Hi all,

I want to put on backing plates for all the stuff attached to the transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through the
glass! I am really new to all this but the first thing that comes to mind is
reaction between two metals. If I use stainless bolts, could I use aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve

Steve;
I would look into the reason you have too keep "snugging them", and
there's reason to look at the burried nuts. Sounds like a plywood core
that's rotten.

Backing plates won't help if the center is soft.

Jim

sel1 wrote:
Hi all,

I want to put on backing plates for all the stuff attached to the transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through the
glass! I am really new to all this but the first thing that comes to mind is
reaction between two metals. If I use stainless bolts, could I use aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve

On Sun, 12 Dec 2004 03:54:43 +0000, Jim wrote:

[moved top-post down below OP]

sel1 wrote:
Hi all,

I want to put on backing plates for all the stuff attached to the transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through the
glass! I am really new to all this but the first thing that comes to mind is
reaction between two metals. If I use stainless bolts, could I use aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve



Steve;
I would look into the reason you have too keep "snugging them", and
there's reason to look at the burried nuts. Sounds like a plywood core
that's rotten.

Backing plates won't help if the center is soft.

Jim


This is good advice. But to answer one of the original questions, I
don't think there is any problem with corrosion between aluminum
backing plates and stainless hardware. For one thing, you will be
putting some kind of sealant in the hole, and this sealant will
probably end up mostly insulating the aluminum from the stainless.
And for another thing, it will take a long time (20 years?) for there to
be enough corrosion on a 0.125" backing plate to worry about.

--Mac

On Sun, 12 Dec 2004 03:54:43 GMT, Jim vaguely
proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email



I would look into the reason you have too keep "snugging them", and
there's reason to look at the burried nuts. Sounds like a plywood core
that's rotten.

Or maybe a bad design that has a foam core with not even "pads"
between the glass where there are pressure plates.

Backing plates won't help if the center is soft.

Which can apply with foam. Same problem occurs. It's best to have
solid "pads" at pressure points, even with backing plates on top.
---
Only worry about the things you can control.

Then you have stuff all to worry about!

sel1 wrote:
Hi all,

I want to put on backing plates for all the stuff attached to the transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through the
glass! I am really new to all this but the first thing that comes to mind is
reaction between two metals. If I use stainless bolts, could I use aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve


Backing plates are good, so long as any nearby core material is
sealed from moisture ingress with solid pads of epoxy around the
bolt holes. There is nothing more destructive over time than water
and freezing temperature cycles.

There will be very little galvanic action if the metals are not wet
with salt water much the time. If they are out of the weather, they
will be stucturally fine, especially if they are protected by a good
dose of bedding compound, or a coat of primer, paint or wax.

While I believe aluminium backing plates would be OK, if I was going
to do it from scratch, I would use SS plates, just on spec.

Anywhere that does sheet metal will have lots of scraps that will do
the job, and the only drawback to SS backing plates is that they are
harder to drill by far than is aluminium.

At sea, in general, it is always best to use the same metals if they
are going to be wet and in electrical contact.

Terry K

Top posting versus bottom posting, let me explain, scroll down:

Old Nick wrote:
On Sun, 12 Dec 2004 03:54:43 GMT, Jim vaguely
proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email




I would look into the reason you have too keep "snugging them", and
there's reason to look at the burried nuts. Sounds like a plywood core
that's rotten.


Or maybe a bad design that has a foam core with not even "pads"
between the glass where there are pressure plates.


Backing plates won't help if the center is soft.


Which can apply with foam. Same problem occurs. It's best to have
solid "pads" at pressure points, even with backing plates on top.
---
Only worry about the things you can control.

Then you have stuff all to worry about!

There, see? You has to scroll down to read what you could have read
without moving your cursor and scrolling.

I don't know why you said "vaguely
proposed a theory . . ."

Saying to check the reason for the loose bolts isn't exactly vague. I
know about how today's powerboats are made, and I'll bet he's got some
rot in a piece of structural plywood.

If that's the case, backing plates will not fix it.
Jim

On Sun, 12 Dec 2004 18:10:49 GMT, Jim vaguely
proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Top posting versus bottom posting, let me explain, scroll down:

Old Nick wrote:
On Sun, 12 Dec 2004 03:54:43 GMT, Jim vaguely
proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email




I would look into the reason you have too keep "snugging them", and
there's reason to look at the burried nuts. Sounds like a plywood core
that's rotten.


Or maybe a bad design that has a foam core with not even "pads"
between the glass where there are pressure plates.


Backing plates won't help if the center is soft.


Which can apply with foam. Same problem occurs. It's best to have
solid "pads" at pressure points, even with backing plates on top.
---
Only worry about the things you can control.

Then you have stuff all to worry about!

There, see? You has to scroll down to read what you could have read
without moving your cursor and scrolling.

So are you arguing for top or bottome posting?

If you had top posted and I had half a brain and had followed the
thread, I could have read your reply without having to scroll. And if
you had trested the post _correctly_ and removed half the crap from
previous posts before you started your bitching, then I would not have
had to scroll.


I don't know why you said "vaguely
proposed a theory . . ."


You tell me how to run the Web, then take exception to a stock joke
headline?


Saying to check the reason for the loose bolts isn't exactly vague. I
know about how today's powerboats are made, and I'll bet he's got some
rot in a piece of structural plywood.

If that's the case, backing plates will not fix it.

No. And I agreed. Sheeeeesh! Bad hair day guy!
---
Only worry about the things you can control.

Then you have stuff all to worry about!

On Sun, 12 Dec 2004 18:10:49 GMT, Jim vaguely
proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

_Partial_ understanding of your post. I did not bottom post. You
should not have had to scroll to read what I had to say. If you did
them sort out your news reader. I extracted what I thought was cogent
and interleaved my comments. I do this sometimes, and top post mostly,
also often removing a lot of the previous material.

I believe that bottom posting is the "correct" way anyway, although I
disagree with it.

In the end if it's done with a bit of thought it all works. Even if it
doesn't work..let it go!

Top posting versus bottom posting, let me explain, scroll down:

---
Only worry about the things you can control.

Then you have stuff all to worry about!

Some people hate top posting. I appreciate it when I don't have to
scroll through a bunch of stuff I've already read.

Don't know why they want the reply at the bottom.

But, we were talking about backing plates. . .

I would make sure the core is very dry and refurbished in some way before
any stuff is applied to build up and bed the breaches in the hull.
Also different metals in contact in a moist (air) environment, are not the
best way to go if you can avoid it. I have a steel boat which is happier
with the zincs attached when sitting on its cradle in damp weather.
Ask a surveyor who knows steel boats and they will tell you that the humid
environment is still going to foster some galvanic action. If your happy
with thick plates of a different metal that is your call but you maybe in
for a bit of a surprise in the area of under-film corrosion if there is any
contact between the metals via the fastening hardware on your glass boat.
I have done a bit of corrosion testing with coatings on metals in a lab
setting and it is quite impressive to see how insidious nature is when it
comes to metals having a "desire" to oxidize in most environments--even
before they are coupled.
Good luck,
Leo

"Terry Spragg" wrote in message
...
sel1 wrote:
Hi all,

I want to put on backing plates for all the stuff attached to the
transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through
the
glass! I am really new to all this but the first thing that comes to
mind is
reaction between two metals. If I use stainless bolts, could I use
aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve


Backing plates are good, so long as any nearby core material is
sealed from moisture ingress with solid pads of epoxy around the
bolt holes. There is nothing more destructive over time than water
and freezing temperature cycles.

There will be very little galvanic action if the metals are not wet
with salt water much the time. If they are out of the weather, they
will be stucturally fine, especially if they are protected by a good
dose of bedding compound, or a coat of primer, paint or wax.

While I believe aluminium backing plates would be OK, if I was going
to do it from scratch, I would use SS plates, just on spec.

Anywhere that does sheet metal will have lots of scraps that will do
the job, and the only drawback to SS backing plates is that they are
harder to drill by far than is aluminium.

At sea, in general, it is always best to use the same metals if they
are going to be wet and in electrical contact.

Terry K