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Old 07-06-2018, 06:30   #1
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Galvanic corrosion around boom bail

I was re-seating hardware on the mast and boom the other day, as I've noticed galvanic corrosion around a number of fittings, when I discovered that the corrosion around the boom bail was particularly worrisome.

Let's say the boom and bail fitting aren't compromised, how should I address this? Drill out the old rivets, clean the area thoroughly, install new (Monel? Stainless Steel?) rivets with Tef-Gel?
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Old 08-06-2018, 12:58   #2
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Re: Galvanic corrosion around boom bail

Well, I drilled out the rivets today, and the corrosion looks pretty bad. Spar replacement isn't an option right now, but what steps can I take to make sure the strength of boom isn't seriously compromised, and when I re-install the boom bail, should I move it to a new location either slight forward or slight aft of its old location?
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Old 08-06-2018, 13:07   #3
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Re: Galvanic corrosion around boom bail

Drill the hole bigger and get long bushings. Insert the thru bolt into the bushing and tighten up. Don't move the hole.
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Old 08-06-2018, 13:12   #4
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Re: Galvanic corrosion around boom bail

I'd use a grinder or wire wheel. Clean off the corrosion, fit a small (2 or 3") plate over each side, redrill the same hole in the same place and just use tefgel or other protection on it from time to time. Booms are usually aluminum, bails are usually steel, maybe you can get an aluminum bail. Or just keep the new plates well protected.
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Old 08-06-2018, 13:43   #5
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Re: Galvanic corrosion around boom bail

Use an SS wire wheel or better a scotchbrite wheel.
Regular steel wheel will embed steel particles in the aluminum which of course will quickly rust.
You want to treat the bare aluminum somehow, maybe just alodine it, but don’t leave it bare.
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Old 08-06-2018, 13:51   #6
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Re: Galvanic corrosion around boom bail

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Originally Posted by hellosailor View Post
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>
Booms are usually aluminum, bails are usually steel, maybe you can get an aluminum bail. Or just keep the new plates well protected.

It' a classic dilemma in the true sense of the word.


The bolts are steel. The boom is aluminum. Somethin's gotta give.
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Old 08-06-2018, 15:22   #7
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Re: Galvanic corrosion around boom bail

Ryban,

The reason for re-using the holes is that you don't want to add more, for a "tear along the dotted line" effect.

Yes, to cleaning off all the corrosion products. Then, use an aluminum primer, prime it, then paint it, to keep out the salt water. When you reinstall the bale, use something for a physical barrier*, and use antiseize if you re-rivet it. I would seriously consider using a bolt and double nutting it on the other side. You can wrap the bolt with electric tape on it's shaft, and paint the flat of it with liquid 'lectric tape. Do the best you can to insulate the s/s from the aluminum. Keep an eye on it, and see how you go.

* there are nylon washers; you can use a bit of tire inner tube, pvc tape, lots of things one might use.

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Old 08-06-2018, 18:21   #8
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Re: Galvanic corrosion around boom bail

The local chandlery had some 1/4" Monel rivets, but no 1/4" bolts long enough to make it through the boom and out the other side. They had 5/16" ones though that would do the job, but I don't have a lot of space on the boom bail to safely widen the hole.

What is meant by 2-3" plates? Are we talking about thin aluminum sheeting glued in place to act as a spacer and sacrifice itself in the event that there is further corrosion, or am I misunderstanding? My main concern with doing something like that is that if there were any further corrosion, it would be hidden behind the aluminum plates.

I think cleaning the oxidation off, priming, and painting is a good idea. As I understand it though, once aluminum is exposed and oxidized, further (non-galvanic) corrosion is inhibited, correct?
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Old 10-06-2018, 02:54   #9
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Re: Galvanic corrosion around boom bail

Inhibited is the right word. It is that with dissimilar metals, you try to put coatings between them. Duralac is popular in Oz. We used to use silver antiseize, but more anhydrous lanolin now, but, for your application there, with the rivet, boom and bale, something like Duralac would be good. The more closely the dissimilar metals are in contact, the greater the problem. Liquid Lectric Tape also could work. Duralac is made for the purpose, though.

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Old 10-06-2018, 03:56   #10
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Re: Galvanic corrosion around boom bail

Another great product is Tefgel.
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Old 10-06-2018, 06:55   #11
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Re: Galvanic corrosion around boom bail

I’d do either tefgel or lanocoat also use nylon washers between the bail and the boom.
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Old 10-06-2018, 07:13   #12
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Re: Galvanic corrosion around boom bail

What Stu said is what they do on masts. It distributes the bearing area better also. Use a piece of aluminum tubing.
Of course you could have pads welded to the boom, or riveted. Or you can use a strop on the boom instead of a bail and get rid of the corrosion problem.
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Old 12-06-2018, 12:05   #13
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Re: Galvanic corrosion around boom bail

I managed to find 1/4" Monel rivets here, but I also found a 1/4" stainless steel bolt that is long enough to do the job, and I think I prefer this option for easier disassembly.

What is the advantage of using an aluminum bushing in addition to a through-bolt? Is it just that the bushing will corrode instead of the boom, or is there also a mechanical advantage that I am missing?
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Old 12-06-2018, 12:28   #14
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Re: Galvanic corrosion around boom bail

A bushing is sacrificial and easily replaced if it wears or corrodes, rather than repairing a larger hole in the boom. "Plates" referred to yes, sticking patches on the boom, to locally make it thicker and more resistant to corrosion. You'd need to properly bed them and adhere them, and in doing so there would be no question of corrosion under them.
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Old 12-06-2018, 17:37   #15
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Re: Galvanic corrosion around boom bail

Quote:
Originally Posted by Ryban View Post
I managed to find 1/4" Monel rivets here, but I also found a 1/4" stainless steel bolt that is long enough to do the job, and I think I prefer this option for easier disassembly.

What is the advantage of using an aluminum bushing in addition to a through-bolt? Is it just that the bushing will corrode instead of the boom, or is there also a mechanical advantage that I am missing?
Bushing:
-You cut out the nasty corroded hole to clean metal with the larger hole for the bushing.
-The bushing outside diameter distributes load over a larger area than the original design.
-The bushing eliminates compressing the boom when you tighten the bolt.
-If you ever want to get the bushing out you better coat it with lanolin or tef gel.
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