good source for ss backing plates?

[campbdon]

I asked about G10 because I was concerned about using aluminum for backing plates (sheet or angle pieces) with SS fasteners. Should I be concerned or have others used Al and SS together without corrosion? Do you need to isolate them with paint or some seperator layer
Thanks again!

[markxengineerin]

There are many many locations where aluminum and stainless come together on most boats- just use Tefgel in the interface (or other form of isolation, but that's an easy one) and it will be good for a long long time.

[wingssail]

Originally Posted by campbdon

I asked about G10 because I was concerned about using aluminum for backing plates (sheet or angle pieces) with SS fasteners. Should I be concerned or have others used Al and SS together without corrosion? Do you need to isolate them with paint or some seperator layer
Thanks again!

Most of our backing plates are aluminum (some are starboard). All of our fasteners are SS.

Use tefgel or other form of isolation (I use locktite anti seize), keep them dry, and inspect them periodically. If corrosion appears, address it.

[mvweebles]

McMaster has a good selection of GPO3 fiberglass. Decent price. No need to glue or fiberglass. Buy thicker material and use it like aluminum plate. 3/8" thick is more tha. Enough. Easy-to-use.

McMaster-Carr Page:
https://www.mcmaster.com/electrical-...ss-gpo3-sheets

[Nepidae]

As to the last mention of using dissimilar metals, AL & SS, I think it is smarter to keep away from that.

Coating will wear or wick away and you have the potential of electrolysis.

Going with FRP, fiberglass sheets, you can use your SS fasteners with no dissimilar metal's issues.

Check out my post from McMaster/Carr for the FRP sheets.

Any questions, PM me.

[iansan5653]

I also use the "Structural FRP" from McMaster-Carr. For backing plate purposes, I think their FRP, G10, and GPO3 are all practically equivalent. The G10 is epoxy while the GRP and GPO3 are polyester.

I really like the FRP approach. It's much cheaper than aluminum, it's completely stable and impossible to corrode, and it's easy to work with. I can easily cut, drill, and sand it with handheld power tools. I don't glue it in.

We use to use G10 to build rocket bulkheads when I was in school - it's good stuff. ��

I would never use plywood (too soft). Starboard does probably work but it would have to be much thicker to achieve the same result.

I haven't done it yet, but lately I've been thinking about starting to include a 1/16" rubber interface between the backing plate and the deck (like this one: https://www.mcmaster.com/1290N33/ ). This flexible interface would, in theory, better distribute the loads by filling any irregularities in the surfaces, and it should eliminate the need to taper the plate by making the transition at the edges of the plate more gradual (not that I've ever done that anyway). And it would be much easier and less permanent than epoxy. Has anyone tried this?

[s/v Jedi]

Fiberglass backing plates are great. But I wouldn’t use GPO-3 because it is much weaker. I use it to mount electronics like dc-dc converters on.

If you can, I recommend to radius the corners and taper the edges. Using a router with 45 degree bit is great but even a file for metal or angle grinder works. When you taper the edge like that, you reduce the hard spot.

[campbdon]

Thanks for your advice! The area where it's installed isn't exposed to moisture other than rainfall or ambient humidity. Also the aluminum has much greater area/volume than the SS so I think that helps also. Think I'll stick with my plan and inspect regularly. But please keep any further advice coming if you have it!

[SteveSails]

If you can find a marina or dock installing a FG bulkhead you might be able to get all the backing plate material you need for no or little $. FG bulkheads are Z shaped interlocking panels of pulltruded FG about 1/4"thk and 10-12" wide, the cutoffs are useless to the dock builder so a dumpster dive or a small bribe should get you what you need. Cut the stuff with your favorite tools of destruction.