It failed at the vang attachment point. We simply pulled it out of the boom.
Hi Blaise:
I really don't have a solution to contribute, but I am curious about the vang attachment point that failed on you; since I probably have the same boom design on my 1980 H36.
In the attached photo, is it that little fitting that protrudes from the underside of the boom just aft of the drooping loop of plain white line? When I bought my boat, nothing was attached to it. And the boat never had a boom vang. I had considered using the fitting for this purpose, but because only a very small area of 30 year old 1/8" aluminum was its anchor, I had some doubt that it would be a good idea to attach anything stressful to it. Instead, I decided to drill some holes in the boom for bale attachments. I had salvaged a few bales from a boom that was left next to my boat yard's dumpster a few years before ... so I did the boom bang with two bales on the boom to further distribute the load. Probably over-kill, but the extra expense was the only cost of a 3/8" carriage bolt.
Sorry about your boom ... Last year a J-boat (probably about 32') up the slipway from me suffered a bad break on its boom. A new aluminum (I'm pretty sure it was aluminum) sleeve was welded over it to repair. But I'm sure you have already determined this isn't an option in your case.