Tuesday, June 16, 2009

A nose cone for a PVC pipe ama

Two years ago when I built my first PVC pipe ama in Fiji, I made the nose fairing out of a solid piece of fence post. I shaped it with a cane knife and a block plane. It performed well enough and didn't leak, but I didn't like the weight of it out on the tip of the ama.
This time I have prefabricated a foam and fiberglass nose cone that I will carry in my luggage.

The nose cone is built in the same way as a complete foam and fiberglass ama with a central plywood web and foam blocks glued to both sides with polyurethane glue. You can use either ESP beaded white foam or the blue or pink Styrofoam sold for insulation.

I did the rough shaping with a handsaw and electric hand plane. The final shaping is done with a sanding block.

About four inches of the cone is recessed to fit inside of the PVC pipe. Both the recessed area and the rest of the cone is shaped down to allow for the thickness of the fiberglass and fairing compound. I allowed about 1/8" or less for this.

Here the foam is fitted inside of a short section of 6" PVC drain pipe to check the fit.

The 9 oz cloth fiberglass is applied (with epoxy resin only!) from two sides allowing a double thickness overlap along the top and bottom. I used small round patches of fiberglass on the very tip where it is difficult to get the fiberglass to stay tight against the foam.

After the epoxy has cured, I applied fairing compound with a putty knife.

After final sanding of the fairing compound, the nose cone is ready for installation into the end of the PVC pipe. It will be held in place with a flexible adhesive sealant like Sikaflex or 3M 5200. Silicone will work if you cannot get the polyurethane sealant.
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