How Can I Tell Electrolysis From Galvanic Corrosion?

MontanaAardvark

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That might be confusing, so how can I tell if my boat's electrical system is involved in the mysterious holes I get in my '05 Starcraft 16 DLX - or if it's just saltwater in the wrong places?

This post is by way of follow up to my previous post about a hole that appeared in my transom over a period of a few months while the boat sat in the garage. The post was in early June in this forum.

I've been wracking my brain over this for 6 weeks, now. I have holes in a couple of areas and only those areas. I have a few holes on both the port and starboard sides of my transom. These are only in the outermost portions (about 1/4 of the width?) and are close to the waterline or online with the deck. There aren't holes in the middle of the transom. I have three or four holes on either side in the forward part of the boat - in front of the side console - but well above the waterline. Instead of being in line with the deck, they're in line with casting platform about a foot above the deck.

http://www.pbase.com/montana_aardvark/image/156579156 Shows holes in the starboard bow, about a foot in front of the side console.

In my mind, since the holes on the bow end aren't near any wiring, the electrical system shouldn't be involved. I can see the ones in the transom possibly being due to a wire getting crimped where it shouldn't be, or a wire that got disconnected or something; but not up on the bow, and especially not on the port bow, around 7 feet from the wiring in the console.

This past weekend, I sanded and prepped all the holes, and then covered/filled them with Marine-Tex (boaters' Bondo). Last weekend, I added a kill switch on the battery to completely disconnect it. The only time current will be flowing in the harness is when I'm on the water.

Aside from pulling the outboard, pulling the transom, and rebuilding it, I'd really like to know if I can fix this. One guy I spoke with just said "get a can of Bondo and chase down the holes as they appear. You'll get tired of it and throw it out before the hull comes apart". A crude approach but possibly right.

That PBase director contains pictures of the boat, the holes, and a comparison photo of the holes about 5 weeks apart. I swear they grew in that time.


Thanks,
Bob
 

jbcurt00

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Lets make this a little easier to see:
156579092_zps878f828d.jpg

156579156_zps1df7a309.jpg

156579153_zpsb9d7f9f9.jpg

156184101_zps69d7f5ed.jpg

156173559_zps7b503475.jpg



No idea, but if they got worse while under cover & IN the garage this winter, there is definitely something going on.

If there was saltwater wet wood against unpainted aluminum, then I guess it could have chewed on it all winter.............

Starcraft hulls are a limited lifetime warranty, remind me, did you contact an SC dealer? And what'd they say?

EDIT: Forum rejected my pix post too. So had to add them to my PB acct to get them posted
 
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MontanaAardvark

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Dec 12, 2011
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Lets make this a little easier to see:
156173559

156184101

156579092

156579153

156579156

156579349


No idea, but if they got worse while under cover & IN the garage this winter, there is definitely something going on.

If there was saltwater wet wood against unpainted aluminum, then I guess it could have chewed on it all winter.............

Starcraft hulls are a limited lifetime warranty, remind me, did you contact an SC dealer? And what'd they say?



I spoke with the local dealer, who told me the warranty was first owner only. Since I bought it used I'm outta luck.

The boat's an '05, I bought it 2 1/2 years ago.
 

Watermann

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I believe they told him tough luck.

I don't think your going to be able to stop the spread of the corrosion and the more salt water she takes on the worse the problem is going to get. Either way galvanic or electrolysis it's the death of the boat if not stopped.

I'm sorry to say the only way I know is to go after the biggest problem right now, the transom. I would pull the motor off and yank that salt soak chunk of lumber out. Then kill the corrosion and repair the damage on the inside. That would buy your boat many more years on the water. There really isn't any other way to stop it and putting patches on the outside never works for long, the material just gets eaten out again around the patch.

I know your wanting to avoid the repair but the tear down would only take less than a day. the clean up and rebuild would depend on how much work needs done inside.
 

Krichbourg

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Do you think you may have pressure treated wood in contact with the hull?
 

Scott Danforth

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galvanic corrosion is electrolysis. its dissimilar metals (aluminum and stainless, or aluminum, stainless and copper) in a conductive environment. Salt makes it a conductive environment.

and that is what you have going on. It is either pressure treated wood (treated with salts) or salt soaked wood in your transom. either way, the transom wood needs to come out to stop the corrosion.

dont waste time attempting to band-aid it with bondo and keep band-aiding it until there is nothing left of the hull. aluminum corrosion needs to be cut out. you cant get the surface clean enough.

good news is that the boat is aluminum. take it to your local aluminum fabrication guy, he can cut out the old, weld in the new, blend it, and you wouldnt know any different after paint (proper method of patch) or he can slap on a section of aluminum on the inside and seam it on the outside and you have a hole to fill and an obvious patch on the inside.

most aluminum hulls are 5250 aluminum so they are easy to form.
 

MontanaAardvark

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Scott - my deep fear is that I do all of that: rip out the transom wood, rebuild the stern and give up a few months' worth of fishing weekends, spend a few hundred or a thousand bucks, only to find pinholes starting to show up again, because it's all been caused by a wire creating a ground loop that I didn't find. If you don't fix the root cause, you haven't fixed the problem. I want to be as sure as I can be that the root cause is what I'm fixing.

As I understand it, there are two bits of conventional wisdom on wiring an aluminum boat: one says to completely isolate the hull and don't allow it to be at ground potential, while the other says it's really hard to isolate the hull in practice with a #4 wire going to that 300 pound engine on the back, sot it's really OK for the hull to be at the same potential as your negative battery terminal as long as the hull isn't used as ground. The difference between ground and grounding. Everything gets two wires: power and ground (same diameter, naturally) and you never do the old car guy trick of picking up ground from a wire to the hull.

When I got the boat, I went up under the side console and found that the PO would strip wires back about two inches, twist them into a wad and wrap the whole mess with tape (which was predictably a gummy, sticky mess). Most of them were a couple of feet longer than they needed to be. I spent a few weekends cutting off wires and replacing the splices with crimp terminals. This past weekend, I found an unterminated hot wire lying in the stinking bilge! (Along with a few other things I've never seen in the bilge in the last 2 1/2 years, including a Miller Lite beer can!). But I haven't traced every single circuit in the boat to make sure the PO didn't do something stupid. Well, something else stupid.

I got a motivational talk once where the manage told us that old cliche' "if you bite the head off a live frog every morning, nothing worse will happen to you all day". I always said, "but if you do, you went through biting the head off a live frog for nothing". To me, doing this job will be like biting the head off the frog. What if I do that I still don't stop the corrosion process? What if I do that work for nothing?


Bob
 

Watermann

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You can only do what you can do. I know we're all different. Personally I would enjoy spending the time and money to repair my boat rather than just drop 10 times the money on new although I could if I wanted to. While waiting for the glue and treatment of the transom wood to dry. I would tear out the entire wiring harness and be sure there was nothing unexpected when it went back in.

The thing is from what I've seen for the corrosion to take place there has to be water as a conductor for the electrolysis to take place. Your transom had a leak that I would bet saturated the plywood with saltwater causing what your dealing with.
 

GA_Boater

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Montana - I hope you can get this under control before it's too late. I think you have a plan for the wiring. I hope you also plan on replacing the wood. The pics look like the transom with the plywood showing. Usually I feel spar treated wood is perfectly OK. In your case I can't recommend anything but a protective application of epoxy and cloth for a more durable and near water tight wood seal. And lots of 3M 5200 on every penetration of the hull and wood.
A note on the wiring. Like you said about not using the hull as a return, you don't want current flowing thru the hull to turn on a light bulb, make sound from a radio or allow any electrical device to work. Dedicated ground and power busses are the only way. An metal hulled boat is naturally at battery ground or negative potential because the battery negative is connected to the motor and the ground path is completed through the clamp/swivel to the hull. What I'm trying to say in too many words is a complete rewire is an excellent idea. I know the live wire in the bilge didn't matters at all.
 
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Scott Danforth

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the "live" wire you found was not helping matters.

however since you have to patch the hull, I would probably install a new wiring harness like GA mentioned. I would make the harness while the boat is being repaired.
 

MontanaAardvark

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Thanks. I have suspicions about the wiring harness, but I'm pretty sure my problem is not due to the wiring. I have a couple of holes that are along the port bow, probably 7 feet from the console. There's no reason for current to be circulating that far forward. The only wiring up there is to the bow lights and I never go out at night, so there's never any current flowing up there.

I guess the answer is to replace the transom with new plywood or MDF or something; probably two 3/4 pieces laminated. And then covered in fiberglass? Because, if not, what's the difference between that wood and what's in there now? (Assuming water still gets back there somehow).

Has anyone used structural foam, like the airplane builders use? At least that won't rot.


Bob
 

jbcurt00

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I guess the answer is to replace the transom with new plywood or MDF or something; probably two 3/4 pieces laminated. And then covered in fiberglass? Because, if not, what's the difference between that wood and what's in there now? (Assuming water still gets back there somehow). Has anyone used structural foam, like the airplane builders use? At least that won't rot.
Bob
Use MDO not MDF

The plywood transom you have now is probably not sealed at all. So if it gets wet, anywhere near a saltwater environment, it could trap saltwater between the wood & aluminum because it's soaked into the wood.

A sealed plywood transom won't hold water like unsealed will, so there's less opportunity for water (esp saltwater) to be sitting between the plywood & aluminum skin.

You can use poly resin & fiberglass if you wish. Most use epoxy alone or 'just' spar varnish. Both have benefits and using either is better then nothing..............
 

Watermann

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The whole goal is to repair the skin so as no water will be able to make it's way in between the wood and skin ever again. I've burned through a construction tube and a half of 5200 and 2/3 rds of a tube of 4200 on my Chief. Every hole has to be sealed up to keep water out of the transom area and the whole boat for that matter.
 

Bwana Don

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Chase your wires down. You should ground back to the battery and not to the boat anywhere. I agree with the mob, transom needs to be pulled out.
 
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