Pop Rivets in Masts

Archives
1

Posted by katorpus (jrb@…>)

My masts are made of carbon fiber, and the external sail track is
aluminum.

Aluminum is way down on the galvanic scale…almost as sacrificial as
zinc.

Any time you’re fastening dissimilar metals together in the marine
environment, you want to strive to use fasteners which are as close as
possible to the material (being fastened) on the galvanic scale.

The further apart the two metals are on the galvanic scale, the higher
the potential for corrosion and the greater the potential “voltage” of
the “battery” which you’ve created. The addition of salt and/or fresh
water completes the “battery”…corrosion results, and what will suffer
is the aluminum (not the stainless steel pop-rivet.)

You WANT the pop rivet to degrade (but not quickly), not the sail track
(or aluminum mast if applicable). I’m experiencing “popping off” of the
heads of the aluminum rivets which were used (originally) to attach the
sail tracks to the masts. I find them all the time on the deck.
Periodically (when I feel like abusing myself), I go up the mast and
knock the remaining rivet body through the mast wall with a punch and
replace the missing rivets…with MONEL rivets.

Passivated stainless steel is WAY up on the galvanic scale…right up
there near gold.

Monel is fairly inert and in the middle of the galvanic
scale…stronger than aluminum pop rivets, and not as deleterious to
the aluminum as the stainless steel.

As an aside…

The (original)cast aluminum stanchion bases on my Freedom were attached
to the toe rail with stainless bolts. The combination of the bolts and
the stainless stanchions “rotted” the castings in very short order. The
through-bolts had “welded” themselves to the toerail with the corrosion
(of the aluminum) which resulted, and there was “poultice corrosion”
between the aluminum stanchion bases and the toe rail. The bases were
actually fractured by the corrosion which developed between them and
the stanchions themselves.

The replacements are stainless and through-bolted with stainless bolts
and nuts (with flat nylon washers where the nut contacts the toerail).

I “insulated” the flat plate of these replacement stanchion bases from
the toerail using multiple layers of heavy rubber self-amalgamating
tape and applied a coating of electrical insulating paste on top of
that before bolting them down. No problems eleven years later…

Granted, there’s less salt water “applied” to the sail track than the
toe rail, but why not use the best thing available? (Later) removal of
the Strong Track to re-fasten the underlying sail track down the road
won’t be an easy task.

2

Posted by Herman and Gail Schiller (hschiller2@…>)

Where did you get your supply of monel rivets? Herm

At 02:16 PM 10/11/2008, you wrote:

My masts are made of carbon fiber, and the external sail track is
aluminum.

Aluminum is way down on the galvanic scale…almost as sacrificial as
zinc.

Any time you’re fastening dissimilar metals together in the marine
environment, you want to strive to use fasteners which are as close as
possible to the material (being fastened) on the galvanic scale.

The further apart the two metals are on the galvanic scale, the higher
the potential for corrosion and the greater the potential “voltage” of
the “battery” which you’ve created. The addition of salt and/or fresh
water completes the “battery”…corrosion results, and what will suffer
is the aluminum (not the stainless steel pop-rivet.)

You WANT the pop rivet to degrade (but not quickly), not the sail track
(or aluminum mast if applicable). I’m experiencing “popping off” of the
heads of the aluminum rivets which were used (originally) to attach the
sail tracks to the masts. I find them all the time on the deck.
Periodically (when I feel like abusing myself), I go up the mast and
knock the remaining rivet body through the mast wall with a punch and
replace the missing rivets…with MONEL rivets.

Passivated stainless steel is WAY up on the galvanic scale…right up
there near gold.

Monel is fairly inert and in the middle of the galvanic
scale…stronger than aluminum pop rivets, and not as deleterious to
the aluminum as the stainless steel.

As an aside…

The (original)cast aluminum stanchion bases on my Freedom were attached
to the toe rail with stainless bolts. The combination of the bolts and
the stainless stanchions “rotted” the castings in very short order. The
through-bolts had “welded” themselves to the toerail with the corrosion
(of the aluminum) which resulted, and there was “poultice corrosion”
between the aluminum stanchion bases and the toe rail. The bases were
actually fractured by the corrosion which developed between them and
the stanchions themselves.

The replacements are stainless and through-bolted with stainless bolts
and nuts (with flat nylon washers where the nut contacts the toerail).

I “insulated” the flat plate of these replacement stanchion bases from
the toerail using multiple layers of heavy rubber self-amalgamating
tape and applied a coating of electrical insulating paste on top of
that before bolting them down. No problems eleven years later…

Granted, there’s less salt water “applied” to the sail track than the
toe rail, but why not use the best thing available? (Later) removal of
the Strong Track to re-fasten the underlying sail track down the road
won’t be an easy task.

3

Posted by katorpus (jrb@…>)

— In FreedomOwnersGroup@yahoogroups.com, Herman and Gail Schiller
<hschiller2@…> wrote:

Where did you get your supply of monel rivets? Herm

I ordered them through an amazing hardware/lumber store in Rockport, TX
named “Bracht’s”…but they are available online.

Google monel pop-rivet and you’ll find some sources…most seem to be
in the U.K. or Australia, but I found this one…in California…and it
has a handy table of the strengths of given sizes of various pop rivets.

Note: You want the ones with the STAINLESS steel mandrel (which will be
insulated from the aluminum by the monel body.

The monel/stainless rivets have twice the tensile strength of the
aluminum ones (shear strength is largely irrelevant, given that the
forces are trying to pull the track OFF of the mast, not slide it up or
down)

By my recollection, the cost is about twice that of the aluminum and
near the same as the stainless steel ones.

http://www.hansonrivet.com/w19a.htm

Defender has monel staples for your staple gun if you need any of those
for various reasons…but they don’t stock the pop-rivets.

4

Posted by daniel.oshaughnessy (daniel.oshaughnessy@…>)

Hi Katorpus and thanks for the advise.

Just to put you in the picture, the “Strong” mast track is made of a
very durable plastic.

I drilled out some rivets, which were securing the saddles about 12’ up
the masts, and found no loosness or other signs of corrosion. The masts
are from 1981 and I could see no sign/scar of replacement since
installation.

The Strong mast track is available from Tidesmarine


— In FreedomOwnersGroup@yahoogroups.com, “katorpus” <jrb@…> wrote:

My masts are made of carbon fiber, and the external sail track is
aluminum.

Aluminum is way down on the galvanic scale…almost as sacrificial as
zinc.

Any time you’re fastening dissimilar metals together in the marine
environment, you want to strive to use fasteners which are as close as
possible to the material (being fastened) on the galvanic scale.

The further apart the two metals are on the galvanic scale, the higher
the potential for corrosion and the greater the potential “voltage” of
the “battery” which you’ve created. The addition of salt and/or fresh
water completes the “battery”…corrosion results, and what will
suffer
is the aluminum (not the stainless steel pop-rivet.)

You WANT the pop rivet to degrade (but not quickly), not the sail
track
(or aluminum mast if applicable). I’m experiencing “popping off” of
the
heads of the aluminum rivets which were used (originally) to attach
the
sail tracks to the masts. I find them all the time on the deck.
Periodically (when I feel like abusing myself), I go up the mast and
knock the remaining rivet body through the mast wall with a punch and
replace the missing rivets…with MONEL rivets.

Passivated stainless steel is WAY up on the galvanic scale…right up
there near gold.

Monel is fairly inert and in the middle of the galvanic
scale…stronger than aluminum pop rivets, and not as deleterious to
the aluminum as the stainless steel.

As an aside…

The (original)cast aluminum stanchion bases on my Freedom were
attached
to the toe rail with stainless bolts. The combination of the bolts and
the stainless stanchions “rotted” the castings in very short order.
The
through-bolts had “welded” themselves to the toerail with the
corrosion
(of the aluminum) which resulted, and there was “poultice corrosion”
between the aluminum stanchion bases and the toe rail. The bases were
actually fractured by the corrosion which developed between them and
the stanchions themselves.

The replacements are stainless and through-bolted with stainless bolts
and nuts (with flat nylon washers where the nut contacts the toerail).

I “insulated” the flat plate of these replacement stanchion bases from
the toerail using multiple layers of heavy rubber self-amalgamating
tape and applied a coating of electrical insulating paste on top of
that before bolting them down. No problems eleven years later…

Granted, there’s less salt water “applied” to the sail track than the
toe rail, but why not use the best thing available? (Later) removal of
the Strong Track to re-fasten the underlying sail track down the road
won’t be an easy task.

5

Posted by michel.capel (michel.capel@…>)

John,

Thanks for your excellent piece of advice. Your damage report on the
stanchion bases sounds very familiar. I used new aluminum bases and
insulated the bolts and flat surfaces with paste and nylon washers. Or
actually, that’s what the yardman did.

Michel



— In FreedomOwnersGroup@yahoogroups.com, “katorpus” <jrb@…> wrote:

My masts are made of carbon fiber, and the external sail track is
aluminum.

Aluminum is way down on the galvanic scale…almost as sacrificial as
zinc.

Any time you’re fastening dissimilar metals together in the marine
environment, you want to strive to use fasteners which are as close as
possible to the material (being fastened) on the galvanic scale.

The further apart the two metals are on the galvanic scale, the higher
the potential for corrosion and the greater the potential “voltage” of
the “battery” which you’ve created. The addition of salt and/or fresh
water completes the “battery”…corrosion results, and what will suffer
is the aluminum (not the stainless steel pop-rivet.)

You WANT the pop rivet to degrade (but not quickly), not the sail track
(or aluminum mast if applicable). I’m experiencing “popping off” of the
heads of the aluminum rivets which were used (originally) to attach the
sail tracks to the masts. I find them all the time on the deck.
Periodically (when I feel like abusing myself), I go up the mast and
knock the remaining rivet body through the mast wall with a punch and
replace the missing rivets…with MONEL rivets.

Passivated stainless steel is WAY up on the galvanic scale…right up
there near gold.

Monel is fairly inert and in the middle of the galvanic
scale…stronger than aluminum pop rivets, and not as deleterious to
the aluminum as the stainless steel.

As an aside…

The (original)cast aluminum stanchion bases on my Freedom were attached
to the toe rail with stainless bolts. The combination of the bolts and
the stainless stanchions “rotted” the castings in very short order. The
through-bolts had “welded” themselves to the toerail with the corrosion
(of the aluminum) which resulted, and there was “poultice corrosion”
between the aluminum stanchion bases and the toe rail. The bases were
actually fractured by the corrosion which developed between them and
the stanchions themselves.

The replacements are stainless and through-bolted with stainless bolts
and nuts (with flat nylon washers where the nut contacts the toerail).

I “insulated” the flat plate of these replacement stanchion bases from
the toerail using multiple layers of heavy rubber self-amalgamating
tape and applied a coating of electrical insulating paste on top of
that before bolting them down. No problems eleven years later…

Granted, there’s less salt water “applied” to the sail track than the
toe rail, but why not use the best thing available? (Later) removal of
the Strong Track to re-fasten the underlying sail track down the road
won’t be an easy task.