In a 7, maybe 10 knot wind we had a flying hull and a few seconds later heard a loud BANG--and the mast dropped.

Upon inspection, all rivets had broken off clean. They were not ripped out of the holes, they just broke.

It's possible that there was some minor movement as the mast hound was not a snug fit, but all the same I find it bewildering that a few flimsy aluminum rivets are supposed to hold the entire load, which is probably a ton in a high wind.

Any ideas? Similar experiences?

Unless someone has a better advice, I will use a 1/4 inch bolt for the top rivet holes, a single one that goes through the mast, and drill at least 6 more holes to take additional rivets. Also make it the mast hound a better fit first.

They should not have been ALUMINUM RIVETS, if someone replaced the original ones with aluminum, they caused the problem. I have never heard of that many stainless rivets (what they should have been) failing at the same time. Are you sure that they were aluminum, it sure sounds like they were if they failed in that manner.

I am not a engineer but i would think any movement or play in the hound area would be cause for alarm. every tack (or gybe) would put strain and flex and pull on the rivets and would continuously work the part off....

Mast hounds don't fail. Sounds like someone improperly installed it with aluminum rivets. When you put it back on, use a stainless steel 3/16" rivet with a grip range of 1/4" to 3/8". Apply silicone calking or similar to the hole and the rivet before you seat it. Also, take the mast hound and tape it with clear boxing tap or similar (on the back side) and trim it with a razor along all the edges, before you install it. This will help isolate the dissimilar metals and greatly reduce the rate of corrosion over time. Bolts are not necessary. When you have the hound seated calk the outside of the rivets, remembering to squeeze some into the center hole of the rivets. This will seal this area. This type rivet is very strong and much easier to seat than a monel, which can be difficult with out the proper guns.

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Philip
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Thanks for all the tips; I think we solved that issue. We added 6 more (stainless) rivets just to make sure.