Thursday, April 07, 2016

QUIDNON: Mast Tablernacles Rethought

Sometimes delays are helpful because they allow more time for examination, and for rethinking parts of the design. And so it was with the tabernacle design. My initial plan was to use a joint that transferred all of the tension and compression loads into sheer loads on two large bolts, which I called “Jesus bots,” after the “Jesus nuts” that hold helicopter rotors in place. But then Alan, who is designing a boat similar to QUIDNON—a houseboat that sails, but for inland waterways—pointed out that my design would require extremely high precision in the way the components are fitted, or they would start to move and flex under load, and fail. Alan has lots of experience in aerospace engineering, and a keen appreciation for structural elements. What he proposed was two flanges bolted together, connected by a hinge on one side. This approach is very standard: look at your average streetlight, and that's how it's mounted. It is so standard that it doesn't require any interesting structural analysis: one can simply look it up and plug in the numbers. Since the bolts that hold the two flanges together are subjected only to tension loads, they don't need to be fitted precisely, and the math for sizing them is simple.