What are these screw things called

[thinwater]

Just three thoughts:

1. I've seen some very badly corroded aluminum rivets. The worst was used to attach a stainless internal backer for boom main sheet attachments and similar (not my boat). They all failed and the backer moved. Just as people worry that stainless will cause corrosion of the aluminum spar, if the aluminum touches a stainless part the rivet corrodes. So I will offer that aluminum rivets ONLY make sense when ALL of the connected parts are aluminum. Simple logic.

2. Seldon and all of the spar makers specify monel. I'm pretty sure they are the experts.

3. My early 80s beach cat is still held together with monel rivets. It's spent a lot of time on the beach. No problems with the rivets. I have drilled out and replaced a few when replacing hardware; the hole was always reusable.

I have also used a lot of stainless rivets. I've never noticed significant corrosion or any difference from monel, but it is accepted that monel is better.

 

[rgranger]

Now you have me wondering about the aluminum backing plates that most Hunter boats have embedded in the fiberglass deck that holds a lot of the deck hardware in place. Most of the bolts going into those backing plates are stainless.

 

[thinwater]

Now you have me wondering about the aluminum backing plates that most Hunter boats have embedded in the fiberglass deck that holds a lot of the deck hardware in place. Most of the bolts going into those backing plates are stainless.

It is a pretty safe bet that the bolts are seized beyond all non-destructive attempts at removal. A common problem. Most commonly people remove the old hardware, cut the bolts off flush, and drill new holes 1" away. You could hope you hit the plate and tap the hole, or you can install nuts.

 

[dlochner]

Do your engineering then.

https://en.wikipedia.org/wiki/Shear_stress

Stress versus Shearing force.

Titanium for the Win !!

Jim...

Jim, I didn't say anything about stress or force, I said strength or the ability (in this case) of the rivet to stand up to a force applied at a right angle to the axis of the rivet.

If you are going to criticize a comment, at least get the context correct.

 

[dLj]

Titanium for the Win !!

There is no magic bullet.

Titanium has benefits and limitations, just like all other materials.

dj

 

[rgranger]

It is a pretty safe bet that the bolts are seized beyond all non-destructive attempts at removal. A common problem. Most commonly people remove the old hardware, cut the bolts off flush, and drill new holes 1" away. You could hope you hit the plate and tap the hole, or you can install nuts.

Well that would make sense! Except that while trying to trace down a leak into my head compartment I rebeded all the stanchions and deck organizers and winches on my Hunter 26 and I had no trouble removing the stainless steel bolts and putting them back in. However I admit that seems counterintuitive.

 

[jviss]

This is an interesting discussion to me, as I like the controversy, and it seems people have preferences that aren't informed by mechanical engineering principles.

For something like the OP's application, the rivet's shear strength isn't at issue; what you want it a really good fit between the cleat and the boom. The rivets pull those two together and the friction between the cleat and the boom is what provides the strength in this application. So, the rivet is providing the strength in tension to create this friction. So it's likely that an aluminum rivet would be sufficient. Regardless of that, I've standardized on stainless rivets and use copious amounts of Tef-Gel when I use them in aluminum. I also insulate the mating surfaces if they are dissimilar metals, like stainless steel and aluminum, with thin, white tape or Tef-Gel.

 

[shemandr]

So... I'm the least expert of these posters but I have an engineer friend who is a sailer - primarily of catamarans.
He's had this discussion among his cat sailers. He insists that aluminum rivets are preferable over other materials as long as the quality of the aluminum alloy is high. I know nothing about aluminum alloys. He said that you are not going to get these rivets at the hardware store but they are available from other venders.
So according to his view it's not so much the material but the quality of the material.

 

[dLj]

So... I'm the least expert of these posters but I have an engineer friend who is a sailer - primarily of catamarans.
He's had this discussion among his cat sailers. He insists that aluminum rivets are preferable over other materials as long as the quality of the aluminum alloy is high. I know nothing about aluminum alloys. He said that you are not going to get these rivets at the hardware store but they are available from other venders.
So according to his view it's not so much the material but the quality of the material.

I'd be interested in knowing what the "quality" aluminum rivets are.

But from all I've seen, the preferred material for rivets is monel when connecting stainless fittings to aluminum masts. Monel does not have the reactions with the complex structure from rivet head through internal contacts in the aluminum mast.

When I had a stainless fitting put on my aluminum mast for a whisker pole connection, they used a plastic sheet under the fitting, and went through the fitting, plastic insulator and into the mast with monel rivets. This was stated to be the best method for connection strength and long term stability of the connection.

I don't see how you can effectively isolate the fastener at all points of contact; the head against the fitting, and the contact with the backside inside the aluminum mast as well as all points in-between.

It would seem that if you are attaching an aluminum fitting, then good quality aluminum rivets could be a better choice, but i don't find aluminum fittings to be the norm.

dj

 

[jviss]

I'd be interested in knowing what the "quality" aluminum rivets are.

But from all I've seen, the preferred material for rivets is monel when connecting stainless fittings to aluminum masts. Monel does not have the reactions with the complex structure from rivet head through internal contacts in the aluminum mast.

When I had a stainless fitting put on my aluminum mast for a whisker pole connection, they used a plastic sheet under the fitting, and went through the fitting, plastic insulator and into the mast with monel rivets. This was stated to be the best method for connection strength and long term stability of the connection.

I don't see how you can effectively isolate the fastener at all points of contact; the head against the fitting, and the contact with the backside inside the aluminum mast as well as all points in-between.

It would seem that if you are attaching an aluminum fitting, then good quality aluminum rivets could be a better choice, but i don't find aluminum fittings to be the norm.

dj

I've done a lot stainless to aluminum attachments, and using thin white tape between them, and Tef-Gel on stainless rivets or screws seems to work very well, and the screws are removable years later.

 

[dLj]

I've done a lot stainless to aluminum attachments, and using thin white tape between them, and Tef-Gel on stainless rivets or screws seems to work very well, and the screws are removable years later.

Are you wrapping the rivets in the tape then inserting and riveting?

dj

 

[jviss]

Are you wrapping the rivets in the tape then inserting and riveting?

dj

No, I just use the brush that comes with Tef-Gel to thoroughly coat the hole with it.

 

[dLj]

No, I just use the brush that comes with Tef-Gel to thoroughly coat the hole with it.

How do you get the inside surface of the mast? You feel the Tef-gel does that?

So from a production point of view, you are taking a lot more time with each river than by using a monel rivet. You are also relying on the Tef-gel to make a complete coating - not always is going to be as consistent. Sure that sounds like it could work, but it still seems to me like a monel rivet is still a better option. Of course, for a DIYer your system should work. There is the added aspect of sourcing monel rivets compared to SS. So seems to be a matter of preference. Lots of things can work.

I'd like to hear more about the use of aluminum rivets and best practices.

You'd thrown in screws also above. That's s separate issue in my mind. I don't like using screws into aluminum for permanent structural connections, only for connections that you want to take on and off.

dj

 

[jviss]

How do you get the inside surface of the mast? You feel the Tef-gel does that?

So from a production point of view, you are taking a lot more time with each river than by using a monel rivet. You are also relying on the Tef-gel to make a complete coating - not always is going to be as consistent. Sure that sounds like it could work, but it still seems to me like a monel rivet is still a better option. Of course, for a DIYer your system should work. There is the added aspect of sourcing monel rivets compared to SS. So seems to be a matter of preference. Lots of things can work.

I'd like to hear more about the use of aluminum rivets and best practices.

You'd thrown in screws also above. That's s separate issue in my mind. I don't like using screws into aluminum for permanent structural connections, only for connections that you want to take on and off.

dj

The brush for the Tef-Gel is like a little umbrella, and leaves some on the inside surfaces. Plus, you can dip the rivet in it, if you want.

I wouldn't even know where to look for monel pop rivets! Plus, some high strength applications, like the 3,000 psi rivets for Catalina mast tangs, are only available in stainless.

Yes, screws for removable things, like mast gates, etc.

 

[dLj]

The brush for the Tef-Gel is like a little umbrella, and leaves some on the inside surfaces. Plus, you can dip the rivet in it, if you want.

I wouldn't even know where to look for monel pop rivets! Plus, some high strength applications, like the 3,000 psi rivets for Catalina mast tangs, are only available in stainless.

Yes, screws for removable things, like mast gates, etc.

An interesting post... First you say you have no idea where to get monel rivets, then say they don't make them for a specific application... Seems be be kind of a logic gap there..

In any case, I'm not trying to have a "I'm right you're wrong" kind of discussion but rather a congenial informative type of discourse. There are many ways to get things done. It's good to hear how things do and don't work...

If you'd like to learn where to get monel rivets the easiest place to look first is McMaster-Carr... They have some of the more common sizes...

dj

 

[jviss]

An interesting post... First you say you have no idea where to get monel rivets, then say they don't make them for a specific application... Seems be be kind of a logic gap there..

In any case, I'm not trying to have a "I'm right you're wrong" kind of discussion but rather a congenial informative type of discourse. There are many ways to get things done. It's good to hear how things do and don't work...

If you'd like to learn where to get monel rivets the easiest place to look first is McMaster-Carr... They have some of the more common sizes...

dj

No, both things I said are true, and not logically inconsistent or contradictory. Find me a Monel rivet that's rate 3,000 psi tension and 3,000 psi shear, that fits in the holes of the C36 mast tangs.

I had to special order these from Cherry when I was making a new mast for the C36.

 

[dLj]

No, both things I said are true, and not logically inconsistent or contradictory. Find me a Monel rivet that's rate 3,000 psi tension and 3,000 psi shear, that fits in the holes of the C36 mast tangs.

I had to special order these from Cherry when I was making a new mast for the C36.

Ah, I now see what you were saying. I'm sure there are specific applications where one type of rivet is the only kind available.

I was just talking in general terms of preferred materials. Aluminum, stainless and monel will all work - my experience has been that monel tends to work better over other materials in general especially when there are multiple materials being used connecting to an aluminum mast.

In your specific case the rivets needed were only in stainless.

Just a note - any material used would not have the same tensile and shear strength. If a supplier told me differently, I'd have to ask for more detailed data justifying that claim - sounds more like a marketing claim than an engineering claim. In general, the shear strength is about 0.6 of the tensile strength. Ball park number...

I'd love to get the info that @shemandr stated about aluminum rivets.

dj

 

[jviss]

If a supplier told me differently, I'd have to ask for more detailed data justifying that claim - sounds more like a marketing claim than an engineering claim.

I spoke directly with an engineer at Cherry Rivet. He really knew his stuff! When I lamented that the smallest quantity of those rivets that they sold was 50, and it was prohibitively expensive for me, since he knew I am an engineer, too, he asked "how many do you need for your evaluation of our product, as samples?" I said 12, and he said he'd send me 13 if I paid for shipping. Sweet! So, yes, they really are 3kpsi shear and 3kpsi tension, per their spec and this engineer. BTW, I had to buy a $120 rivet puller for these, with 2' long handles.