Hi all,
I have bought some aluminium mooring cleats with holes threaded in the
underside to be fixed with bolts from under the deck. I know there are
isues with stainless and aluminium but as there should be no water
ingress to the threads is it ok to use stainless bolts? Or is there
still going to be corrosion.



It's just that I have a load in stock and I'd rather not go and buy a
load more in alloy!

On another issue, I have the fairleads to go with them, but these need
to be screwed with a wood screw from above into the beam shelf. I
don't see anybody selling alloy wood screws so I suppose its stainless
there. So (as salt water is going to be continually sprayed over them)
should there be some sort of protection (paste or plastic) between the
screw and the fitting?

Pete

Pete,
Your aluminium mooring cleats will be anodised, hope so anyway. This helps
resist corrosion. Where stainless steel fasteners or other parts are in
contact with aluminium parts the joints should be smeared with a zinc
chromate corrosion inhibiting paste such as Duralac. This is a bright yellow
paste, you can buy a tube from a chandler or from the internet for about
£10. If stainless steel fasteners fitted into aluminium are exposed to salt
water you will get corrosion of the aluminium to white corrosion product,
the inhibiting paste certainly helps to reduce this.

Allthough this combination of materials is not ideal, it is the best
practical solution for much hardware on sailing boats, obviously there are a
great many aluminium masts with stainless steel fittings attached and they
last a long time.

As for aluminium wood screws, they do exist, as you can tell from an
internet search, but as far as I am aware they are not something you can buy
from high street shops.

John



"pete" wrote in message
...
Hi all,
I have bought some aluminium mooring cleats with holes threaded in the
underside to be fixed with bolts from under the deck. I know there are
isues with stainless and aluminium but as there should be no water
ingress to the threads is it ok to use stainless bolts? Or is there
still going to be corrosion.



It's just that I have a load in stock and I'd rather not go and buy a
load more in alloy!

On another issue, I have the fairleads to go with them, but these need
to be screwed with a wood screw from above into the beam shelf. I
don't see anybody selling alloy wood screws so I suppose its stainless
there. So (as salt water is going to be continually sprayed over them)
should there be some sort of protection (paste or plastic) between the
screw and the fitting?

Pete

From my experience with stainless winch mounting screws into aluminium
mast, the major issue is getting them out if you ever have to. Last
time, I had to drill them out :-(

Pete,
The only serious issue with stainless in salt water is crevis corrosion and
as this is not under water, that problem is not severe. However the big risk
is electrolytic corrosion because of the dissililar metals. The solution is
to prevent moisture from migrating along the thread and becoming an
electrolite. To prevent that and allow easy extraction use an anti-sieze
compond found in auto supply stores. When using stainless wood screws to
fasten the fairleads, use a bedding compound around the screws and under the
base.
Steve

"pete" wrote in message
...
Hi all,
I have bought some aluminium mooring cleats with holes threaded in the
underside to be fixed with bolts from under the deck. I know there are
isues with stainless and aluminium but as there should be no water
ingress to the threads is it ok to use stainless bolts? Or is there
still going to be corrosion.



It's just that I have a load in stock and I'd rather not go and buy a
load more in alloy!

On another issue, I have the fairleads to go with them, but these need
to be screwed with a wood screw from above into the beam shelf. I
don't see anybody selling alloy wood screws so I suppose its stainless
there. So (as salt water is going to be continually sprayed over them)
should there be some sort of protection (paste or plastic) between the
screw and the fitting?

Pete

"Steve Lusardi" wrote in message
...
Pete,
The only serious issue with stainless in salt water is crevis corrosion
and as this is not under water, that problem is not severe. However the
big risk is electrolytic corrosion because of the dissililar metals. The
solution is to prevent moisture from migrating along the thread and
becoming an electrolite. To prevent that and allow easy extraction use an
anti-sieze compond found in auto supply stores. When using stainless wood
screws to fasten the fairleads, use a bedding compound around the screws
and under the base.
Steve

I like Tefgel http://www.tefgel.com/contain.php?param=tefgel_infor when
mixing metals. Common anti-seize is silicone and graphite powder and the
silicone will wash away.
MMC

On Sun, 6 Jul 2008 12:01:57 -0400, "mmc" wrote:


"Steve Lusardi" wrote in message
...
Pete,
The only serious issue with stainless in salt water is crevis corrosion
and as this is not under water, that problem is not severe. However the
big risk is electrolytic corrosion because of the dissililar metals. The
solution is to prevent moisture from migrating along the thread and
becoming an electrolite. To prevent that and allow easy extraction use an
anti-siedeze compond found in auto supply stores. When using stainless wood
screws to fasten the fairleads, use a bedding compound around the screws
and under the base.
Steve

I like http://www.tefgel.com/contain.php?param=tefgel_infor when
mixing metals. Common anti-seize is silicone and graphite powder and the
silicone will wash away.

The discussion was deck cleats,fastened with capscrews from below. If
the antiseize is washing away, then Davy Jones Boatyard is doing the
work. Use a bedding compound under the cleats.

Casady

Thanks guys, i know what to do now
Pete

"Richard Casady" wrote in message
...
On Sun, 6 Jul 2008 12:01:57 -0400, "mmc" wrote:


"Steve Lusardi" wrote in message
...
Pete,
The only serious issue with stainless in salt water is crevis corrosion
and as this is not under water, that problem is not severe. However the
big risk is electrolytic corrosion because of the dissililar metals. The
solution is to prevent moisture from migrating along the thread and
becoming an electrolite. To prevent that and allow easy extraction use
an
anti-siedeze compond found in auto supply stores. When using stainless
wood
screws to fasten the fairleads, use a bedding compound around the screws
and under the base.
Steve

I like http://www.tefgel.com/contain.php?param=tefgel_infor when
mixing metals. Common anti-seize is silicone and graphite powder and the
silicone will wash away.

The discussion was deck cleats,fastened with capscrews from below. If
the antiseize is washing away, then Davy Jones Boatyard is doing the
work. Use a bedding compound under the cleats.

Casady
You must have missed the part about galvanic action between s/s and
aluminum. I think all agree about the bedding compound.

On Tue, 8 Jul 2008 11:11:58 -0400, "mmc" wrote:

You must have missed the part about galvanic action between s/s and
aluminum. I think all agree about the bedding compound.

Aluminum needs to be nearly twice as thick to have equal strength. The
boltholes ain't that big. You use antiseize amd hope for the best.
Aluminum bolts and screws are scarce, which may actually be the
deciding factor. You know a source for aluminum fastners ? The high
strength alloys, of course.

Casady

"Richard Casady" wrote in message
.. .
On Tue, 8 Jul 2008 11:11:58 -0400, "mmc" wrote:

You must have missed the part about galvanic action between s/s and
aluminum. I think all agree about the bedding compound.

Aluminum needs to be nearly twice as thick to have equal strength. The
boltholes ain't that big. You use antiseize amd hope for the best.
Aluminum bolts and screws are scarce, which may actually be the
deciding factor. You know a source for aluminum fastners ? The high
strength alloys, of course.

Casady

Nope. Right now I'm in the process of rebuilding my 1997 pontoon boat and
would have liked to use aluminum machine screws instead of stainless. Unlike
the manufacturer, at least I'm not using s/s screws and metal nuts!