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The Panamanians didnt give a stuff about cruising boats
Sounds like me :)

I do however have an interest in Aluminum boats. I spent maybe about 7 years working on aluminum work boats 45-70 ft, mostly salvage and fishing vessels. Folks know why they make modern working boats out of aluminum right? Because it can take more punishment than fibreglass. It does however, also require more skill to maintenan and is trickier to repair and is more expensive.

I have seen my share of damage, and been there for my share of repairs, in some fairly bare bones yards. It doesnt take a highly specialised ship yard to make a repair. If a ship yard is repairing cruise ships, tankers, local ferries, they should the equipment and the tradesmen to handle a small aluminum plating job.

The German marina thing is weird, I didnt watch that video. Its possible that the professional yard was simply too expensive for her. If she has a repair budget of $8000, like some one said, thats not going to go far. A repair budget that size could have caught up on her on a fibreglass boat too.
 

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I'd expect she was seeking advice from German yards for two reasons. One being that metal boats are more often built by yards in the EU. The other being that when you are dealing with something technical that may be beyond your expertise, it helps to discuss things in your native language. Eliminates translation errors and provides nuances that non-native speakers often simply will miss.

For instance, Indians educated under the culture of the old UK Colonial schooling in modern day India, will often be saying "Yes yes" while having a conversation. To an American, that means they are agreeing with what we are saying. To an Indian...it just means "I hear you". There are cultural differences that can often really screw up a critical technical discussion, so it is not surprising that she would make the phone call or email (given that the cost of doing that locally or globally is the same) to someone who speaks her native language. And, might have better technical skills, yes.
 

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Its a reality thing for her and about her...with karl as the base.
Makes sense.
Friendly support was more available on the other side. Easier to float and fart around there so are more like minded adventurers.
Soutth side is more serious...leapers.
Glad shes still at it and will see how this plays out.
Best wishes and all that....
 

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Discussion Starter #125
The most recent video #20 showed a few interesting things: she scrapped the fuel tank and replaced it with a (looks like) custom made rotomoulded tank professionally made. Looks good.

The holes and porous hull are from the old SS tank home built to the aluminium hull with only some epoxy as a barrier between... As soon as water enters the bilge it takes only a pin hole in that epoxy for the electrolysis to hit the hull... And 30 years for it to do it.

In #19 you can see the extent of damage in the fuel tank bay... But you xant see the surrounding area.

I wonder how far that sort of electrolysis could affect the surrounding aluminium?

If it's just the local area plating would seem obvious and 'affordable'.
 

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....I wonder how far that sort of electrolysis could affect the surrounding aluminium? .
Stainless steel is further up the noble list than straight steel and aluminum is further down than both of them. Aluminum should be the anode to either and become the sacrificial metal.
 

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How far?

Or the whole outer surface of the hull?
Both mild steel and stainless steel are plenty far enough apart on the galvanic table to allow for reaction. Stainless being much further apart from aluminum, than mild steel. Meaning, the galvanic potential for stainless vs aluminum is much greater.

I'm not sure if the entire hull would be exposed or only the part connected by water (electrolyte) to the dissimilar metal. My guess is it's theoretically the entire hull, but the potential is greatest for the area exposed to the electrolyte.
 

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SS tank in a aluminum boat is trouble. When I bought my 33’er it had these beautiful custom SS water tanks own in the keel. The PO, a really wonderful guy, was soooo proud of them. I pulled them out. Converted the space to storage, latter converted them to fuel tankage. Best way I know to protect the steel is to immerse it in diesel.

On my two steel boats I’ve seen numerous instances where some piece of SS is close to a bit of mild steel and the mild steel world corroded, anywhere from a 1/2” to 1-1/2” away. The last was a bit of SS on a wooden hatch, had a hole nearly through the deck. Small hole I welded back up in an hour.

The corrosion occurs when the dissimilar metals are close but not electrically bound, they try to equalize the potential by electron transfer. (god I hope I’m saying that right!) When you weld SS and mild steel there is a very low potential path between them, this ends the corrosion. Unfortunately you can’t weld aluminum to just about anything else, so corrosion. Even between aluminum alloys, I’m fighting an issue with my Aries wind vane over this now, despite tons of anticorrosive.

My guess is that the corrosion would be local to the tank. If the reaction is being satisfied locally then there is less potential for it to go a long distance.

It would have been more cost effective to have the welding done and make the void the tank. Save the cost of the new tank and the space becomes a de facto double bottom.
 

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The most recent video #20 showed a few interesting things: she scrapped the fuel tank and replaced it with a (looks like) custom made rotomoulded tank professionally made. Looks good.
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Those rotomoulded tanks were water tanks she was removing so her Austrian boat building friend could inspect more of the hull while the boat was in the water.
 

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....When you weld SS and mild steel there is a very low potential path between them, this ends the corrosion...

I've not heard this before and am trying to make sense of it. I can imagine, when two metals are welded, there is no way for an electrolyte to get between them, at the weld, and create a pathway for the galvanic action. However, if you submerged the entire welded item in an electrolyte, I don't see how the weld would prevent galvanic reaction any more than two metals that are bolted together.

I'm currently dealing with the classic galvanic pita on all boats. Stainless steel machine screws, into aluminum. I'm trying to get the aft boom end off and half the screws are too corroded to get them to back out. This only from 14 years of rain water soaking them occasionally.
 

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...When you weld SS and mild steel there is a very low potential path between them, this ends the corrosion...
I'm not sure this is a correct statement. My understanding of the galvanic corrosion process is as follows: The ion exchange occurs at the interface between the metals and the electrolyte, seawater in this case. For this process to proceed, the metals have to be able to transfer electrons as well, which can only happen if the metals are physically connected by a conductor. If the metals are welded, that path is a very low resistance path making the electron transfer that much easier. If electron transfer is easy, the galvanic reaction can proceed. Galvanic corrosion is a real concern for welds. Depending on what metals are involved, it is also possible to generate hydrogen, which can lead to hydrogen embrittlement, a much worse failure mechanism than corrosion.
 

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I've not heard this before and am trying to make sense of it. I can imagine, when two metals are welded, there is no way for an electrolyte to get between them, at the weld, and create a pathway for the galvanic action. However, if you submerged the entire welded item in an electrolyte, I don't see how the weld would prevent galvanic reaction any more than two metals that are bolted together.
No need for immersion. A single drop of water across the weld to both metals completes the galvanic path.
 

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Not arguing that if you immerse it in electrolyte you will have a problem. I’m talking about in “dry” locations. And no location on a boat is truly dry. But in any case, above water line applications.

I’m not sufficiently well versed to argue the matter out. I’m simply reporting what I observe all too often in practical application.

In this particular case I’m supporting the idea that a SS tank in an Aluminum keel is a bad idea.

I’m also reporting I observe corrosion where two materials come close together.

I may be wrong in my approach to a fix. When you say in “certain metals” you cause embrittlement, which metals? And what is the rate of degradation? If it’s 50 years I don’t care as long as it stops or slows rust.

P.S. I just did a quick internet search and it seems that welding 316 to mild steel is a very common practice with no special warnings, including on boats.
 

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All this discussion reinforces my view that you really need to know what you’re doing to own a metal boat, and most especially an Al one. Or indeed a wood-hull boat.

In one of the linked videos I was really struck by how little research or thought our protaganist did before deciding that she must have a metal boat. I’m all for frugal cruising, but one basic lesson of this life is that you gotta do your research before making big decisions. I was pretty unimpressed with her explanation of “why this boat.”
 

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Not arguing that if you immerse it in electrolyte you will have a problem. I’m talking about in “dry” locations. And no location on a boat is truly dry. But in any case, above water line applications.

I’m not sufficiently well versed to argue the matter out. I’m simply reporting what I observe all too often in practical application.

In this particular case I’m supporting the idea that a SS tank in an Aluminum keel is a bad idea.

I’m also reporting I observe corrosion where two materials come close together.

I may be wrong in my approach to a fix. When you say in “certain metals” you cause embrittlement, which metals? And what is the rate of degradation? If it’s 50 years I don’t care as long as it stops or slows rust.

P.S. I just did a quick internet search and it seems that welding 316 to mild steel is a very common practice with no special warnings, including on boats.
As a Certified Marine Corrosion Analyst I'd suggest you don't believe everything you read on the internet.
 

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All this discussion reinforces my view that you really need to know what you’re doing to own a metal boat, and most especially an Al one.
Absolutely correct. Aluminum boats can be destroyed in a mattter of days by amateur electricians.
 

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....I’m talking about in “dry” locations. And no location on a boat is truly dry. But in any case, above water line applications.....
If you really meant dry, then sure, no corrosion at the weld. You need an electrolyte, not simply touching metals.

It's very common to have stainless steel parts in contact with aluminum masts. They are intermittently exposed to an electrolyte (rain or spray) and still corrode. Albeit very slowly. I will be treating the screws I'm trying to remove right now with TefGel, before they go back in.
 
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