Yard-spar...part 2
This bamboo version of the yard-spar, including the dowel inserts, epoxy filler, fiberglass wrapping and all attached hardware ended up weighing 12.5 pounds. That’s less than what I estimated a similarly sized aluminum tube would weigh, which is a real bonus, since every extra pound we hoist up the mast will increase the dynamic loads on the mast and rigging once the boat gets rocking to and fro out on the water.
Now that I have a strong, sturdy and lightweight spar to attach the head of the sail to, I needed to figure out how to attach all the following:
1) The halyard (the line that raises the sail and keeps the yard-arm balanced horizontally)
2) The braces (the lines on each end of the yard (“yardarm”) which control the spar)
3) Some way to secure the yard-arm to the mast while still allowing it to rotate about, and slide up/down the mast
4) The three grommets/rings at the head (top edge) of the sail...port, starboard and center
5) Some sort of padding to protect the mast when the yard-spar gets to banging against it.
Here’s what I came up with for 1), 3), and 5):
The halyard attaches to the two white loops (top picture) with a simple bowline. I made two versions of the mast attachment loop which were slightly different sizes since I didn’t know exactly how long they should be until I assembled everything at the boat. One loop is spliced double braid, lock-stitched and whipped. The other is simply secured with a reef knot and again, lock-stitched and whipped. To protect the mast, I wrapped the center portion of the yard-spar with some cotton clothesline. I had never whipped a 3.5” bamboo pole, but it works just the same as whipping any rope end. Only one side is done because I didn’t buy enough clothesline. Oh well, another trip to McClendon’s!
Here is the yard-spar partially hoisted with the braces attached. I will also add a backup halyard attachment line at the center of the yard-spar. The center of the sail’s head will attach to this using a soft shackle, and the port and starboard head attach points will connect to the braces using quick disconnect shackles.
If you are interested in the free body diagram, shear force diagram and bending moment diagram, here is a link to that section of the design document:
https://docs.google.com/document/d/1W3XYiaP2WimTIslNXU_52wk01va0YgxlUhcxD0XA3LY/edit#bookmark=id.7ujeuw3cel9g
Now that I have a strong, sturdy and lightweight spar to attach the head of the sail to, I needed to figure out how to attach all the following:
1) The halyard (the line that raises the sail and keeps the yard-arm balanced horizontally)
2) The braces (the lines on each end of the yard (“yardarm”) which control the spar)
3) Some way to secure the yard-arm to the mast while still allowing it to rotate about, and slide up/down the mast
4) The three grommets/rings at the head (top edge) of the sail...port, starboard and center
5) Some sort of padding to protect the mast when the yard-spar gets to banging against it.
Here’s what I came up with for 1), 3), and 5):
The halyard attaches to the two white loops (top picture) with a simple bowline. I made two versions of the mast attachment loop which were slightly different sizes since I didn’t know exactly how long they should be until I assembled everything at the boat. One loop is spliced double braid, lock-stitched and whipped. The other is simply secured with a reef knot and again, lock-stitched and whipped. To protect the mast, I wrapped the center portion of the yard-spar with some cotton clothesline. I had never whipped a 3.5” bamboo pole, but it works just the same as whipping any rope end. Only one side is done because I didn’t buy enough clothesline. Oh well, another trip to McClendon’s!
Here is the yard-spar partially hoisted with the braces attached. I will also add a backup halyard attachment line at the center of the yard-spar. The center of the sail’s head will attach to this using a soft shackle, and the port and starboard head attach points will connect to the braces using quick disconnect shackles.
If you are interested in the free body diagram, shear force diagram and bending moment diagram, here is a link to that section of the design document:
https://docs.google.com/document/d/1W3XYiaP2WimTIslNXU_52wk01va0YgxlUhcxD0XA3LY/edit#bookmark=id.7ujeuw3cel9g