Hi there,
I believe this wheel has already been invented. I'll be in touch with Douglas by PM with scantlings and sources. Meanwhile for general info the flanged bushings we use come in both stainless and aluminum. The aluminum ones are larger, and sit in the mast wall. The stainless ones nest in them, after going through their tangs. So the flange of the aluminum bushing holds the tang off the mast wall (good), while recruiting more aluminum molecules for the shroud load to bear on.
With sufficiently thick mast walls (a judgement call), one can use just the stainless bushings.
In cases where there's a combination of high loads and thin walls, a third component is an option: an insert, fastened above and below the tang hole, into which the bushings fit. All of these options distribute the load over more aluminum than even a very large throughbolt could hope to, and without the bother, potential deformation, or potential fatigue of welding doublers on.
We often retrofit bushings, and sometimes inserts, to older masts, where egg-shaped holes indicate the walls are not up to the loads.All you need is a tapered reamer, to get the hole big enough. If you don't have access to a tapered reamer, you can plug the hole with wood, then use a regular drill bit to enlarge the hole.
Because the stainless bushings go through the tang, the tang must be proportioned to have an unusually large hole for the throughbolt, so don't try retrofitting bushings to standard tangs. On the other hand, with the bushings, one can use an unusually small throughbolt, because you are counting on it only for the relatively minor lateral load; the bushings are taking the shear load.
We also use flanged bushings to fix point-loading issues on chainplates and tang clevis pin holes, in cases where they are sufficiently overbuilt to allow for limited reaming.
Fair leads,
Brion Toss
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