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Ken Surplice  
#1 Posted : 02 May 2019 21:18:52(UTC)
Rank: Advanced Member

Posts: 224
Location: Basingstoke, Hampshire

Hello Seals,

Can you help me understand the nature of strange corrosion on the inboard side of the posts securing my large hull anode?

The boat: Parker 275 with usual large anode bolted through the hull at the rear

Modification: combined shore power and battery charger professionally fitted, together with galvanic isolator

What I discovered:

1) there are three wires connected to the anode posts inside the hull. Two wires, intact, are on one post. On the other side there is another wire but it has detached from the ring connector.

2) on and around each of the two posts there is a mound of what looks like white curly crystals. If you drilled into a white plastic breadboard, the resulting swarf would resemble the stuff I see on the stainless steel posts that hold the anode. The strange thing is that the stainless steel posts, once the curly powdery stuff is removed, really don't look corroded at all and there is nothing else near the posts that could be depositing crud on them. I did try a cautious lick of some of the powder to see if it was salty but it didn't taste like it.

I have reconnected the detached wire and hope it will stop further corrosion but I am baffled as to where the corrosion had come from. Any ideas?

Thanks - Ken

Ken Surplice
#2 Posted : 08 May 2019 09:01:53(UTC)
Rank: Advanced Member

Posts: 132
Location: Exeter, sober

Hi Ken

My tame electrical engineer is speculating that some damp solution has reached the posts inside the hull and evaporated leaving the crystals there. The posts are just conductors for current through to the anode outside and won’t corrode. Tell us more! Kate

Ken Surplice  
#3 Posted : 09 May 2019 20:19:49(UTC)
Rank: Advanced Member

Posts: 224
Location: Basingstoke, Hampshire

Kate, do thank your tame electrical engineer for this theory. It makes sense to me. I have reconnected the detached wire, cleaned away the mystery material and will observe and report on what happens next.

Thanks - Ken

Ken Surplice
Mike Lockwood  
#4 Posted : 21 May 2019 18:28:32(UTC)
Rank: Advanced Member

Posts: 43


Not sure this is relevant! However, some years ago I had corrosion on the stainless steel upright part of the keel.

I measured the voltage between an over-the-side anode and the top of the keel: 0.5V.

Now, except when sailing, we have a connection between the top of the keel and the over-the-side anode and have had no further problem.

We use a previous year's hull anode.

Mike Lockwood

Lucky Devil

Parker 325/35

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