Electrolysis BAH!

[Maynard Rupp]

We have discussed this topic to death in past threads, but mine is a bit different. I had a problem 2 years ago that I thought was cured by adding a galvanic isolater. We were eating anodes so badly that we had to change tham every 3 months. Since I did that install we can go a full year before changing the anodes. I hauled the boat last week for bottom paint and hull polishing. It has been in the water in Miami for 2 years. The bottom paint is Petit Trinidad Pro and that held up very well. 2 years ago I also bottom painted the struts, rudders, and gratings that go over the thru-hull inlets. I did not prime them.

So much for the history. When we hauled I noticed a copper type rough layer on the hulls paint and around many of the brass parts including struts etc. The paint that I applied to the brass parts was completly gone with no evidence that I ever painted the stuff. A yard worker said that I have a wire missing or broken on the grounding system. Well, I checked that with an ohm meter because of this problem 2 tears ago. I removed every wire, cleaned the ends, even though they looked like new, replaced them and sprayed all connections with Bo-Shield T-9. All of my copper strips are like new and sprayed also. I just ran around with my meter and find what seems to be a perfectly connected ground system. This time I applied 2 coats of an Interlux barrier primer that the yard guy recommended before painting the brass stuff. I tried not painting that stuff 3 years ago when we still used VC-17. That was when I first noticed that copper plating. I thought that bottom painting the brass parts would help. I was sure that we had the problem solved when the Galvanic Isolater stopped the anode loss. I should mention that this is the third haulout in the 5 years that we have had the boat in salt water and we have had this hull plating every time.

 

[REBrueckner]

I assume your zincs are ok and the issue now is that the paint is gone. What do instructions call for on the Trinidad....If the zincs were "normal" I'd not worry...Is your isolator monitored....if not it's a good idea to test it as diodes can burn out....

If you use your boat a lot more or less in a given period that will affect paint performance. I found when I cruised six months continuously the paint ended up disappearing from props and shafts but they stayed pretty clean because of use...so I stopped having them "specially treated" with the expensive multiple coat crapola...others have found it very useful.

I always used to paint underwater bronze parts directly with copper based antifouling paint....before my Hatt....sometimes it stayed on, especially once the paint got built up and thick, sometimes the parts were pretty clean of paint. Analogous to the hub of a prop where paint tends to hang on versus the tips where water abrasion wears off most of the paint.

There is little galvanic action between copper and bronze (they are very close on the galvanic potential scale) but generally speaking the adhesion of copper based paints doesn't seem so great on either bronze nor stainless shafts....

 

[fissioneng]

When we hauled I noticed a copper type rough layer on the hulls paint and around many of the brass parts including struts etc. The paint that I applied to the brass parts was completly gone with no evidence that I ever painted the stuff. (

It sounds to me like your paint is just really worn out and built up assuming it is a hard paint. Some of the copper has stayed stuck together, but all the other components have washed away.

With all you have done with the isolator and bonding system, I don't think this has anything to do with electrolysis with your zinc consumption that low.

Maybe time to change to an ablative paint?

 

[67hat34c]

What did the through hulls look like, were they copper color also?

 

[Pascal]

i thought you were not supposed to paint the bronze parts like struts, rudders, shafts, thru hulls (they're not brass afaik) since the metal in the paint will react witht he metal on the hull. unless you use paint specifically formulated for metal, but it my experience it's just not worth it.

if you're gettign a year out of the zincs, it's pretty good. sounds like a case of if it aint broken dont fix it.

 

[Craig]

i thought you were not supposed to paint the bronze parts like struts, rudders, shafts, thru hulls (they're not brass afaik) since the metal in the paint will react witht he metal on the hull. unless you use paint specifically formulated for metal, but it my experience it's just not worth it.

if you're gettign a year out of the zincs, it's pretty good. sounds like a case of if it aint broken dont fix it.

Based on the nobility chart, the above statement is pretty much totally untrue. Brass, stainless, copper, and bronze are in the more noble class, that's why we use zinc, in the least noble class. I consider myself an amatuer boater compared to a lot of people, but in 50 years of boating I have never heard of bottom paint causing corrosion, or electrolysis problems. Now cheap bottom paint? well who knows?

 

[Pascal]

LOL you're right... big brain fart!

 

[Maynard Rupp]

What did the through hulls look like, were they copper color also?

Yes, and the baskets that go over them were painted both inside and out. When we hauled there was no bottom paint anywhere on those brass baskets. This rough surface plating is around most through hulls, where the struts and rudders meet the hull. We vhad bthis with the VC-17 and again with the Petit Trinidad Pro. We completly removed the VC-17 and left only the 7 coats of barrier coat. Then we applied the Petit paint. That was 2 years ago and I see the same thing now.

 

[Craig]

Yes, and the baskets that go over them were painted both inside and out. When we hauled there was no bottom paint anywhere on those brass baskets. This rough surface plating is around most through hulls, where the struts and rudders meet the hull. We vhad bthis with the VC-17 and again with the Petit Trinidad Pro. We completly removed the VC-17 and left only the 7 coats of barrier coat. Then we applied the Petit paint. That was 2 years ago and I see the same thing now.

Try this site it may help. One of the better explainations I have seen.

marinesurvey.com/yacht/

 

[fissioneng]

Yes, and the baskets that go over them were painted both inside and out. When we hauled there was no bottom paint anywhere on those brass baskets. This rough surface plating is around most through hulls, where the struts and rudders meet the hull. We vhad bthis with the VC-17 and again with the Petit Trinidad Pro. We completly removed the VC-17 and left only the 7 coats of barrier coat. Then we applied the Petit paint. That was 2 years ago and I see the same thing now.

I'm a little confused. If your underwater metal IS bright copper colored, I believe you have dezincification going on and a stray current corrosion problem despite all your efforts.

The way I read this, your paint on the bottom is showing copper, not the underwater metal. Please clarify.

 

[captddis]

Need pictures! If you did not sandblast your hardware then go through the 5 step process, the paint will not stick. Not sure what plating you are talking about, however there is an orange/pinkish color marine growth that looks like electrolysis but is in fact just growth. It scrapes off. If your metals are a nice bronze color and not pink, you do not have a problem. I have a feeling you are chasing a problem that is not there.

 

[Maynard Rupp]

I'm a little confused. If your underwater metal IS bright copper colored, I believe you have dezincification going on and a stray current corrosion problem despite all your efforts.

The way I read this, your paint on the bottom is showing copper, not the underwater metal. Please clarify.

I guess I said copper, but I sure did not submit that stuff that I scraped off to a metalurgist. Under water metal is bright except for the barnacles, but I see no metal loss. I wish I had taken pictures. The plating is black and rough. You can scrape some of it off and then you see something copper color. The rest I ground off to the bottom paint and barrier coat. The stuff is very hard and on top of the existing bottom paint. Your explanation sounds like the answer, but I am scratching my head to try and figure out why!

 

[Maynard Rupp]

Need pictures! If you did not sandblast your hardware then go through the 5 step process, the paint will not stick. Not sure what plating you are talking about, however there is an orange/pinkish color marine growth that looks like electrolysis but is in fact just growth. It scrapes off. If your metals are a nice bronze color and not pink, you do not have a problem. I have a feeling you are chasing a problem that is not there.

I don't have pictures, but it would be hard to see anyway. I ground all the metal with 60 grit, wiped with MEK, and this time, I primed with a recommended Interlux barrier/primer, (2 coats). I then painted. Last time, I ground and bottom painted. I was unable to find a single scrap of that paint that I applied, even up in the bedding pocket area by the hull. Gee, I guess it could be marine growth, but why just around the brass parts and through hulls.

In my search with my ohmmeter, I found perfect and clean, (no green), bonding, but, I have 4 through hull fittings for speed and depth. The speedo ones are plastic, but the depth pickups are brass. There is no provision on any of these for a ground wire, and they don't have any. I have never seen any depth transducers that are bonded either. Mine are both high dollar Airmar units.

 

[REBrueckner]

well I no longer understand the description,
Is your issue captured in any of the photos from Pasco....

marinesurvey.com/yacht/


references above to BRASS are almost certaintly incorrect....hull fittings are bronze....and if bronze fittings get that pink tinge, then there is some corrosion present....but if zincs are in place this is rather unusual....

 

[SKYCHENEY]

Maynard,
My transducers have a bonding wire that is held to the side of them with a hose clamp.

 

[spcoolin]

I too am at a loss about the copper or brass color reference...Bronze has it's own color...If it gets colored like copper then you have a problem.

One thing I didn't see mentioned...You could be over zinc-ed, meaning over protected, and that will cause the paint to do as you describe around underwater metal...

Has anyone checked your potential with a corrosion meter & a silver:silver chloride probe while in the water ?

You should not show more than say 700-800 millivolts...Over that and you will need to remove some zinc.

Steve~

 

[REBrueckner]

Post 16 about over zincing makes a good point....a simple way to test is to remove a bonding wire from a thru hull for a season and see if that stops the effect you are experiencing...thru hulls don't need bonding anyway so there is no "risk".....

your bonding wire system might also be picking up stray leakage currents from the water...so check nearby boats to see if they have the same problem...if not, it's not likely that is an issue.

 

[Maynard Rupp]

Thanks Bob and everybody. I am afraid I used the term brass and bronze and maybe even copper as synonyms. I realise that they are different. Whatever Hatteras used is what I have. The zincs on this boat are the same as the original group from the factory except on the trim tabs. We originally had one pancake zinc on the inside of the tab with a bolt. It is easier to install them the way they come, so we now have one on the inside and one on the outside. Something else that I forgot to mention is that the stainless trim tabs have that rough black plating both inside and out. The anodes on the tabs also last a full year. Sky, I will buy some green wire, hose clamps, and ground both of my depth transducers, Thanks.

 

[jim rosenthal]

Maynard, I would do a couple of things here: first, read Nigel Warren's "Metal Corrosion in Boats", I think it's called; excellent and very readable book on all this. Second, find a corrosion consultant and get them to do an in-water survey on Unity, which is done exactly as noted above, with a reference electrode in the water around the boat, and read your boat's bonding system. Third, find out from your dock neighbors if they have the same problem.

If you galvanic isolators are working as they ought to, you probably don't have a DC problem in the bonding system, but I'd be concerned, too, and I'd want to know. Without photos, as they say, it's hard to know what you're describing.

My metal boat years ago (a Striker) was fitted with a Capac meter, so the boat had it's own reference electrode and you just took readings every now and again. Capac is still in business, but the meters are digital and much improved. There isn't any reason you couldn't put a Capac meter on any other boat, and for someone in a tropical environment and a busy marina with possibly a lot of stray current around, it might make sense.