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Stronger aluminium rivets?


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More aluminium mast stuff! 

We tend to sail in the upper wind range of our Nacra 15. Right on the heels of a recent windy race (which we won) we went out to train in 20+ knots and... broke the cunningham! The rivets came right out from our pulling. 

As much as I'd like to use this episode to pretend... I'm no Mr Universe or Mr Muscle. And yet, I don't want to size up on the rivets – the size is what the PXR swivel mount takes.

For a given rivet size, are there stronger-spec rivets... in aluminium material? Or is there a metal that's non-reactive with aluminium (and saltwater), and stronger?

(Why did we break this thing? because the N15 has a stupid telephone pole of a mast instead of a modern tapered CF mast, so when it gets windy you have to crank the sh_t out of the cunningham. This abuses the cunningham, the main sail, sailors hands, etc. Nacras and 49ers need some cross pollination, urgente...)

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There are S/s rivets. There is a rule about marine use regarding whether you want to destroy the mast or the rivet when the eventual failure occurs. Regardless, use a backing plate about the same thickness as the mast material. 

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3 minutes ago, El Borracho said:

There are S/s rivets. There is a rule about marine use regarding whether you want to destroy the mast or the rivet when the eventual failure occurs. Regardless, use a backing plate about the same thickness as the mast material. 

I have SS rivets in my toolbox. But they'll react against aluminium. 

The breakage we had was that I popped the 'head' of the rivets. The rivets were well "popped" and drilling them out after was real work. 

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If you slather stainless rivets with some sort of anti-seize goop before installing them, you should be good for a long time.  Silicon caulk will work.  Tef-Gel works very well but is expensive.  If you routinely sail in high wind conditions, how long is your spar going to last anyhow?  5 years?  Gooped stainless rivets will be fine for 5 years.

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 I use Monel rivets, they are non reactive, stronger than aluminium, weaker than stainless steel and when you pop them the head molds nicely to the mast shape. I still add duralac to be sure 

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6 hours ago, martin 'hoff said:

More aluminium mast stuff! 

We tend to sail in the upper wind range of our Nacra 15. Right on the heels of a recent windy race (which we won) we went out to train in 20+ knots and... broke the cunningham! The rivets came right out from our pulling. 

As much as I'd like to use this episode to pretend... I'm no Mr Universe or Mr Muscle. And yet, I don't want to size up on the rivets – the size is what the PXR swivel mount takes.

For a given rivet size, are there stronger-spec rivets... in aluminium material? Or is there a metal that's non-reactive with aluminium (and saltwater), and stronger?

(Why did we break this thing? because the N15 has a stupid telephone pole of a mast instead of a modern tapered CF mast, so when it gets windy you have to crank the sh_t out of the cunningham. This abuses the cunningham, the main sail, sailors hands, etc. Nacras and 49ers need some cross pollination, urgente...)

 

Typically Nacra do use Monel rivets in both the carbon and alloy rigs but maybe for the N15 they tried to save some money... Have you contacted either the dealer you bought the boat through or Nacra directly? I'm pretty sure they would tell you what it is to be sure. Maybe even claim warranty if it was manufacturer error. 

If you're not worried about staying one-design, consider upgrading to this https://www.harken.com/en/shop/carbo-air-blocks-291/40-mm-pivoting-lead-block-cam-matic-cleat/ 

The PXRs tend to be fidgety and the spacing between fasteners holes is much closer together and seems to get levered off the rigs easier during hard sailing. Either way, use monel rivets when re-installing and coat liberally in tef-gel. You should be keeping a tub of the stuff in your tool kit for the beam bolts already. 

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4 hours ago, madboutcats said:

 I use Monel rivets, they are non reactive, stronger than aluminium, weaker than stainless steel and when you pop them the head molds nicely to the mast shape. I still add duralac to be sure 

Yea, what that guy said

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11 hours ago, martin 'hoff said:

I popped the 'head' of the rivets. The rivets were well "popped" and drilling them out after was real work. 

This suggests to me that the rivet was not down tight before being set and the fitting could "work" back and forth to fatigue the head off.

No picture, but I'd guess the fitting was cantilevered out into space and the far rivet failed ...

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The cantilever puts the far fastener in tension not shear. Pop rivets are really bad at tension. I'd use a SS machine screw and nylon lock nut with your favorite smoodge.

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So tefgel is enough to keep a small SS rivet on an alum mast from reacting in for a couple years? Well damn should have told me earlier! :-)

That's the ticket then. I have tefgel and SS rivets, was only missing this insight. 

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You could go with a cherrymax or cherrylok type fastener, or an olympic type rivet (from our airstream friends)

But they all require more specialized installation tools...

SS with a corrosion inhibitor or monel is probably a good compromise.

 

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On 1/18/2022 at 7:01 AM, Pro looper said:

Duralac would be better than Tefgel as Tefgel tends to melt W/ a black mast but as I said buzz uses silicone

and I've taken masts apart that are over 30yrs old and have NEVER seen any problems

Almost anything that keeps the salt out of the joint will work fine. I used a lot of silicone, it comes in colors, makes the gaps disappear. And it non - conducting

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On 1/18/2022 at 9:15 PM, CaptainAhab said:
On 1/18/2022 at 4:33 PM, madboutcats said:

 I use Monel rivets, they are non reactive, stronger than aluminium, weaker than stainless steel and when you pop them the head molds nicely to the mast shape. I still add duralac to be sure 

Yea, what that guy said

Plus 1

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