tiny bumps on lead keel

[PeterWright]

So for the first time ever in 13 years, this Fall I have these little bumps on my keel only, none on the hull. Never had a single one, now I have hundreds. I suspect it's electrical related. I noticed that the anode on my prop shaft just spins, perhaps the culprit.

There were no known changes to the electrical setup of the boat in the past 3 years.

First, is this an electrical issue like I suspect?
Would the loose prop anode explain this away?
Could a neighbors boat have had any effect?
What other damage might have been done that I don't know about / can't see?

[psk125]

Is it a cast iron keel? I have seen "bubbles" of iron oxide (bigger than your photo shows) form in the antifouling paint on a cast iron keel that had issues with electrical fields near their slip not being properly grounded. The keel I saw only had the problem on one side, because that was the side with the electrical issue.

[MicHughV]

I've never known a lead keel to grow bumps, so I suspect it is a metal keel. I see, what looks, like rust on the trailing edge ??

On a rare occasion, I have seen a lead keel, that had some iron objects cast into the lead, but never seen those spots before.

[Jim Cate]

I've never known a lead keel to grow bumps, so I suspect it is a metal keel.

Umm... ain't lead a metal?

For the OP: what sort of vessel is she? And what do you find if you scrape the blisters a bit?

Jim

[MicHughV]

no, lead is a vegetable, it doesn't grow spots. Steel, on the other hand, is a fruit, and on occasion suffers some or other "blight"....didn't ya know...

[PeterWright]

The keel is lead.

Any helpful suggestions?

[PeterWright]

If I scrape them, they will come off, but leave a pit in the epoxy.

[Fishspearit]

Lead is very noble, so I don't think it's because of your inactive zinc. If you're zinc was not working the other metals like bronze and stainless would be anodic to the lead keel and they could suffer galvanic corrosion but not the lead.

Absent some other problem such as stray current, I would first suspect the antifouling coating. Did you change types? Was it a copper based anti-fouling in which the copper would be anodic to the nearby lead keel?

[Lee Jerry]

When was the hull last painted? Is it contamination splattered on the keel prior to painting? Could both affect adhesion and also a reaction under the paint (similar to but not osmotic blistering).

[Bill O]

Originally Posted by PeterWright

The keel is lead.

Any helpful suggestions?

Double check with a magnet to make certain it is lead. What boat is this keel on?


When the boat was being prepped for the epoxy, did anyone do any steel grinding under your boat?

[s/v Jedi]

I have steel contamination in my lead keel but that doesn’t look anything like that.

I bet you have electrical wiring connected to underwater metals?

I have seen a stainless steel anchor chain being eaten away and it showed the same shape damage.

Is the shaft zinc the wrong diameter? If it was eaten away on the inside then that’s something I never saw, but at this point all evidence shows an electrical problem that can only happen if your underwater metals are connected to wiring.

[Fishspearit]

Originally Posted by s/v Jedi

I have steel contamination in my lead keel but that doesn’t look anything like that.

I bet you have electrical wiring connected to underwater metals?

I have seen a stainless steel anchor chain being eaten away and it showed the same shape damage.

Is the shaft zinc the wrong diameter? If it was eaten away on the inside then that’s something I never saw, but at this point all evidence shows an electrical problem that can only happen if your underwater metals are connected to wiring.

That is entirely incorrect. You're describing stray current corrosion, and your unorthodox electrical views are MORE likely to result in stray current corrosion while a properly wired and bonded boat to ABYC standards is LESS likely to suffer stray current corrosion.

Lets look at the classic stray current corrosion example. A wire comes loose from a splice or crimp (yea, yea, it will never happen to YOUR wiring) and the wire falls down and the exposed end lays against one of your sea cocks. Lets assume they are bronze for this example. With your unorthodox wiring system that sea cock is at +12 or +24 volts. It becomes the cathode and the nearby sea cocks begin shedding ions (bits of metal from your sea cock) and within a day or so that sea cock will be completely dissolved and you'll have a hole in your boat.

Now lets look at a boat wired to ABYC standards. +12V wire drops onto a bonded sea cock, completes the circuit back to the battery, fuse or breaker open the circuit and there is no stray current corrosion.

So to reiterate: SV Jedi unorthodox wiring=more likely to suffer stray current corrosion
ABYC standards=designed to reduce the risk of stray current corrosion.

[s/v Jedi]

Originally Posted by Fishspearit

That is entirely incorrect. You're describing stray current corrosion, and your unorthodox electrical views are MORE likely to result in stray current corrosion while a properly wired and bonded boat to ABYC standards is LESS likely to suffer stray current corrosion.

Lets look at the classic stray current corrosion example. A wire comes loose from a splice or crimp (yea, yea, it will never happen to YOUR wiring) and the wire falls down and the exposed end lays against one of your sea cocks. Lets assume they are bronze for this example. With your unorthodox wiring system that sea cock is at +12 or +24 volts. It becomes the cathode and the nearby sea cocks begin shedding ions (bits of metal from your sea cock) and within a day or so that sea cock will be completely dissolved and you'll have a hole in your boat.

Now lets look at a boat wired to ABYC standards. +12V wire drops onto a bonded sea cock, completes the circuit back to the battery, fuse or breaker open the circuit and there is no stray current corrosion.

So to reiterate: SV Jedi unorthodox wiring=more likely to suffer stray current corrosion
ABYC standards=designed to reduce the risk of stray current corrosion.

You are 100% wrong. The OP has no broken wires that fell on bronze seacocks, causing his lead keel to be eaten away. This is pure fantasy.

Also, even when a +24V wire would connect with underwater metal, there will only be a current when a circuit has been completed.

It is unbelievable how people think current will flow when there is no completed circuit. Even just simple logic will tell anyone that when you only connect the dc positive to something that it doesn’t work because you also need dc negative. I believe this is caused by not just ignorance but also because people get confused with shore power systems using grounded neutrals and now they think their dc negative is somehow also automatically connected to ground. The pointing to ABYC without any correct explanation shows that there is no engineering background.

Also, ignoring the fact that what I write is how most of the world does things is another sign. It’s not possible to cope with that thought.

[Fishspearit]

Originally Posted by s/v Jedi

You are 100% wrong. The OP has no broken wires that fell on bronze seacocks, causing his lead keel to be eaten away. This is pure fantasy.

I was giving an example, obviously, not describing the OP's situation.

Originally Posted by s/v Jedi

Also, even when a +24V wire would connect with underwater metal, there will only be a current when a circuit has been completed.

I agree

Originally Posted by s/v Jedi

It is unbelievable how people think current will flow when there is no completed circuit. Even just simple logic will tell anyone that when you only connect the dc positive to something that it doesn’t work because you also need dc negative. I believe this is caused by not just ignorance but also because people get confused with shore power systems using grounded neutrals and now they think their dc negative is somehow also automatically connected to ground. The pointing to ABYC without any correct explanation shows that there is no engineering background.

Your engine is grounded, right? The battery negative is there for your starter to work. You have an electrolytic path through the sea water (through your sea strainer). Ions flow through the water to complete the circuit, that's how stray current corrosion works. Especially in slow moving water. The completed circuit is there.

Originally Posted by s/v Jedi

Also, ignoring the fact that what I write is how most of the world does things is another sign. It’s not possible to cope with that thought.

No, your floating DC ground and no AC to DC grounding connection is not the marine industry standard. I gave a perfect example of how your setup needs only a single fault to have stray current corrosion while the industry standard design usually needs 2 or more faults. You just don't want to admit it.

[s/v Jedi]

Originally Posted by Fishspearit

I was giving an example, obviously, not describing the OP's situation.


I agree



Your engine is grounded, right? The battery negative is there for your starter to work. You have an electrolytic path through the sea water (through your sea strainer). Ions flow through the water to complete the circuit, that's how stray current corrosion works. Especially in slow moving water. The completed circuit is there.

No, your floating DC ground and no AC to DC grounding connection is not the marine industry standard. I gave a perfect example of how your setup needs only a single fault to have stray current corrosion while the industry standard design usually needs 2 or more faults. You just don't want to admit it.

Show me a European boat with grounding plates that have AC ground and DC negative connected to that. Do you know how many more boats are built in Europe?

Edit: no, there is no path through the seastrainer. Test it.