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