Yard-spar...part 1
The yard is a spar that the top of the square sail gets attached to; together they are hoisted up the mast with a halyard when the sail is raised. When I sized the yard-spar, I intended that it be fabricated out of aluminum tubing:
https://docs.google.com/document/d/1W3XYiaP2WimTIslNXU_52wk01va0YgxlUhcxD0XA3LY#bookmark=id.7ujeuw3cel9g
A modern production sailboat has an aluminum mast, aluminum boom, aluminum spinnaker pole, so of course it’s going to be made of aluminum, right? Well, I happened to be reading one of Patrick O’Brian’s novels that is set in the Far East, and he describes the use of bamboo in the rigging of the local sailing vessels, so that got me wondering if it might work for my application. I did some investigating and found a company in Portland that sells Tre Gai bamboo, one of the strongest species that is commercially available for structural applications, so I ordered a seven foot section.
The upside of bamboo is that it’s strong, light, and renewable. The downside is that it is not an isotropic material and in this case the center of gravity of my pole differed from the linear center by about 3 inches:
One end also had a large crack which would degrade the strength in this highly stressed area.
My solution was to insert a dowel into each end of the yard-spar and cement it in place with some epoxy resin thickened with high density filler. Then I beveled the crack at a 45 degree angle using my Dremel tool, filled it with some of the same epoxy slurry and finally wrapped the ends with biaxial fiberglass cloth.
This not only strengthened each end of the yard-spar but it also balanced the spar and gave me a solid base that I can screw fasteners into as I begin attaching hardware. For anyone that does fiberglass work, you’ll see that the job isn’t pretty, but it is functional! The fabric was completely wetted with epoxy and I see no voids so I’m confident if the spar does fail, it won’t be at the ends.
I’ll use this bamboo yard-spar as a test case as I begin actually installing the blocks, cleats, braces, foreguys, etc. and see how closely the theoretical matches reality. It may be a keeper, but I’m still planning to fabricate a final version out of 3.5” OD 6061 aluminum tubing.
https://docs.google.com/document/d/1W3XYiaP2WimTIslNXU_52wk01va0YgxlUhcxD0XA3LY#bookmark=id.7ujeuw3cel9g
A modern production sailboat has an aluminum mast, aluminum boom, aluminum spinnaker pole, so of course it’s going to be made of aluminum, right? Well, I happened to be reading one of Patrick O’Brian’s novels that is set in the Far East, and he describes the use of bamboo in the rigging of the local sailing vessels, so that got me wondering if it might work for my application. I did some investigating and found a company in Portland that sells Tre Gai bamboo, one of the strongest species that is commercially available for structural applications, so I ordered a seven foot section.
The upside of bamboo is that it’s strong, light, and renewable. The downside is that it is not an isotropic material and in this case the center of gravity of my pole differed from the linear center by about 3 inches:
One end also had a large crack which would degrade the strength in this highly stressed area.
My solution was to insert a dowel into each end of the yard-spar and cement it in place with some epoxy resin thickened with high density filler. Then I beveled the crack at a 45 degree angle using my Dremel tool, filled it with some of the same epoxy slurry and finally wrapped the ends with biaxial fiberglass cloth.
This not only strengthened each end of the yard-spar but it also balanced the spar and gave me a solid base that I can screw fasteners into as I begin attaching hardware. For anyone that does fiberglass work, you’ll see that the job isn’t pretty, but it is functional! The fabric was completely wetted with epoxy and I see no voids so I’m confident if the spar does fail, it won’t be at the ends.
I’ll use this bamboo yard-spar as a test case as I begin actually installing the blocks, cleats, braces, foreguys, etc. and see how closely the theoretical matches reality. It may be a keeper, but I’m still planning to fabricate a final version out of 3.5” OD 6061 aluminum tubing.