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Old 24-07-2017, 10:06   #1
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What's better for installing aluminum mast steps: rivets or tapped threads?

I'm installing aluminum mast steps on our mast (Catalina 320). Two processes for attaching these - I'm not sure which method to use:

Stainless Steel rivets - probably 3/16" size. yes, I'll need to use Marlube to prevent corrosion due to dissimilar metals.

Tapped threads - the other technique I've seem people use is to drill a slightly undersized hole and then run a tap through it - probably 1/4" x 20 threads. Then Marlube and a 1/4" bolt.


I can see that trying to pull a 3/16 rivet 40 feet above the deck will kinda suck, but I've got a pneumatic riveter, so that might not be too bad. Any other considerations. Although I'd like an easy solution . . . the trump card is "which method would be stronger"?

Any thoughts? Opinions?

(ha ha - asking this group if they have any opinion is kind of a "sure thing"!)

thx, markb
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Old 24-07-2017, 10:39   #2
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

Firstly, it'd take a BIG bribe to get me to install mast steps with the mast up. Too much time in the climbing harness, impossible to get precise alignment of all of the steps. Plus a bunch of other pain in the rear items. And I only mention this as it sounds as if you're wanting to do exactly this.


I'd be seriously tempted to go with tapped in fasteners, fully coated with Blue Loctite, as it's what I'm most familiar with. And for the most part the Loctite does a decent job of preventing corrosion, & an excellent one of making sure the fasteners stay put.


Another option is something like say Monel rivets, preferrably with isolators. But... after reading this thread, some other methods are tempting. Does Loctite protect against galvanic corrosion?
Such as using Duralac instead of Loctite. And or, helicoils. Which the latter are something I've always let someone else install them. So I've little experience with same, other than that in general they do seem to make fastener removal easier, especially when used with Blue Loctite. And as is mentioned in the other thread, this method is pretty much exactly what Harken does with their hardware. Which to me is a good sign. Since I've yet to be let down by a Harken part, or their customer service, knock on wood.
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Old 24-07-2017, 15:36   #3
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

The hot set up these days is a drill & tap combo. With a 10-32 tool in a batt reversing drill, things will go pretty fast. Just be carefull to not go too far as these things will go right through the mast.
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Old 24-07-2017, 15:42   #4
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I installed mast steps on my main mast. Each step used four 1/4" aluminum rivets. I did it with the mast up. It came out great and I would do it the same way again.

BTW no dissimilar metals with aluminum mast, rivets and mast steps.
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Old 24-07-2017, 16:34   #5
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I do it when the mast is out for annual checks.

I use 6mm monel rivets.

Cheers,
b.
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Old 24-07-2017, 16:58   #6
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

Quote:
Originally Posted by Guy View Post
The hot set up these days is a drill & tap combo. With a 10-32 tool in a batt reversing drill, things will go pretty fast. Just be carefull to not go too far as these things will go right through the mast.

I'd still use as large as possible (1/4-20) drill-tap bit and set the clutch low on the drill so it stalls before snapping the bit, but they work well. Just like a normal tap, it helps to forward and reverse every so often to clean the hole.
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Old 24-07-2017, 17:10   #7
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I fitted steps to a 44 ft mast whilst it was up. Fairly straightforward as you start from the bottom and stand on the steps you have installed. A "Lazy Tong" type riveter makes it easier as it applies pressure whilst setting the rivet.
If you use sealed rivets there won't be sharp edges inside to wear your halyards.

Regards,
Richard.
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Old 24-07-2017, 18:59   #8
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I rented a hydraulic rivet gun from a rigger and that made the work much easier. No straining in uncomfortable positions. The next boat I did the drill and tap method and it was not too hard using the steps that I had finished to support myself while drilling the next ones up. I used a bosuns chair and a safety harness and didnt do them all in one session. ____Grant.
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Old 24-07-2017, 22:48   #9
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

Rivets! Rivets! Rivets! in the following preference

1) Monel
2) Aluminium
3) Stainless Steel

Regardless of which MATERIAL you decide on I would put them with DURALAC DURALAC DURALAC available at fishing supply companies and some chandler stores, Trying to educate all yachties they should have a tube in their tool box!!-No I dont work for Duralac it's just a dam good product!!

Duralac is an anti-corrosive jointing compound for use between joints of dissimilar metals. It is in the form of a tough, flexible, yellow paste with low moisture permeability, and contains barium chromate in an inert filler matrix. The barium chromate is only very slightly soluble in water, so it remains in the joint, even in the presence of a considerable flow of water. It has a long useful life because it only becomes active in the presence of conditions which promote corrosion.
Indispensable for the effective sealing of joints between dissimilar metals --- even very active magnesium alloys
Effective at preventing corrosion at stress contact points in similar metals, such as rivets in masts
Protects metals in contact with non-metallic materials such as wood, resins, rubber, etc.
Especially useful in saltwater environments which exacerbate corrosive processes
Conforms to specification DTD 369B

https://www.fisheriessupply.com/sadd...nting-compound.



Cheers Steve
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Old 25-07-2017, 10:01   #10
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

What about aluminium rivnuts?
No corrosion, easy to fit and remove if necessary. I have used them for other purposes on a mast.
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Old 25-07-2017, 10:03   #11
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

Ok, thread question for all of you. I'm installing cam cleats on frp 20 degree wedge risers using 1/4-20 machine screws. The issue, due to the wedge shape, the bolts come out at a 20 (70) degree angle and need to be tapped into a 5mm aluminum deck piece at that angle. The underside is not accessible, so I'm relying on the thread to hold this tight.

At an angle, the bolt thread length is longer, but it's partial threads for a lot of this length and I'm not sure if it's a lot weaker than a typical right angle hole. Any ideas?

Matt
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Old 25-07-2017, 11:01   #12
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I'd use self tapping aluminum screws
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Old 25-07-2017, 11:10   #13
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

The former owner of our boat had used rivets on the mast steps he installed, and a few years later, as they started coming loose. [IIRC, he used SS rivets coated in something to prevent dissimilar metal corrosion, but I don't know what he used...]

He removed them all and installed Aluminum rivet nuts where the rivets were, with SS bolts [1/4" - 20] with blue locktite fastening the same steps in place.

10 years later, no issues and no loose fasteners, but steps can be easily tightened and removed if/as needed.

I have also used rivet nuts in other applications. Very easy to do, and reliable. I keep an assortment onboard- along with the usual pop-rivet collection in aluminum, SS, and Monel...

Best wishes with your project.

Cheers! Bill
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Old 25-07-2017, 12:49   #14
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

Not what you want to hear . . . but the mast steps . . . better off without, and learning how to do the various excellent rock climbing techniques for going up the mast.

The rivet nut suggestion is excellent.

However, this is not really a high load application. Bog generic aluminum pop rivets have a shear strength of 310lbs. Put three of those in and you have a decent safety factor and dont have corrosion. And you can get 'extra strength' aluminum rivets.
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Old 25-07-2017, 13:19   #15
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Re: What's better for installing aluminum mast steps: rivets or tapped threads?

I've used monel rivets with duralac. Whatever you use, don't be happy with the 3 fastener per step approach. Go for 6 fasteners each step.
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