All this talk of leaking toons got me paranoid and..........

[badmoonrising]

Aluminum will corrode when exposed to stainless in a salt environement.

BMR, I think you've just been very fortunate or your Stainless is not in direct contact with the aluminum..

I'm just saying from experience restoring boats (my third aluminum boat) that every piece of hardware that was brass caused severe corrosion, especially to my Starcraft's hull. The previous owner mounted a lot of stuff with brass, every contact point was severely pitted. The brass hardware he used to mount the transducer caused a 3 inch hole in the transom. All stainless hardware on every boat is direct contact. I've never seen stainless react with aluminum, ever. I guess I was very fortunate to have it occur on all 3 of my aluminum boats

Every manufacturer out there uses all stainless and aluminum hardware and It's not a problem. I would think boat manufacturers have done enough research that they all think stainless is ok. The only brass hardware I've ever seen on new boats is the rare brass drain plug. We get a season or 2 out of them up here.

[GregF]

Have you ever looked closely at the washers used on the lower unit? The ones on the bearing carrier studs and the center stud under the cavitation plate are brass ... just sayin'.
I agree I thought it was a problem, that is why I asked Mercury before I screwed a brass water temp sensor in the block. If anything heat speeds up chemical reactions and I saw where the Evinrude water temp sensor rotted a huge hole out of the manifold. I do agree it is probably an aluminum alloy problem.
In the case of the stainless situation. I have some places that had no problem and others with a hole the size of your finger. Same bolts, different aluminum.

[cbavier]

So probably what (I/we) think is Brass drain plugs really isn't brass at all, but some other metal. I do know the threads are tapered. When I have my tubes leak checked in the spring. I'll ask the welding shop. They will know because they are a big commercial outfit.

[JohnO]

Aluminum will corrode when exposed to stainless in a salt environement.

BMR, I think you've just been very fortunate or your Stainless is not in direct contact with the aluminum..

I'm just saying from experience restoring boats (my third aluminum boat) that every piece of hardware that was brass caused severe corrosion, especially to my Starcraft's hull. .... All stainless hardware on every boat is direct contact. I've never seen stainless react with aluminum, ever. I guess I was very fortunate to have it occur on all 3 of my aluminum boats

I'm just saying what the science says. Stainless reacts with Aluminum (galvanic couple). Are your contact points painted? Heavily oxidized? Anodized aluminum and passivated Stainless. All these things will decrease corrosion.

[GregF]

The guys around here who make bimini tops use TefGel wherever stainless and aluminum connect. That seems to make it better. The antiseize we use is to prevent this problem too. It puts a coating between the aluminum threads and the stainless bolts. Without it, your bolts are likely to come out with the aluminum threads still attached ... as a white powder.

[badmoonrising]

Have you ever looked closely at the washers used on the lower unit? The ones on the bearing carrier studs and the center stud under the cavitation plate are brass ... just sayin'.

Not on any Mercruiser outdrive I've ever worked on, and I've worked on a ton of them. No brass anywhere. Everything is stainless.

I agree I thought it was a problem, that is why I asked Mercury before I screwed a brass water temp sensor in the block.

The block's not usually submerged Put brass in contact with aluminum and submerge that peice in saltwater and teh aluminum is destroyed. Quickly.

In the case of the stainless situation. I have some places that had no problem and others with a hole the size of your finger. Same bolts, different aluminum.

If you are referring to your snaps again, they are chrome plated brass...proving my point that brass and aluminum don't mix. This is where black streaks come from...dissimilar metals cause those near impossible to remove streaks. Install 100 stainless snaps (i.e. with stainless screws) and black streaks do not occur. Good quality stainless is non reactive.

[badmoonrising]

I'm just saying what the science says. Stainless reacts with Aluminum (galvanic couple). Are your contact points painted? Heavily oxidized? Anodized aluminum and passivated Stainless. All these things will decrease corrosion.

And I'm saying what I've observed owning/restoring aluminum boats that spent their entire lives in a brackish environment. I've been boating since I was 14 and all but one vessel I've owned was aluminum from jon boats to my pontoon and I've never seen stainless cause any problem when in direct contact with aluminum. All of my boats were bare aluminum with the exception of my pontoon. None were heavily oxidized, rather the opposite...even my '58 Alumacraft had zero issue with it's factory installed stainless hardware. The '68 Starcraft only had issues where brass was used and no problems where stainless was used.

Now there is chinese made low quality stainless, which is crap and will cause problems. That's why I bring a magnet with me when I buy stainless hardware. Every boat builder out there gives this advice. Even some "stainless" hose clamps have steel screws.

[GregF]

Not on any Mercruiser outdrive I've ever worked on, and I've worked on a ton of them. No brass anywhere. Everything is stainless.

I always thought so too until I scratched the zinc plating off of one of them. It is yellow metal, not stainless.

I will have my boat out of the water an a couple weeks I will get a picture of one.

[badmoonrising]

Not on any Mercruiser outdrive I've ever worked on, and I've worked on a ton of them. No brass anywhere. Everything is stainless.

I always thought so too until I scratched the zinc plating off of one of them. It is yellow metal, not stainless.

I will have my boat out of the water an a couple weeks I will get a picture of one.

Every piece of hardware on both Merc. drives I own and everyone I've ever encountered is all stainless. I buy hardware from Merc dealer all the time and the only non stainless hardware is sensors and teflon composite drain gaskets.

Also never seen any boat hull with anything but: chrome plated Zamac (corrodes the hell out of aluminum hulls), aluminum or stainless. Snaps are chrome plated brass...that's it. Try and find 100 percent stainless snaps and I'll buy them. It'll do away with black streaks.

If anyone can show me brass hardware factory installed on their boats, then please do post pics.

Better yet, this summer I'll place a piece of aluminum in the water with: a brass bolt/nut. Another peice with a stainless bolt/nut...and take wagers one what gets destroyed and what doesn't. Nothing like a real word test.

I already know nothing will happen withe the stainless because our floating docks are aluminum with stainless hardware. 5 5 seasons and zero corrosion issues.

Now add in stray electric current and you have a different outcome. In that case, the aluminum becomes the anode and is destroyed.

[GregF]

This is from a can of bolts I took out when I was working on my boat.

What do you figure the white stuff is on these SS bolts?(came out of aluminum and that square piece is aluminum). I guarantee if I knock this out of square washer there will be a ragged hole where the clean drilled hole used to be.
If this was actually threaded into the aluminum it would just come out in a puff of white dust and there would be no threads left in the aluminum.

[lakerunner]

Looks like old caulking

[GregF]

Yup until you touch it. This is a fine powder you can crumble with your fingernail.
I know it is not caulk because I put the bolt in and I didn't caulk it.

[badmoonrising]

Looks like corroded aluminum that was unpainted and exposed to salt. If the bolts were removed and the aluminum was not repainted when the paint was damaged, sure that will occur. Any tech manual tells you that all exposed aluminum on lower units is to be painted if damaged. If you did the same thing without the ss bolts being in it, the same corrosion would happen.

Use steel or brass and it would be much worse.

Good quality stainless is non reactive unless you factor in stray electrical current or the wrong type of antifouling paint applied to an aluminum hull (i.e copper paint, a no no on aluminum). Poor quality stainless is reactive. That's why when I buy ss hardware I bring a magnet with me, it was the advise of a local boat builder. He wrote an article once in our local boating mag "The Mariner" where he would got to Home Depot and alot of the stainless they sold would attract a magnet.

If the stainless is of good quality and you add in stray electrical current (lots of marinas have this problem, especially home built slips where electrical code wasn't followed) of course the aluminum will be sacrificed while the stainless remains intact because the aluminum becomes the anode. Especially if the factory installed anodes on the motor are depleted, the wrong type for the application (there are fresh and saltwater anodes).

You already posted pics of severe corrosion happening on your chrome plated brass snaps, which pretty much proves my point.

[GregF]

Now you have me confused. Are you saying if I put a stainless plug in my pontoon I have to paint it? (the treads?)
I agree this is aluminum corrosion but it is where it is in contact with the stainless.

As for the magnet, 304 stainless, the stronger alloy, is magnetic. Try your prop. OTOH 316 is more reactive with aluminum than 304, look at the reactivity chart.

In the mean time I will stay with my plastic plugs, like the manufacturer used.

[badmoonrising]

Threaded plugs with thread compound or gaskets prevent the aluminum from coming in contact with water. Anything exposed to water needs to be painted.

A bolt, nut and washer does not. Common sense.


My prop is not magnetic. Nor is any ss hardware I've ever bought or is currently installed on my boats or outdrives. And I've had lots of them.


I can post pics I you like. I also have no corrosion on any of the ss hardware on my out drives and one boat is 11 years old, the second is 5. Also, can post pics. I maintain everything, every scratch gets painted every season, it's all about taking proper care of what you have.