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Hey Guys,

Marine welder here in Northern California is recommending hot-dip galvanized carbon steel for my stringer mounted motor mounts over 6068 aluminum. Any thoughts?

Thanks,

JohnV8r

John just had a pair made in straight steel then primed and painted...John N

I think you mean Aluminum Grade 6061 or Marine-grade 5000 series. Both are plenty strong and hold up to the marine environment, easy to work with. If left unfinished both will oxidize and start to corrode...but unless left damp next to wet wood or something that can take many years for substantial corrosion. If coated all the better.

Galvanized steel is strong and being galvanized will hold up to the marine environment. That is unless you scratch, drill, or grind away the galvanize. (zinc coating) actually, a little scratch kinda heals itself. I say this as I had to cut away some of my mounts to fit the exhaust...in aluminum, all I had to do was file the edges smooth. If it was galvanized, there is a cold spray that works ok...but really should be redipped. The only other issue is diesel fuel does not get along with the galvanized zinc coating. But if you don't get fuel on it and let it sit...not really a problem.


I don't think you can go wrong with either...if I was in that position, I'd go with what the person building prefers.

John,
I've used aluminum on engines up to and including Detroit Diesel 6 71 engines.

There is no reason to use galvanized steel over aluminum in your application at all.

Either the welder can't weld aluminum or he doesn't get how to design them and thinks they will be weak.

Thanks for the feedback guys!

Bruce-

Yes, Aluminum brackets done right are more than capable of doing the job, will be lighter and less prone to degrading due to corrosion.

Steel can also tackle the job and hot-dipped will hold up a good many years. Are there any benefits to using steel that I can see...not really, aside from that you could go a bit thinner on materials and steel is less prone to fatigue. But in this application that's not really a factor as they can easily be overbuilt using aluminum taking fatigue out of the equation.


I agree the fabricator may not have experience with Aluminum, may not have a welder capable of doing aluminum properly (both the machine and person) or they are just setup for steel, have experience with steel. If it were me I'd opt for steel if that was the shop I was going with. If I had a choice...and I did, I went with Aluminum as its an easier build, easier to modify, less prone to corrosion and I did not have to bring to a galvanizing place to have dipped. So for me, also cheaper. But either would have worked just fine.
If rust is an issue, which not really a problem with hot-dip, if coating is left intact...what does one do with the 2000lbs of iron the brackets are holding up.
Maybe something I'm missing.