Do I need an anode?

[Dalliance]

This will seem liek an extremely naive question to most of you but I'm not au fait with 12v marine electrics. I have a newly installed 2 battery 12v system on my boat but no hull anode. The prop is protected by its own anode and the engine has in-built anode on the sea water side. The -ve side of the battery installation appears to be "grounded" to the keel (which is non-encapsulated lead). The boat is 25 years old and I've owned it for 3 years. It didn't have a hull anode at time of purchase and, when I had the new engine and alternator intalled the yard relocated the batteries and re-installed the charging circuit. When the boat is lifted this winter should I have a through hull anode fitted?

 

[fireball]

We don't have a hull anode either ... the prop and shaft is protected by its own anode and the engine has 2 internal ones.
Incidentally, there is no continuity between the -Ve and the shaft/prop ..

None of our seacocks are bonded and are checked annually for de-zincification .. no problems so far ..

btw - we spend the majority of our time on a swinging mooring away from stray currents.

 

[MarkGrubb]

Same here. Hull is GRP (you don't say what you boat is made of which is important) with encapsulated keel so only metal below the water line is shaft/prop, rudder post and skin fittings. No hull anode. The shaft/prop is protected by a collar anode, none of the skin fittings are protected, but I do inspect them. Engine anodes of course.

However, if you have a bolt on keel with metal ballast exposed to the sea water then that may need protecting by an additional anode.

 

[VicS]

The stern gear is protected, if any protection is needed, by its own anode. I assume that's a shaft anode. And the engine will be protected by its own internal anode. Both should be inspected yearly and replaced when necessary.

The lead keel will be ok, the fact that it has survived for 25 years is testimony to that.

Bronze skin fittings should be OK but any that might be brass should be regularly inspected for signs of dezincification. They should not be connected to the same anodes as other items anyway.

The installation of your 12volt system as such should have no relevance but I do not see why it has been connected to the keel. I would not have done that. There may be a path from 12v -ve via the engine, gearbox and stern gear to the water unless it is broken by a flexible coupling.

So no you do not need to fit any hull anodes. What would you be fitting them to protect?

 

[michael_w]

Do you have a P-bracket? So often these are not bonded into the circuit. The normal shaft anode doesn't offer enough protection.

The boat I'm planning to buy needs the P-bracket replaced owing to corrosion. Not a cheap job.

 

[Slow_boat]

My boat is 40yrs old and has never had an anode. There doesn't seem to be any erossion prop, seacocks etc. She has always lived on a drying swinging mooring.

Maybe I should have one.

 

[fireball]

[ QUOTE ]
Maybe I should have one.

[/ QUOTE ]
Definitely - I'd buy the biggest one the chandlery has and put it in the stern locker for safe keeping /forums/images/graemlins/tongue.gif

 

[capnsensible]

Yes. All boats do. If not, sooner or later it will be regretted.

 

[fireball]

[ QUOTE ]
Yes. All boats do. If not, sooner or later it will be regretted.

[/ QUOTE ]
Bowlocks! Not ALL boats do ... and some are worse off if you put them on!

 

[vyv_cox]

Fully agree. There is more male cow manure talked on here about anodes than anything else, for which the previous post by c*pns*ns*bl* is a perfect example.

Anodes are fitted in order to preferentially corrode, thus protecting something higher in the galvanic series that would otherwise corrode. So if nothing is corroding then nothing needs to be protected.

My GRP boat has an anode on the propeller and another on the shaft. Nothing else. I take the earlier point about the P-bracket but it is a difficult shape to protect and my preference is for epoxy coating it as an alternative. My skin fittings, almost certainly brass with a small tin content, have been in service for 22 years with no evident dezincification. What else is corroding?

 

[john_morris_uk]

This isn't true. In fact some wooden boats have expensive damage caused to their strakes by ignorant people fitting anodes that they think 'ought' to be there.

I still have the length of 50 year old mahogony that was destroyed by an anode some prat had bolted through sound timber and ended up destroying it.

 

[VicS]

[ QUOTE ]
However, if you have a bolt on keel with metal ballast exposed to the sea water then that may need protecting by an additional anode.


[/ QUOTE ] While I cannot claim to have studied the chemistry of lead in any great detail I think you will find that although it corrodes quite quickly in soft water containing dissolved air and carbon dioxide (something that makes it unsuitable for use as water pipes in soft-water areas and probably as exposed keels in some rivers and inland lakes) that is prevented by the bicarbonates and sulphates in hard water. Seawater has high concentrations of both.

 

[capnsensible]

mmm. May you always sail and moor nowhere near any other boats. And never visit a marina. Keep your fingers crossed too.

I only base my wild arse guess on many years of living on and working on boats. And replacing anodes that have sacrificed themselves for the noble metals. Doing just what they were designed to do!!

Not qualified really to argue the toss on wooden boats, though I suspect they have metal propellors and stuff. I actually prefer trees...... /forums/images/graemlins/ooo.gif

 

[fireball]

[ QUOTE ]
mmm. May you always sail and moor nowhere near any other boats. And never visit a marina. Keep your fingers crossed too.

[/ QUOTE ]
She's an AWB of around 13 years ... never had a hull anode ... not been a problem so far, don't envisage it being a problem in the future .. however, as with everything - the hull is inspected each year.

Why fix what ain't broke? You weren't an auditor in a previous career were you? "Well... we better check X as that is what we checked last year"

 

[VicS]

[ QUOTE ]
May you always sail and moor nowhere near any other boats. And never visit a marina.

[/ QUOTE ] If you do just don't connect yourself electrically to them for long periods. That's the problem with shore power connections left plugged in all the time in marinas. It creates an electrical connection between all the boats via the earth wire, hence the need for galvanic isolators.

Anodes will corrode if connected to more noble metals, as you say, that's basic electrochemistry at work, but whether the more noble metals actually needed the protection is another matter. Generally bronze fittings should not. In fact one of the MAIB recommendations into the near loss of the fishing vessel "Random Harvest" off Brighton a few years ago (q.v.) was that the skin fittings should be disconnected from the vessels cathodic protection system.

 

[capnsensible]

Nah. Spent sizeable chunks of time maintaining torpedos and torpedo tubes. Along with mucho zinc anodes and various other anti galvanic corrosion devices, some good some not so good. And witnessing high pressure testing of hull valves to ensure no de-aluminification was destroying their integrity.

Also ran a 47 foot Aluminium motor cruiser for a sea school for 2 years. It was a right royal pain trying to stop the thing dissolving!!

Our own boat is a 33 foot Moody. We spent a year in a Spanish marina alongside a steel yacht that managed to leech away a sizeable chunk of our keel!

Hence my remarks. I love a mass debate.

 

[fireball]

[ QUOTE ]
If you do just don't connect yourself electrically to them for long periods. That's the problem with shore power connections left plugged in all the time in marinas. It creates an electrical connection between all the boats via the earth wire, hence the need for galvanic isolators.

[/ QUOTE ]
Unless your shorepower earth isn't connected to any metal part submersed in the water .... in which case you don't need to worry

 

[capnsensible]

Nor any other boat around you!!!!

 

[VicS]

[ QUOTE ]
Unless your shorepower earth isn't connected to any metal part submersed in the water .... in which case you don't need to worry

[/ QUOTE ] It depends on what metal lumps you've got but in most cases it will be if the shore-power installation complies with current recommendations.

 

[john_morris_uk]

[ QUOTE ]
Nah. Spent sizeable chunks of time maintaining torpedos and torpedo tubes. Along with mucho zinc anodes and various other anti galvanic corrosion devices, some good some not so good. And witnessing high pressure testing of hull valves to ensure no de-aluminification was destroying their integrity.

Also ran a 47 foot Aluminium motor cruiser for a sea school for 2 years. It was a right royal pain trying to stop the thing dissolving!!

Our own boat is a 33 foot Moody. We spent a year in a Spanish marina alongside a steel yacht that managed to leech away a sizeable chunk of our keel!

Hence my remarks. I love a mass debate.

[/ QUOTE ]You will also be aware that the corrosion problems of torpedo tubes and aluminium boats are no-where near the same as the possible corrosion problems of bronze seacocks and other fittings which are not connected electrically to anything else and are fittings on a GRP hull .

The original poster asked about whether a hull anode was necessary when there was already an engine anode and a prop anode. I still don't understand why you seem to think that a hull anode is necessary in addition to the cathodic protection he has fitted..

If the boat was to spend some time in a marina plugged into the mains and hence to other boats, then additional precautions might need to be taken. In GRP boats, good quality bronze fittings such as sea-cocks etc, provided that they are not connected electrically with other fittings, survive for many many years without cathodic protection.

If you want the reasons for the strong arguments against putting cathodic protection on the hulls of wooden boats, we will have to discuss it elsewhere.