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Foil galvanic corrosion
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neilsather



Joined: 20 Jun 2002
Posts: 14

PostPosted: Wed Aug 28, 2019 1:02 am    Post subject: Foil galvanic corrosion Reply with quote

It is not just the screws on the foils that will corrode. The aluminum fuselage within the front wing will start a galvanic corrosion with the carbon fiber. Any water left in the wing acts as an electrolyte and both the carbon and the aluminum will begin to corrode. If you leave the parts together for even a short amount of time you may not be able to remove the front wing. The aluminum
creates a thick paste and the carbon begins to fall apart, they will not want to separate.
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isobars



Joined: 12 Dec 1999
Posts: 20865

PostPosted: Wed Aug 28, 2019 12:39 pm    Post subject: Reply with quote

I knew about the corrosion threat with all the bolts/screws, but hadn't thought about the same issue between fiber and aluminum. It's scary, but does ANYONE foiling in fresh water really disassemble their foil except for winter storage?
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boardsurfr



Joined: 23 Aug 2001
Posts: 1266

PostPosted: Wed Aug 28, 2019 12:52 pm    Post subject: Reply with quote

I've seen plenty of aluminum-carbon corrosion when using "hybrid" booms for a few years. The corrosion issue was definitely one of the things that pushed me to carbon booms.

Sounds like you are describing a personal experience. Some questions:
- Did you foil in salt water or fresh water?
- Did you rinse the foil after each session?
- Did you store the foil horizontally or vertically?
- How long did you leave the foil assembled?
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grantmac017



Joined: 04 Aug 2016
Posts: 946

PostPosted: Wed Aug 28, 2019 1:57 pm    Post subject: Reply with quote

Carbon to aluminum is FAR worse than simply stainless and aluminum. Especially inside the socket on slingshot stuff since the paint on the fuselage is scuffed each time it's inserted.

I sail in salt water and I coat the entire inside with Teflon pipe "dope". Lanolin or Tefgel are also good options. I flush with fresh water at least weekly when using it daily or before any time it'll sit for more than a week.

I'm very tempted to make a new fuselage without any aluminum.
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boardsurfr



Joined: 23 Aug 2001
Posts: 1266

PostPosted: Wed Aug 28, 2019 6:55 pm    Post subject: Reply with quote

grantmac017 wrote:
Carbon to aluminum is FAR worse than simply stainless and aluminum. Especially inside the socket on slingshot stuff since the paint on the fuselage is scuffed each time it's inserted.

The electrochemical potential between aluminum and carbon is larger than between aluminum and stainless steel, so that makes aluminum corrode faster. In addition, stainless steel quickly forms a thin protective barrier of oxidized metal that reduces flow of electrons and further corrosion; carbon does not. Between the front wing and the fuselage, there's usually a bit of room for movement, which means that any corrosion layers will be disturbed, which further increases corrosion.

A couple of things worth noting is that chloride in the water makes the corrosion a lot worse. Chloride prevents the formation of a stable oxide barrier on top of the aluminum, and can dissolve existing oxide layers. When storing a foil that is partially wet with sea water, things can get worse over time in a non-linear fashion: the chlorides can make the water more acidic as corrosion progresses, which in turn speeds up corrosion. Seems that's what the OP experienced.

So if your foiling in salt water, always rinse with fresh water after each session, and disassemble everything on a regular basis!
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ldhr



Joined: 10 Apr 2000
Posts: 121

PostPosted: Thu Aug 29, 2019 12:28 pm    Post subject: Reply with quote

isobars wrote:
I knew about the corrosion threat with all the bolts/screws, but hadn't thought about the same issue between fiber and aluminum. It's scary, but does ANYONE foiling in fresh water really disassemble their foil except for winter storage?


NO. Slingshot provides marine grease with their carbon foils.
No issues with any type of corrosion in fresh water.

Salt water is another issue. Hardware that is supposed to be stainless steel started corrosion after one session.
Replaced with better stainless steel for Ace hardware in Hood FRIver - no problems now.
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grantmac017



Joined: 04 Aug 2016
Posts: 946

PostPosted: Thu Aug 29, 2019 1:37 pm    Post subject: Reply with quote

I didn't get any grease from Slingshot. They also claimed to have titanium fasteners, I find that highly suspect except for the 10mm. The others are all garden variety SS.

Likewise their aluminum isn't a marine grade (just chinese equivalent 6062) and the anodizing is very low quality. The NP and SB aluminum is much better quality/finish and doesn't have these issues from what I've seen.

That said regular washing and disassembly does keep it going for a while but I'd still put the lifespan under salt water conditions of even the best maintained at 2-3 years.
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neilsather



Joined: 20 Jun 2002
Posts: 14

PostPosted: Fri Aug 30, 2019 12:32 am    Post subject: Reply with quote

The aluminum-carbon corrosion does happen in fresh water and quickly. If you are using your foil and not removing the fuselage from the wing in 3 weeks or less?? your wing may not be able to be removed without extreme measures. Titanium fixtures supposedly do not suffer from galvanic corrosion. A titanium fuselage with a kryptonite mast seems like the obvious cure.
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ericandholly



Joined: 20 Jun 1999
Posts: 292

PostPosted: Fri Aug 30, 2019 9:42 am    Post subject: Reply with quote

I have used the SS 633 setup for over a year--carbon to aluminum. I take the bolts out maybe every three months to switch a wing etc. I see zero evidence of any corrosion of any kind. I use grease on the bolts and foil in fresh water almost daily from April through October.

Not doubting anyone's understanding of chemistry; simply reporting my experience.

E
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boardsurfr



Joined: 23 Aug 2001
Posts: 1266

PostPosted: Sat Aug 31, 2019 12:35 pm    Post subject: Reply with quote

neilsather wrote:
... Titanium fixtures supposedly do not suffer from galvanic corrosion. A titanium fuselage with a kryptonite mast seems like the obvious cure.

Laughing What planet are you from again? Laughing



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