Connections to mast, screws or rivets?

[er9]

What about monel machine screws? Mcmaster has them. Better choice than aluminum machine screws if one didnt want to use rivets? Or is Monel a trade name and the rivets are some special alloy? Mcmaster lists the machine screws as simply a nickel alloy which appears more catholic than stainless.

[CarinaPDX]

Monel is a trade name for proprietary alloys made primarily of nickel (usually 63%) and copper, with about 5% other metals. Before stainless became common it was the preferred metal for many marine parts, including shafts and tanks. It has many desirable properties. See: https://en.wikipedia.org/wiki/Monel The change from stainless being more expensive to being less expensive killed the market for recreational craft.

Greg

[Edit: Monel is not a cupronickel, as it is primarily nickel, not copper. It is properly referred to as a nickel-copper alloy.]

[Pat the Rat]

I suggest looking into a product know as nut serts or riv-nuts. They are a pop rivet type device that leaves a threaded insert. Better than a threaded hole in thin wall aluminum extrusions.

[bobgarrett]

Originally Posted by Clivevon

+1 for monel rivets. much stronger than aluminium.

I realise this is a gross simplification but when I fitted reinforced plastic through-hulls (Trudesign) people asked me whether plastic was strong enough. I replied that since it was a plastic hull it should be sufficient.

Likewise, if you have an aluminium mast why would you need something even stronger to fit in it?

But to repeat where I started I know this is a simplification and not considering design/leverage/stress/strain/stress etc. but just because a material is stronger does not make it automatically better.

[Manateeman]

The original poster is attaching some light stuff. They didn’t say they planned to sail to Patagonia. Strength requirements? Well that depends on what vessel to start with and where is it going.
Monel rivets are nice, so are 316 stainless. If you want to tap and use 316 machine screws, ok...your steaming light isn’t going to hit you on the head.
I’m not big on riv-nuts but they are strong and some professional boatbuilders use them where they want more than a direct tap and machine screw.
I only use Tef-Gel. Plastic under larger parts.
I’m removing all my flanged Marelon Forespar seacocks and going to Stainless Groco adaptors on TIG welded reinforcement plates with 316 industrial valves which have CeraKote interiors. I don’t consider a valve that is not bolted to my hull a seacock. Fine for some to use supported valves I guess. It’s their boat.
And we are back to the start. What boat. Where is it going.
No perfect design, material, construction, nor number of hulls.
Happy trails to you.
Mark, an experienced boatbuilding manatee

[lituya1617]

As a retired aircraft mechanic it shocks me to learn that aluminum rivets don't last. ???
Who knew? Let me assure you that, properly engineered and installed, a riveted joint with aluminum rivets is as good as any method of joining aluminum to aluminum. You have to do it properly, of course. So-called "pop" rivets do not qualify as rivets in my estimation. They are fine for non-critical situations but not at the top of a mast. If it is easy and quick, it probably will not last.

[Jim Cate]

Originally Posted by lituya1617

As a retired aircraft mechanic it shocks me to learn that aluminum rivets don't last. ???
Who knew? Let me assure you that, properly engineered and installed, a riveted joint with aluminum rivets is as good as any method of joining aluminum to aluminum. You have to do it properly, of course. So-called "pop" rivets do not qualify as rivets in my estimation. They are fine for non-critical situations but not at the top of a mast. If it is easy and quick, it probably will not last.

What you say is certainly true... but just how does one use a standard rivet to attach a light fixture half way up a mast with no access to the inside?

I'm not sold on pop rivets (and recommended use of machine screws and tapped holes upthread, much to the disdain of most other respondents), but they were invented for just such applications.

I'm glad that Boeing and other aircraft builders don't use pop rivets to hold the skins on their planes!

Jim

[LouK]

Thanks to all who contributed to this post.

[Sara Tim]

Pan head screws will be better than rivets in this case. Screws deliver convenient disassembly and reassembly while rivets offer economical and reliable fastening. Some advantages of rivets are that, they are resistant to vibration, low-profile heads, and the rapid, low-cost assemblage where more fasteners are required.
In your case, disassembly may be required after you install once. Rivets don’t give this type of feature. That’s the reason you should use pan head screws instead of rivets. They are available on Albany County Fasteners.

[Patrigo]

I have said it before, and I will say it again, RIVNUTS. Why not?

[Manateeman]

Hi. One big reason. First, anything you attach has to be isolated. I use a lot of Tef-Gel and Mylar or other plastic if it’s a large surface area. I TIG anything I can but there are parts you just need to fasten. At some point, no matter how careful you are, the aluminum starts to corrode next to the screw, rivet...whatever. No big deal to me but ...
Some owners want everything removed and the spar repainted so you have to drill out the rivnut. Or...what ever got screwed into the rivnut, is broken inside.
Now you have to drill the rivnut out. If it spins, it’s difficult. If it is on a spot you can’t grind the head off, even more difficult.
They are a great fastening. I see your point and agree. Use Tef -Gel and you will be fine but sometimes you have to think ahead and ask yourself how to remove it, will the hole need to be moved or welded because it’s not going to seat a new rivnut. I’ve seen boatbuilders just stand there trying to figure out all the choices.
No perfect design, material, nor...method...of construction. Anyway...
Happy trails to you.
Mark and his gun toting manatees (TIG guns only unless you call them cows or dugongs)

[Bycrick]

Rivnuts are quick and easy to install. They’re great until a screw corrodes and breaks off. Then you have to drill the screw out of the Rivnut. Worst case is the Rivnut then spins in the mast. Don’t ask how I know.

[andreaswolfman]

Originally Posted by LouK

In the process this weekend of replacing steaming light & VHF antenna, question is which makes more sense, using screws or aluminum rivets to secure to mast?

Look into RivNuts. You can get them in aluminium or stainless. They are essentially threads that you rivit in. They work awesome in most cases.

[BlackHeron]

Easier to drill an aluminum pip rivet out than a stuck stainless fastener. Rivets drill out in no time if you know what you are doing. As fast as removing a threaded fastener.

Rivnuts can still have fasteners corrode into them and are much more of a PITA to remove with or without a stuck fastener.

Give me rivets every time.