Paint flaking off Rudder

[ScottA]

Hi all,

Had the boat hauled out and made the following discoveries, flaking antifoul off metal parts; Rudder and shaft bracket covered in small bubbles, looking like the remainder paint is about to lift.
Antifoul flaking around the two brass intakes
The transom anode is bright where it is consuming, there is an anode on the shaft that appears to be normal.
The marine electrician suspects stray current from an outside source - Shore power earth wire and has suggested the fitting of a galvanic isolator?
I have read a bit about it and it seems the anodes should be very consumed before an attack on the other harder metals?
Would appreciate your opinions
Thanks Scott

 

[sunchaser]

Something to consider, build issue from Beneteau. Bonding and electrical system design and integrity should not be overlooked. Is anyone else near you in the marina suffering similar problems? Shore side determination of stray current can be tested to assess whether boat or environment is the problem.

Has any electrical work been done on boat recently? A dock mate in my marina sent his KK42 to the bottom two weeks after he was working on ground and bonding systems as brass through hulls got eaten up.

 

[Larry M]

Was the metal parts cleaned or primed prior to the last anti foul application? The rudder looks like the paint is coming off in sheets.
Maybe an adhesion issue?

Once you renew everything and are back in the water, have a corrosion analysis done by someone that knows how to use a silver/silver-chloride electrode.

 

[C lectric]

I was going to leave this entirely alone but will make a few comments.
First be sure that the failing paint isn't due to lousy prep work. If the primer wasn't put over absolutely clean metal or fiberglass it can fail.
If the weather was too cold paint can fail.

Too much zinc or overzincing can cause paint failures although there would have to be a lot too much.

Yes, a AC ground wire galvanic isolator is a good idea but they are not foolproof. Read about them. Get one.



If you do not have a good Digital Clamp on Ammeter, a silver/silver chloride cell, a good Voltmeter/DMM and understand how to use them with some knowledge of what you are doing then get a good MARINE ELECTRICIAN down there.

Real AC leakage can be deadly and any leakage, AC or DC, can sink boats. Even if not sunk a lot of damage can be done if let go for even a short period. Do not fool about.

The problem could be aboard your own boat, the marina wiring or a neighbours boat, either next door or a few boats away.

If your boat appears to check clean then get the marina involved particularily to make them aware and also if other boats or their own system have to be tested.

 

[boatpoker]

What the anodes look like tells you almost nothing. You must test for continuity between the anode and the metal to which it is attached. You should see much less than 1ohm.

A few years ago I tested about 40 boats in a yard and found two with continuity. The photo below shows Open Line or no continuity.

 

[fstbttms]

Looks like improperly primed metal to me.

 

[Aquabelle]

I too think it a paint failure. But get Craig from Fleetmarine at Bobbin Head to meter your bonding system, just in case. Not too much wrong with the Bobbin Hd marina's electrical system that would cause this. You should get a galvanic isolator anyway

 

[ScottA]

Thank you all for your responses, it gives a better insight to the problem.
I now have a galvanic isolator fitted to the boat, when tested the marine elec said that it had dropped 10 milliamps, so the current is now a little below average instead of a bit above, the rudder has been repainted so will be eager to see what has happened when it comes out in Sept for antifoul.
Does anybody have any idea why the antifoul is flacking on the hull around the brass through hulls?
Thanks Scott

 

[boatpoker]

Thank you all for your responses, it gives a better insight to the problem.
I now have a galvanic isolator fitted to the boat, when tested the marine elec said that it had dropped 10 milliamps, so the current is now a little below average instead of a bit above, the rudder has been repainted so will be eager to see what has happened when it comes out in Sept for antifoul.
Does anybody have any idea why the antifoul is flacking on the hull around the brass through hulls?
Thanks Scott

That sounds like a galvanic reaction between a high capacitance anti-fouling paint and the brass. Brass is a very poor choice for throughull fittings.

Many anti-fouling paints have metals in them. If the metal is further up the galvanic scale than brass .... the brass looses.

Read Yachting Monthly on brass throughulls.

 

[fstbttms]

Does anybody have any idea why the antifoul is flacking on the hull around the brass through hulls?

That sounds like a galvanic reaction between a high capacitance anti-fouling paint and the brass.

That is exactly what is going on and again, the result of improperly primed metal.

 

[ScottA]

Thanks for your further help,
I have just generalised calling the underwater fittings brass, they well could be bronze or Nicad?
I have noticed the zinc bonded transom anode is now not as bright in the consumed area after the fitment of the galvanic isolator abt ten days ago, so this may have improved the situation. Time will tell
Regards Scott

 

[Aquabelle]

Scott: on your boat, I would be very confident that the thru'hulls are bronze, not brass. Also, next time you are due to replace your transom anode, you might consider using the newer aluminium ones instead. They work really well in the Hawkesbury/Cowan/Pittwater waters and in my own case (vessel normally at Bobbin Head...will be back from Qld in a couple of weeks weather permitting) changing to the aluminium anodes has added a good 6-8 months of life over zinc. Craig at FleetMarine there at the marina suggested it and he metered my boat before and after & they are working perfectly. Also, do you have shaft anodes on your running gear? You can get a better result with spring-loaded shaft brushes INSIDE the boat. Happy to show you mine if interested when I get back; again you could ask Craig about these. They are essentially maintenance free and don't wear out vs shaft anodes which need annual replacing and can fall off earlier, as happened one year to mine after just a few months. Unless you dive your boat regularly, you are not likely to discover the shaft anodes have disappeared until she's hauled...by which time, some damage will likely have already been done.

 

[ScottA]

Thanks Aquabelle,

Would like to meet you and view the shaft brushes, let me know when you return

Regards Scott