I trashed five seacocks at sea!

[VicS]

Maybe the anode is there to protect the heat exchanger shell, which seems to be made of some alloy, possibly alu? I theory there should not be any direct contact between stack/endcaps and shell due to the two rubber O-rings..

And presumably the aluminium shell is not in contact with the seawater.

I wonder about the flow erosion,

A characteristic of erosion caused by high or turbulent flow is that the eroded surfaces are left clean and shiny.

I'd think these anodes are decaying quickly because they are surrounded closely by copper alloy components. Dissimilar metals and all that stuff leading to some pretty active galvanic corrosion.

Without knowing what materials are used in the construction it is difficult to know why an anode is fitted. Perhaps the tubes are brass and liable to dezincification ??

 

[Bosun Higgs]

Do you have another wire connecting the engine block to the anode, and the seacocks? If so then any metal parts thus connected and in contact with sea water (internally) will form part of the circuit which zapped your seacocks.
If the engine block is not connected then you should be OK- was this the wire which ended up on the starter positive in error?

No worry. If he has another wire connecting the block to the anode then the 12v positive on the seacocks will turn that anode into a cathode and the dissolved copper / zinc from the seacocks will if near enough be deposited on this. In fact his anode has been eroded which suggests that his anode was also connected to the positive. The fact that his engine started and he didnt have a dead short suggests the block was connected to the battery negative and so would have been the heat exchanger.

Having said all this, currents can flow in funny ways so it is probably sensible to have a quick look at the heat exchanger stack though I would not be having sleepless nights about it.

 

[Haven't-a-Clue]

And presumably the aluminium shell is not in contact with the seawater.

A characteristic of erosion caused by high or turbulent flow is that the eroded surfaces are left clean and shiny.

I'd think these anodes are decaying quickly because they are surrounded closely by copper alloy components. Dissimilar metals and all that stuff leading to some pretty active galvanic corrosion.

Without knowing what materials are used in the construction it is difficult to know why an anode is fitted. Perhaps the tubes are brass and liable to dezincification ??

Fair enough on the erosion front, clean and shiny would be an offence against the Trades Description Act if I claimed it for my anode! As I mentioned earlier, it crumbles into particles about 1-2mm in size and fit perfectly in the tubes! I dunno how Beta do it.

Edit: I think the stack housing, if that's the one the fresh water circulates around, IS aluminium, so I guess that's where the anode is needed. If so, I think the phrase I'm looking for rhymes with "clucking bell".

 

[vyv_cox]

Edit: I think the stack housing, if that's the one the fresh water circulates around, IS aluminium, so I guess that's where the anode is needed. If so, I think the phrase I'm looking for rhymes with "clucking bell".

It would be most unusual to have an anode on thr fresh water side. The antifreeze will protect that.

I was not suggesting that a test anode be made from any old aluminium. I would buy a reasonable sized one, there are plenty of suppliers to pick from, and have several machined from it. There is a specification and several suppliers here.

 

[Haven't-a-Clue]

It would be most unusual to have an anode on thr fresh water side. The antifreeze will protect that.

I was not suggesting that a test anode be made from any old aluminium. I would buy a reasonable sized one, there are plenty of suppliers to pick from, and have several machined from it. There is a specification and several suppliers here.

Sorry Vyv, I guess I'm being ambiguous again. I was under the impression that seawater was able to come into contact with the stack of the heat exchanger inside the alumiuim stack enclosure(?) and that therefore an anode was needed to protect it. If this is not the case, what is the anode protecting? The stack casing (aluminium)? The brass end caps?

Looking at this question, I'm thinking that it, too, is ambiguous

My head hurts, some wine is in order I think.

BTW, thanks for the link. Oh, and apologies for the fred drift to the original poster.

 

[Babylon]

Andy

This makes complete sense to me. I'm due back down to the boat today to check things:

1. Quadruple-check all new seacocks
2. Disconnect seacocks from bonding wire (retain only hull-anode to engine block wire)
3. Check raw-water pump spigot
4. Check heat-exchanger and anode
5. Check insurance excess!

Just spent an afternoon sorting things out.

No problem whatsoever with the pump spigot or the pump itself.

However, the heat-exhanger and the rear cap which contains the anode was plastered with deposits from the now non-existent anode (a total of 28 engine hours since new, of which about 24 hours were with the aforementioned wiring cockup). I managed to scrape most of it off, then disolved the rest in juice from a lemon, before inserting a new anode.

With reference to Haven't-a-Clue's postings above, the Beta engine manual states that this anode needs to be repaced yearly or every 250 hours whichever is the sooner, but that "in some environments" this might need to be done every six months.

 

[Haven't-a-Clue]

Hi Babylon, yeah sorry to drift your thread, glad to hear you've sorted it out. With ref to my posts, I guess the Hamble comes under the "some environments"! and it sure seems like one.

 

[Babylon]

UPDATE - more damage found

Update - more damage to brand new engine parts due to electrolysis appears to have taken place:

* heat-exchanger stack has gone pink, engineer reccomends replacement.
* gearbox (normally bulletproof) is gradually leaking ATF; repair if possible or replacement.

I'm also reliably informed that I'm not the first pillock to have done this...