Aluminum and galvanized steel

[cavman138]

I recently bought a john boat and am going to put a deck on the front and back. While looking around for aluminum angle I found that I have some galvanized steel rails that were the tracks for some old garage doors. I feel like I have enough of it to make the decks, but I'm worried about corrosion. Would this just be an outright bad idea because I will be putting it in salt water some? Is there a way I can use the galvanized steel and prevent the possibility of corrosion?
Thanks

[Seahunter]

Mixing saltwater, galvanize and aluminum is a corrosion cocktail. Do yourself a favor and find some suitable aluminum for the project.

[BUDC]

Aside from the differing metals corrision problem above, I seriously question the ability of those rails to handle load from the top. The design is for load from inside on the U shaped bottom. Seems to me loading the top would only encourage them to fold and fail.
Any structural engineer-types know for sure?
In a salt water environment, I think you'd be lucky to get a year out of them.
Just my 2 cents, all opinion too!.
budc

[Clark W. Griswold]

Aside from the differing metals corrision problem above, I seriously question the ability of those rails to handle load from the top. The design is for load from inside on the U shaped bottom. Seems to me loading the top would only encourage them to fold and fail.
Any structural engineer-types know for sure?
In a salt water environment, I think you'd be lucky to get a year out of them.
Just my 2 cents, all opinion too!.
budc

If they are the overhead, sliding door rails like you typically find on a barn, they should handle the load fine. If they are the type that the door slides up toward the roof on, they won't be strong enough IMO.

I'd worry more about their durability in a salt water environment. Especially since they would be in contact with aluminum. I have had personal experience with galvanic corrosion on a truck where cast aluminum and steel were in direct contact. It could only be worse on a boat.

Take a look at this info on galvanic corrosion. Galvanic and Corrosion Compatibility Dissimilar Metal Corrosion - Engineers Edge

[cavman138]

I appreciate the input. I think I'm going to let this idea go. It just seemed like a great way to save some money and reuse some metal that's just laying around.
Thanks again

[lreops]

Aside from the corrosion, mixing different types of metals on a boat increases the effects of electrolysis and being that aluminum is softer than galvanized steel, the boat itself will be affected the most by being eaten away.

[Seahunter]

Aside from the corrosion, mixing different types of metals on a boat increases the effects of electrolysis and being that aluminum is softer than galvanized steel, the boat itself will be affected the most by being eaten away.

Has nothing to do with the hardness of the material.

Steel and aluminum are very close in nobility. The interaction between the steel and aluminum would be minimal to begin with.

In this scenario the zinc in the galvanizing would be the first to go. Once the galvanized coating was compromised the FE in the steel would start to oxidize (rust). The steel would fail of atmospheric corrosion long before the aluminum would be adversely affected by electrolysis.

[lreops]

Has nothing to do with the hardness of the material.

Steel and aluminum are very close in nobility. The interaction between the steel and aluminum would be minimal to begin with.

In this scenario the zinc in the galvanizing would be the first to go. Once the galvanized coating was compromised the FE in the steel would start to oxidize (rust). The steel would fail of atmospheric corrosion long before the aluminum would be adversely affected by electrolysis.

I stand corrected, for some reason my mind did not register the fact that galvanize was zinc, just for some reason focused on the steel part. Thanks for the correction.