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Old 03-02-2012, 17:12   #16
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Re: 304 vs 316 for mast step fasteners

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Originally Posted by barnakiel View Post
What happens if you use monel ones?

I think (?) most of our mast hardware is attached with monel.

b.
Monel is good, better IMO than SS when attaching to Al.
Can't remember the figures but less "dissimilar" than SS and about the same strength as SS (when compared to Al fastenings). Often harder to source and possibly more expensive than SS.
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Old 03-02-2012, 17:47   #17
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Re: 304 vs 316 for mast step fasteners

Doh. Guess that's why they are monel on our mast!

We paid something like USD 2 each in 6 mm size back in NZ.

Anyways my piece of advice to the OP is to remember and punch out the mandrels. Not all of them pop out and then you get plenty of corrosion there very soon.

b.
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Old 03-02-2012, 18:17   #18
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Re: 304 vs 316 for mast step fasteners

I would use good aluminum rivets. SS will cause corrosion and may be less strong soon! Monel is less reactive.But Al on Al is great.
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Old 03-02-2012, 18:24   #19
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Re: 304 vs 316 for mast step fasteners

Quote:
Originally Posted by Wotname View Post
Monel is good, better IMO than SS when attaching to Al.
Can't remember the figures but less "dissimilar" than SS and about the same strength as SS (when compared to Al fastenings). Often harder to source and possibly more expensive than SS.
Quote:
Originally Posted by barnakiel View Post
Doh. Guess that's why they are monel on our mast!

We paid something like USD 2 each in 6 mm size back in NZ.

Anyways my piece of advice to the OP is to remember and punch out the mandrels. Not all of them pop out and then you get plenty of corrosion there very soon.

b.
OK looks like "My Opinion" (above) isn't supported by the rivet manufacturers. On checking up mandrel materials I came across this:
http://www.ajaxfast.com.au/downloads...tsHandbook.pdf
They clearly state that monel (Nickel Copper) should not be used with Aluminium. This contradicts advice I have previously received many years back form several very experienced riggers. However "best practice" by its nature must change and perhaps (probably) I am wrong in suggesting that monel is suitable. It is certainly stronger than SS and in itself corrosion resistant but not so suitable for use with Al.

But I won't be removing all my monel fastners just yet

There is an interesting section in the above link re mandrel material.

FWIW
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Old 03-02-2012, 18:25   #20
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I strongly disagree with aluminum rivets for something as critical as mast steps (ie your life on the line). Aluminum hardware, especially rivets, doesn't have the strength to withstand shearing loads (ie going aloft in chop)

In college we were attaching new spreader brackets to the masts on FJ dinghies and used aluminum rivets.
They all failed within 6 months without warning. we used stainless afterwards and never had a problem.

I just removed all of my mast steps from my Luders 33 mast that were tapped in with stainless machine screws over 2 decades ago, and they were all in good shape and only a few frozen that required effort. tefgel is the key for minimizing interaction issues.
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Old 03-02-2012, 18:42   #21
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Re: 304 vs 316 for mast step fasteners

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Originally Posted by Wotname View Post
Monel is good, better IMO than SS when attaching to Al.
Can't remember the figures but less "dissimilar" than SS and about the same strength as SS (when compared to Al fastenings). Often harder to source and possibly more expensive than SS.
I received the same recommendation from the builder of my boat when I installed eyestraps on my aluminum crossbeam for the trampoline.

I bought 1/4" monel rivets from Rapid Rivet in NY.

You need to use a serious rivet tool for these rivets. I used the Marson 39031 "Big Daddy" tool.
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Old 03-02-2012, 18:58   #22
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And you can't tap out the mandrels because the rivets need them for strength with sheer loading.... Unless you have special types for that.

I would select 316 or A4 stainless steel, tapped into the mast. I would use Permatex blue threadlocker or equivalent instead of tefgel in this case.

ciao!
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Old 03-02-2012, 19:13   #23
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304 is a little bit stronger, but in this application either is just fine. The 304 will rust stain after a few years. If you don't mind that, save a bit and stay with the 304, otherwise pay a bit more and go for the 316. Drill and tap and use Tef Gel. Do not use sheet metal screws! The sharp points will shread your halyards. This a job best done with the rig out of the boat, that is if you are going all the way to the top. Much easier than hanging in a bosuns chair for, what seems like, never ending hours.
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Old 09-05-2013, 22:22   #24
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Re: 304 vs 316 for Mast Step Fasteners

316 will be better to prevent general pitting and corrosion of the screw. Both 304 and 316 will create Galvanic Corrosion between the Stainless and the Aluminium, eating the Aluminium. There will not be much difference between 304 and 316 in this respect so the most important thing you can do is separate or isolate the materials. Tef gel is good as already mentioned, Duralac also will work (but I think Tef Gel is better), see this article here on Galvanic Corrosion which talks about what is happening.
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Old 10-05-2013, 05:08   #25
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Re: 304 vs 316 for Mast Step Fasteners

I'd use machine screws, tapped with a good quality tap (not hardware store: go to the places toolmakers buy taps)

I'd personally go for decent quality 316 (with nice shiny rolled threads) because in small screws like this, stress corrosion cracking is quite an issue from the roots of the threads, and 316 is less prone.

And I further agree with Nick on Tefgel: plus it doesn't hurt to first run a couple of turns* of PTFE thread tape onto each screw, including the underside of the head

(*no more or it'll push all the Tefgel through, and strip itself off)

The biggest advantage over Monel rivets (which would be my second choice):
Machine screws can be removed (and should be#) at every refit to check for weakening - pick a couple of the worst looking ones and bend until break. (Keep a few new screws of the same batch as control samples)

# This is the only way to be sure they do not seize into the holes eventually and become a liability: it's rather difficult drilling out stainless fasteners in a softer substrate, even if you take the mast down first. It might be worth springing for recessed hex fasteners: they're MUCH easier to drill out, as the drill self-centres)
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Old 10-05-2013, 11:39   #26
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Re: 304 vs 316 for Mast Step Fasteners

Welcome aboard Jamieh.

Methinks the OP will have resolved his issue by now unless he procrastinates even more than me . This thread is over 15 months old!
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Old 12-05-2013, 21:36   #27
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Re: 304 vs 316 for Mast Step Fasteners

15 months old, but very educational. My first boat I used monel rivets that the rigger recommended. My next 2 boats I used machine screws, but I dont recall if they were 304 or 316. I never had any trouble with any of them.____Grant.
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