Galvanized bolts ok for aluminum?

I know, I should go with S/S but for the amount of bolts I need, the $$$ starts adding up.

Will galvanized bolts/nuts/washers be ok?, will they rust out first over the aluminum?

I say no, the galvanized bolts that the po had on my boat really caused some damage. SS is the way to go.

I agree with BW, galv will rust and corrode your aluminum... and eventually eat some nice holes in it.

Stainless is worth every penny.

jigngrub said:

I agree with BW, galv will rust and corrode your aluminum... and eventually eat some nice holes in it.

Stainless is worth every penny.

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+2

Or aluminum . . .

Menard's has bulk bags of SS hardware at good prices. Buy the longest your going to need and cut them down for where you need shorter bolts.

https://www.fastenersuperstore.com/searchResults/stainless-machine-phillips-pan

Buy in bulk - a thousand?

+78627 for SS

I buy my stainless from Fastenal and Lowes.

Any metal used in a marine application needs to be made of stainless, aluminum, or bronze. No ifs ands or buts about it.

Pay the price now in money, or, cut corners, and pay the price later down the road with issues such as galvanic corrosion/electrolysis, and trust me, that costs you a LOT more than what you would spend in fasteners.

Somehow I had used 4 galvanized nuts/bolts/washers in the transom and this past summer, replaced them with S/S.

There are different alloys of stainless steel. IIRC you want 316.

You should check out these company's I have bought from both of them.
The one has free shipping too. Both I would order from again.
https://www.fastenerusa.com/
https://www.fmwfasteners.com/

Stainless steel is steel with nickle in it. Add it to aluminum and you have a electrolysis with water added. My transducer bracket was SS and ate that size hole through the stern. Every place I used SS corroded the aluminum it came in contact with. I use my boat almost always in salt water but fresh will do it too. With galvanized steel it is coated with zinc, the zinc will disappear first from electrolysis then you are left with the steel.

There are tables showing what metals will create the highest corrosion from electrolysis. That is where to start.

Separation of the materials from each other only makes c more active. Mechanical bonding of the materials can help stop electrolysis but the materials must be sealed against air and moisture intrusion.

xbacksideslider said:

https://www.fastenersuperstore.com/searchResults/stainless-machine-phillips-pan

Buy in bulk - a thousand?

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No. You can buy them one at a time or in bags of maybe 10 or 25 or some other multiple. Much cheaper in bulk and there's always some use for them. As already said, much cheaper to buy SS now than deal with the problems later.

Al u minum is technically correct.

The charts will show that galvanized will actually react a little less than SS.

The difference is pretty negligible. But it's there.

For those who say galvanized will corrode your boat, I offer this:



A 50 year old boat. With galvanized seat brackets in direct contact with the aluminum hull. Fastened to that hull with aluminum rivets.

Edit to correct: these brackets are aluminum. My bad. I swore I saw sparks when grinding them off. After Johnny pm'd me I double checked. They're ALUMINUM! [emoji33] Oops!

And, just for fun... Did you know that wooden boatrights will almost NEVER use SS fasteners below the waterline, or in a boat to be fiberglassed over?

Why?

Because stainless steel requires the presence of air to remain "stainless."

oakchas said:

And, just for fun... Did you know that wooden boatrights will almost NEVER use SS fasteners below the waterline, or in a boat to be fiberglassed over?

Why? Because stainless steel requires the presence of air to remain "stainless."

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True. But what you're actually referring to is called "crevice corrosion" and that layer of air provides the insulation (if you will) that allows the SS to protect itself. 316 is the better SS series in that regard, but fugghedabout that for now.

Whenever SS is cut off from the oxide layer, it will corrode. Take a look of that photo of a SS bolt I pulled out of my transom swim platform that had only been installed for a few years! Not only is part of the body in the middle of the bolt "missing" but look where the threads to the left are deteriorating too.

FWIW ... here's some info I had posted on my Parker boat website regarding stainless steels that might help some:

Looking specifically at stainless steels, one can also quickly see why SS is great choice out of the water … but not the best choice for a mariner whenever it is fully immersed in water. And most SS hardware for the marine market is the 304 or equivalent series. (Note, SS can also be passivated, which adds protection, but I didn't want to bore you with too much details, but simply put ... passivation provides an extra measure of resistance and good corrosion resistance in stressful situations (salt spray, chloride contact, etc.) due to the chromium enrichment of the surface.).

* Galvanic corrosion is corrosion that naturally occurs between dissimilar metals. Put a SS fastener in a tin boat and the aluminum boat surrounding the SS fastener or hardware will be eaten away in time.

* Such corrosion is exacerbated in the presence of an electrolyte (water) and even worse, when coupled with a chloride (salt from saltwater). Now you know ?why? saltwater can be sooooooo corrosive. Further evidence of this that you may have seen for yourself is older aluminum spinning reels where the paint was flaking off around the SS screws. The aluminum housing under the paint was corroding within itself, and where the paint flaked off, you may have seen a white powered corrosion (salt).

* Stainless steel is not truly stainless. The high chromium and/or nickel content makes it stain‘less’, but no SS alloy is truly stainless.

* What causes SS to lose it’s protection? SS gets the layer of protection from the oxygen in the air, and/or it's passivated surface. Eliminate it - like immersing it in water, or allowing water to sit on the material, or completely encapsulating the SS fastener in an enclosed hole – and the SS will corrode. An example of this is when you see ‘rust’ forming on the tops of the SS screws used to hold SS cleats or SS rod holders onto the f’glass washboards.

* ‘Working’ SS (machined, punched, drilled, or welded) can remove the protective oxide layer. The heat or mechanical action can disrupt the atoms at the surface and remove the protective oxide layer, leaving the area worked pretty close to be plain carbon steel. This is why Lenco trim tabs can rust and fall off – happening to more than one I know of in its 1st year of use (as the rolled hinge area is also welded).

* SS is also prone to crevice corrosion when under heavy tensile loads. That is why those ‘cheap’ SS hose clamps look so darn rusty! It is under a load and the band was pierced by a heavy metal punch machine. I recommend full-band-type of hose clamps, known as AWAB brand clamps, for any critical below-the-waterline internal connections. I've seen SS bolts holding deck hardware on that were reduced to 1/2 their full diameter, in the middle of the bolt, because the SS was fully enclosed inside the boat structure, which cuts off the oxide protective layer.

* If you need to put SS through aluminum – insulate them. They make special lubricants or protective ‘goops’ for this (Tef-Gel is but one brand), but I use adhesive-line heatshrink on the fastener body and thick nylon washers under the bolt head and nylok nuts.

Thanks for elaborating! I love learning new stuff.

The PO of my boat used green treated lumber and galvanized lags to hold it down. I got lucky. The green lumber (treated with copper) had not yet attacked the boat hull.

And, the screws holding the fixtures down on my boat were probably chrome plated at one time. Oar locks, nose piece, transom corners. The screws were all there, but a bit rusted.

The galvanized lags I mentioned before were in similar condition. Most of those had gotten wet at some time but all in all, in good shape.

As for me, I'll probably use SS for trim, but elsewhere, for structure that may see much fresh water, I'll stick with galvanized.

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I just mounted a kicker board to my boat. But the local hardware store did not have 4 1/2" bolts. So, I got grade 5 yellow chromed bolts instead. I did get Stainless washers and nuts. I was wondering that when I remount the board after painting it if I coated the shaft of the bolts would that protect it from making contact with the aluminum.

Sincerely,

jbird68

Hmmmm so what is the solution? I am in the process of replacing the transom wood in my tinnie and have bought SS bolts, SS nylon lock nuts, and SS fender washers to bolt the new wood back on. The bolts that were there had corroded in only a few years, but I don't think they were SS.

I'm planning on using stainless steel hardware for the construction of my deck. Would it be safe to use SS galvanized "L" brackets? They will be exposed to both the aluminum deck hull (screwed into ribs for deck support) and the SS hardware itself.