On 27 May 2007 10:55:18 -0700, CB wrote stuff
and I replied:

so are you actually listening to what you have asked about?


Ok so what I've done is tapped it out (yeah it's a fairly thin wall
but this particular application doesn't have any kind of pulling load
on it (it's a stopper in the boom/yoke downhaul slider)) and then put
in an SS screw (probably 316 because my local chandlery is such a
crap place), and I've insulated the connection point not with anti-
seize but with a coating of 3M 4000 that I happened to have lying
around.

Time will tell.. I'm sure it's fine for the application. Thanks for
everyone's comments, especially those regarding the aluminum riv-nuts.
I will look into those for next time.

Cheers,

-CB


On May 27, 10:19 am, Bruce wrote:
On Sun, 27 May 2007 21:52:54 +0800, OldNick
wrote:



On 22 May 2007 19:59:46 -0700, CB wrote stuff
and I replied:

Your geting replys Cb. Hows it goin'g

I need to tap out a 1/4" hole in my mast to 5/16" 18 (no threads in
there right now) and put a machine screw in there.

I have some options in terms of metal types and there have been a
number of discussions about corrosion and so on with SS in contact
with aluminum and how really useless the isolating compounds are in a
sal****er environment etc etc

So what's the metal of choice? I'm seeing brass, SS, silicon bronze,
zinc plated steel.. what's optimal for the aluminum (non-)interaction?
These other discussions don't have a consistent conclusion. (And no
rivets, this is a small job, I really do need the machine screw).

This is a freshwater boat and has been for a long time. However I
wouldn't rule it out of taking it down the east coast one day.

Thanks for any comments,

-CB

In theory you want to use either aluminum or something very close to
aluminum on the galvanic scale. So, in a perfect world you would
purchase an aluminum bolt and use that.

Unfortunately this is not a perfect world and an aluminum bolt is not
very strong, wear resistant, or available (although they are made), so
you go for the next solution and pick a metal close to aluminum on the
galvanic scale. Say, Monel, for example. Locate a monel bolt and use
that. Again, a bit uncommon but available.

Or, you can do what nearly every maker of aluminum spars in the world
does. Use stainless and insulate it as best you can. If it were my
boat I would drill a hole and either tap it or screw in a sheetmetal
screw, depending on the load to be placed on the "bolt", and then
install the screw/bolt using something like 3M 5200 for a
sealant/insulation.

I have stainless bolts installed in both the boom and mast on a 40 ft.
sloop, afloat in salt water, in the tropics, that have been there for
ten years or more with no signs of corrosion to date.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

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