6mm ply. These weigh next to nothing and were simple to make. I ripped a couple of strips of the ply to the right width with 45 degree angles on both sides, then chopped them up into 3/8" wide pieces. They fit perfectly, the ends dipped in epoxy and simply laid in place to dry.

The slats also make it easy to pack aluminum foil into the mast halves by tucking it under them so it too does not move when the pieces are put together for lamination. The foil inside is supposed to be a passive radar reflector. I don't know how effective it will be, but it can't hurt anything and it was certainly cheap.

Here is the final assembly. I now have a straight, hollow box section mast. When the epoxy cures it will be ready to cut down to eight sides, then sixteen, and finally round. But that will be a job for next week.

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