Rivets or Machine Screws When Splicing a Mast?

[Baby tug]

Everything on my boat is welded the few things that weren’t welded corroded , brackets for my dinghy are stainless bedded with 5200 , I removed them because i didn’t like anything on my swim platform as i have a transom door and I don’t like to climb in and out of my boat , heavy corrosion underneath the stainless steel bracket , The entire boat is made out of quarter inch aluminum the hull was welded and the weld’s ground flush you can’t even see a seam that was 35 years ago and nothing is cracked or leaking ,My outriggers are welded aluminum pipe ,My radar arch welded aluminum , to the deck no bolts , I don’t care if you bolt another piece of aluminum it will corrode underneath the aluminum salt water does not like fasteners Plain and simple , Railing Welded aluminum , on aluminum boats that I’ve seen with stainless railing because it’s pretty , guess what corrosion ,Like I said The entire hull was welded and ground flush, Mig welded, spray welded which is the hottest welding there is no cracking no leaky, just my experience and my opinion for whatever that’s worth

[neilpride]

Oranges v aples, i dont know what kind of alu specifications are on your boat hull, but most masts this days are 6000 series extrusions, they dont like welds, also , when your hull is assembled with ribs, panels, supports etc,, the result its a rigid structure that does not bend, does not move, and does not have cyclical loads like a mast.

For me, the only correct path is what the majority of manufacturers of aluminum masts advise and recommend. stay away from weldings as much as possible, and its really funny because sometimes they make the uppers tangs in some multihull masts welded, well in fact its a piece of aluminium crossing from side to side ,but i guess they have safe procedures to do that without risks.

So, weld a couple of sections with a sleeve inside, so far for some folks work and they dont have any problem, but i cant see a multihull mast with all the diamonds pulling the stick like a banana with all those loads working against the weld , to risky in my opinion. The same applies to a monohull to a greater extent or even more, the rig of a monohull is less stable compared to a multihull.

[Chotu]

Originally Posted by neilpride

Oranges v aples, i dont know what kind of alu specifications are on your boat hull, but most masts this days are 6000 series extrusions, they dont like welds, also , when your hull is assembled with ribs, panels, supports etc,, the result its a rigid structure that does not bend, does not move, and does not have cyclical loads like a mast.

For me, the only correct path is what the majority of manufacturers of aluminum masts advise and recommend. stay away from weldings as much as possible, and its really funny because sometimes they make the uppers tangs in some multihull masts welded, but i guess they have safe procedures to do that without risks.

So, weld a couple of sections with a sleeve inside, so far for some folks work and they dont have any problem, but i cant see a multihull mast with all the diamonds pulling the stick like a banana with all those loads working against the weld , to risky in my opinion. The same applies to a monohull to a greater extent or even more, the rig of a monohull is less stable compared to a multihull.

Thanks for that explanation. That makes sense. I guess that’s the reason.

Multihull is a different sort of application.

Everything on my mast as welded actually. Just like you are talking about. The Tangs. The supports for the spreaders. The gooseneck. All the hardware that was on there. It’s all welded on.

[Lodesman]

Originally Posted by Boatwright

Monel is said to be less subject to electrolytic corrosion in contact with aluminum than SS.

By whom? I guess it depends on the particular alloys, but I think most Monels are higher on the nobility scale than 316.

[neilpride]

Yes, spreaders brackets welded, but the load its really different , both spreaders are working against each other, sweep back spreaders work different, i mean many stuff its welded in a mast for different applications and its really cool, but cant say the same for a splice.

[Blaujockel]

My boat: 43ft Aluminium long keel, 17.7mtr. mast lenght. first watered 2000. 12 years salty med sea, than atlantic and pacific. Boat is sold now. But the mast ist still working.

I fixed my selfmade maststeps with 7075 aluminium screws. The screws are special annodizised. Wallthickness of mast 3 to 3.2mm. Thread M5. Up to now, no corrosion, no break.
I fixed window frames too. Screw Material 5754 non plated. M6x30.



Same 7075 screws I fixed a cable guide u-tube flat on the deck. Screws was corroded after 8 years. But of course, the salt and water is everytime in these little gaps between the deckparts. I changed against Titanium screws.



A Mast and the window frames will be washed by rain normally. So I expect this is the reason why there is no defect on vertically mounted parts/screws.
Also possibel: Titanium screws. Absolutly no corrosion, very high strenght.

[thinwater]

[QUOTE=RaymondR;3708185 ... It is also a fairly stretchy material and consequently those fastenings closest to the join may experience much higher shearing forces than those spaced further away. The consequences of these circumstances is that progressive failure may occur.[/QUOTE]


This is a subtle and very good point, and is the reason commercial splices have closely spaced fasteners. It is a problem when stitching nylon and bungee materials. Think of playing tug of war with a bungee cord, and the rule that you cannot move your feet. Only the first guy is doing any work, the rest is stretch, until he falls, and so forth. A progressive failure. This is what you see with nylon stitching. Also many pealing failures of adhesives when the flexibility of the two surfaces is different.


The plug can be long, but the fasteners should be relatively closely spaced, not spread over several feet. Many industrial proofs.

[thinwater]

Originally Posted by Chotu

That sounds reasonable. But the rivets are not in any sheer condition at all. They will be in tension.

Would they still be better?

Not true. Think about when there is a bending moment. Shear on both sides unless the epoxy holds and the fit is dead perfect ... in which case you don't need the fasteners.


You will have both shear and tension.

[s/v Jedi]

Originally Posted by Chotu

This is really interesting actually. Why don’t people do this? Why is it always rivets and screws?

Certainly my welder would be a lot more comfortable with this.

Because the aluminium looses the heat treatment which weakens it up to 7 times…. which is a mind boggling number

[Chotu]

Originally Posted by thinwater

Not true. Think about when there is a bending moment. Shear on both sides unless the epoxy holds and the fit is dead perfect ... in which case you don't need the fasteners.


You will have both shear and tension.

I mean, yes. A little bit. But not some great amount of sheer. Just a little. The vast majority is in tension.

Sticking with the machine screws.

They stand up to sheer well, tension great, etc

[stormalong]

Originally Posted by Chotu

This is really interesting actually. Why don’t people do this? Why is it always rivets and screws?

Certainly my welder would be a lot more comfortable with this.

This is done and was brought up here. See posts 17 and 19.

My mast is welded. It has survived 37 years, 130,000 sea miles and a broken forestay chainplate. I am not a welder but obviously it can be welded without destroying it's strength.

[Chotu]

Originally Posted by stormalong

This is done and was brought up here. See posts 17 and 19.

My mast is welded. It has survived 37 years, 130,000 sea miles and a broken forestay chainplate. I am not a welder but obviously it can be welded without destroying it's strength.

I remember that line of discussion. What I don’t understand is why everyone has a different opinion. This sucks.

The easiest thing would be to weld it. I have a welder working on it.

The majority here say that machine screws are better.

Second place minority says that rivets are better.

What the hell? This is crazy. There’s no answer to this.

There should be a right way and a wrong way to do this.

But nobody’s mask falls apart. The only thing that we have heard about falling apart is the boom. Done with machine screws.

Yet machine screws are the most recommended item in the thread.

My frustration level is getting pretty high because there’s no answer. But there should be an answer. He is finished making the section tomorrow. He’s going to be starting whatever the next day. I need to figure this out.

I really wish we could do welding. Because it would be easy and he knows how to do it really well. That’s his main business.

But it seems like machine screws have won out in the thread. That’s kind of a good pun. Ha ha

[thinwater]

Originally Posted by Chotu

I mean, yes. A little bit. But not some great amount of sheer. Just a little. The vast majority is in tension.

Sticking with the machine screws.

They stand up to sheer well, tension great, etc

You're going to be fine. This is just a mental exercise.

[thinwater]

Originally Posted by stormalong

...but obviously it can be welded without destroying it's strength.

No, anecdotal evidence is not proof. If it is rigged correctly, the splice was never strained near the limit. It may be several times weaker and you would never know. It's called a safety factor, probably 4-5:1, which engineers allow for wear, fatigue, and mistakes.

[Chotu]

Originally Posted by thinwater

You're going to be fine. This is just a mental exercise.

Well, I was a physicist. But I was never an engineer. Ha ha.

You guys were different than us in the lab.

I wonder how you viewed us. You guys seemed very practical and reserved to me.

I feel like we probably came across as artists/dreamers with math/MatLab. Ha ha.