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