Here is a related question. My Imron-painted aluminum mast and boom has the
usual assortment of fittings and attachment methods typically found on a
twenty-year-old boat now on it's fourth or fifth owner. For the most part
the paint is in good condition, (and stainless bolts protected with TefGel
or similar) but here and there next to older stainless fittings, or around a
weld there are the usual smaller-than-a-pea pustules of corrosion. Sooner or
later I plan to have the entire mast repainted professionally but in the
meantime what is the best etch/prime/paint touchup method to minimize
continuing damage? I assume there is a more or less standard sequence and
bill of materials used by aircraft or aluminum boat maintenance shops. Any
suggestions re online or local vendors would be much appreciated.

Scott
S/V Itchen

Brian Whatcott wrote:
On Sun, 27 May 2007 20:26:14 -0400, Dan "dhapp-at-wmis,net" wrote:

Brian Whatcott wrote:

Aluminum riv-nuts are easily obtained, easily fitted, and reasonably
replaceable when the time comes. Screw a SS screw into a riv-nut
Brian, do you have a link to a source for these riv-nuts? I can't seem
to find them.

I googled "riv-nut" for 30,000 hits.
I googled "riv-nut supplier" for 3000 hits.
Here is one of them. It has a cross-section diagram to give you the
idea

http://www.cardinalcomponents.com/fasteners.htm

Brian Whatcott Altus OK
I see that now. I must have had an blond moment. Thanks for the link,
Dan

CB wrote:
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?

Don't even consider brass if you want any strength. It has none and
is even worse in a salt water environment as it will lose the zinc
that is compounded with copper to make brass.


--

dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

CB,
It is correct to consider the dissimilar metal as an issue, but in this
application, it isn't the major one. This is so because the fastener will
not be subjected to immersion, only wetting. So, in application, the problem
is not so different than on a motocycle case or an aircraft. Stainless in an
anti-seize grease is fine. The bigger issue is the thin wall of the mast.
Rivets are much better and if removing the fastener periodically is an
issue, you should use an aluminum riv-nut riveted in place and then use a
316 screw.
Steve

"CB" wrote in message
ups.com...

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

On Fri, 25 May 2007 18:40:03 +0200, "Steve Lusardi"
wrote stuff
and I replied:

I disagree with ther first bit. If the boat is to be used
_exclusively_ in FW environments, then you may get away with it. But
the OP did mention possible marine trips. Also, a boat by its spidery
nature (don't want to climb the mast) and less industry pressure
compared to even automotive, will tend to get less inspection in
whatever setup.

Also, actual constant immersion can sometime be better than moist
environments....less oxygen and other acids etc.

CB,
It is correct to consider the dissimilar metal as an issue, but in this
application, it isn't the major one. This is so because the fastener will
not be subjected to immersion, only wetting. So, in application, the problem
is not so different than on a motocycle case or an aircraft.


Stainless in an
anti-seize grease is fine. The bigger issue is the thin wall of the mast.
Rivets are much better and if removing the fastener periodically is an
issue, you should use an aluminum riv-nut riveted in place and then use a
316 screw.
Steve

"CB" wrote in message
oups.com...

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

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

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)

--
Posted via a free Usenet account from http://www.teranews.com

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)

--
Posted via a free Usenet account fromhttp://www.teranews.com

On 27 May 2007 10:55:18 -0700, CB wrote:


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

Riv-nuts cost peanuts and go on with a pop rivet gun.

But if you were paranoid about electrolytic corrosion, there is a
species of rubber expanding nut with an internal metal threaded
insert. That might suit some low strength applications too.

Brian Whatcott Altus OK

Brian Whatcott brought forth on stone tablets:
On 27 May 2007 10:55:18 -0700, CB wrote:



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


Riv-nuts cost peanuts and go on with a pop rivet gun.

But if you were paranoid about electrolytic corrosion, there is a
species of rubber expanding nut with an internal metal threaded
insert. That might suit some low strength applications too.


Indeed. These are commonly used (or were...) for mounting air
conditioner condensers in cars, where galvanic corrosion is also a
problem. Unfortunately, however, the only ones I have seen have the
threaded insert made of brass. Not a good choice in a marine environment.

bob
s/v Eolian
Seattle