Electrolysis of the bottompaint ?

[dc380]

Anyone know what's going on here? The bottompaint is gone, on the trim tab and transom. The Zinc is still brand new. You can still read the manufactor name on the zinc.

Both tabs look like this, same with all the underwater metals. An area around all the metals, the paint or copper is gone.

The Hull zinc is 10% gone. None of the metals are damaged or pitted. Just the copper paint is done.

I tested all the underwater metals and they are bonded to the hull zinc. :huh:

 

[dc380]

Would anyone know where I can find the Galvanic Isolator on a 380DA? :smt100


802074 GALVANIC ISOLATOR, ZINC SAVER II 30AMP

 

[bahamabreisus]

i would be more concerned about how your running looks.

 

[Tabman]

DC380,

Two quick questions; is there good electrical contact between the zinc anode and the Trim Tabs (i.e. no paint under the zinc and a good clean surface)? And, is the situation the same on both Trim Tabs or confined the the starboard side shown in the picture?

Happy Thanksgiving,

Tom McGow
Bennett Marine

 

[dc380]

The props and shafts were fine, they were relatively barnacle free. No pitting, and the paint on the shafts is still there. Both zincs were still there, although they were mostly gone. The rudders were clean, except where they connect to the hull. Where they connected was covered with barnacles, and the paint was gone.
Same with the underwater exhaust, the base was covered with banacles.

The zincs seem to be doing their job protecting the underwater metals. It's the bottom paint close to the metal that's being affected.

 

[dc380]

DC380,

Two quick questions; is there good electrical contact between the zinc anode and the Trim Tabs (i.e. no paint under the zinc and a good clean surface)? And, is the situation the same on both Trim Tabs or confined the the starboard side shown in the picture?

Happy Thanksgiving,

Tom McGow
Bennett Marine

Hi Tom

I wire brush the area under the zincs down to bare metal, before attaching the zincs. I also use a templete cover which adheres to the tab so that area stays paint free, while I paint.

Yes, but trim tabs look the same.
I have more pictures I can post, that would help?

Dave

 

[Tabman]

Hi Tom

I wire brush the area under the zincs down to bare metal, before attaching the zincs. I also use a templete cover which adheres to the tab so that area stays paint free, while I paint.

Yes, but trim tabs look the same.
I have more pictures I can post, that would help?

Dave

If the other side looks the same, I don't think there is a need for more photos. Sounds like you are doing everything correctly with the Trim Tab zincs.

One thought is that perhaps the original bottom paint was not applied over the paint manufacturer's priming system, or the priming may have been compromised by sanding for subsequent applications of bottom paint.

Usually priming is accomplished using a two part system and side effect is that it "isolates" the metal content in the bottom paint from the Trim Tab.

You may want to consider stripping the Trim Tabs down to bare metal and reapply the priming system (following the masking you do for the zincs). And then reapply the antifouling paint.

Tom McGow
Bennett Marine

 

[dc380]

Thanks Tom

I did not re-prime last year.

I will strip it this spring and re-prime starting from bare metal.

Happy Thanksgiving

thanks
Dave

 

[Redhook98]

It looks like you may be OVER-protected. The first sign of being overly-protected is paint blistering and removal. Looks like a classic case from what I have seen.

 

[dc380]

Redhook

It's interesting you mention that, because a 380DA not far from my boat had no barnacles or paint failure. He had no shaft zincs, a 3" zinc on each tab, and hull zinc.

I had 2 shaft zincs, a 6" zinc on each tab, and Hull zinc.

Maybe I should be asking what other 380 folks use for zincs?

Dave

 

[Redhook98]

Usually if it is blistering paint, etc, then it is more then just an extra zinc. You should use a silver-silver-chloride probe and test what your protective cathodic reading is. You should be around -0.9 to -1.1 volts.

 

[dc380]

I purchased a tester from Boatzincs last season.

I tested at the begining and end of the season. At the begining I show .880 and at the end .870 I think that's close to being good?

There is likely more then 1 thing going on here. Just don't know what to check next.

 

[Redhook98]

Yeah, those readings are close enough where this should not be happening. I agree. It sounds like you have multiple things going on. Did you check it with your shore cables attached, and unattached? I have gone so far as to test the boats in my proximity before. It just seems to localized to the classic "over-protected areas" to be a simple improper paint job. I have done real shoddy paint work before and never had it come off like this......

 

[dc380]

Yes, I plugged and unplugged the shore power, and I turned on and off all AC and DC switches, including the Radar, bilge pumps, ran the engines Nothing made the multimeter move.

One suggestion I got was to check the altenator. I did but only at idle. I need to check it again in the spring under load.

I tested the props and shafts and they are connected to the bonding system. There was continuity between the hull Zinc and the prop and shaft. So I may not but zincs on the shafts next season.