Simple hollow 12' stayed mast

[Philip Maynard]

I needed a 12' stayed mast and I had left over doug fir 2X and 1X and a wanted to use them to make a simple hollow mast. Cutting a V groove in the 2X and then gluing on the 1X made a triangular hollow core without a lot of effort. Of course I did not save much weight but I am happy with the result. Here is a link to a 500kb pdf with pictures and description.

http://www.pmaynard.lunarpages.com/t...20pictures.pdf

[esingleman]

Looks nice, but I am wondering if the notch caused by the vertices of those triangles is going to be enough of a stress concentration to cause the ligament to split when the mast bends.

[David G]

I'm wondering why hollow? Perhaps I'm missing something, but it seems like a solid mast that size would be light & easy enough to step... and a bit easier to build. Are you, perhaps, trying to build in a calculated amount of flex? Do you want it hollow for internal wiring for the big radar antenna, and internal halyards for the main, jib, flag & signal flags? <G>

Seriously, those three areas (where the wall thickness is approx. 3/8") are going to be weak points. As mentioned, because of the rapid decrease in wall thickness at those 3 spots, they'll be stress risers. Also it's not a lot of gluing surface for something subject to the types of dynamic loads that a mast is. The only saving grace is that with a 12' stick, you'll not be hoisting a huge sail, so overall loads will be smallish. Still - I think, unless there's some strong reason for hollow, I'd do the glue up solid.

"Although prepared for martyrdom, I prefer that it be postponed" -- Winston Churchill

[Philip Maynard]

Of course, it would be much easier to build it solid, and those notches are stress concentrations (thinnest wall sections - that was one reason I shaped the exterior somewhat triangular in section so it would not vary in thickness so much as if I left it round). I was not building it hollow to hide any internal wires, halyards, etc nor was I trying to give it flex. I would not have used it for an unstayed mast which must have 4 or 8 X the stress. I did it for the challenge of doing something different and with a 64SF sprit and 22SF jib I have not seen any flex - (not that I was looking for any or expected to see any) and I have had it out in stronger winds than I wanted to be sailing in and it has been just fine. This design has a pretty narrow application as it is limited as drawn to 2 1/4" diameter - so I would not go higher than 12' and of course the weight savings are minimal in these sizes so most builders would simply go solid. But it was fun to figure it out and worked for me.

Here's the boat, a modified Bluegill

[David G]

Philip - Fun. I guess I've spent too long in job-shop manufacturing. My first thought is always what's quickest & easiest without sacrificing quality or function. However, that can be limiting. It's neat to see experimentation. It's noodling like that which can lead to nifty innovations. BTW, those are some nice drawings.

"To avoid situations in which you might make mistakes might be the biggest mistake of all" -- Peter McWilliams