Anodes who needs 'em!

[Nicholas123]

Well the question is do I need them?

My Macwester 27 has anodes fitted to the bottom leading edge of the keels & the trailing edge but one that is Identical (same mark) that I was looking at yesterday has not.So what is the criteria that causes you to need them?

 

[VicS]

Well the question is do I need them?

My Macwester 27 has anodes fitted to the bottom leading edge of the keels & the trailing edge but one that is Identical (same mark) that I was looking at yesterday has not.So what is the criteria that causes you to need them?

Corrosion !

If an identical boat does not have anodes and shows no signs of excessive corrosion then it is unlikely that you boat needs them.

I'd guess that when the Macwester 27 was built anodes on boats were relatively uncommon, available perhaps as "extras"

They have become fashionable, the people who make and sell them of course recommend them and many people fit and renew them regularly purely as a precautionary measure.

Commonly they are fitted, whether necessary or not, to protect props.

They are necessary to protect things like saildrives and it seems some of the very expensive folding propellers despite the fact that the latter are often made of some of the most corrosion resistant alloys available.

 

[Robert Wilson]

Your response stating "fitted whether necessary or not etc" seems to "fly in the face" of ALL the written wisdom of the last year in yachting/boating press.
My old boat (Javelin 30 circa 1982) has a string of wires throughout the hull connecting annodes and seacocks/engine etc.
Do you think I need the protection?
I replaced two prop-shaft annodes as usual this Spring, which have dropped off somewhere (first time that's happened). Small barnacles have started to grow on the shaft but no other outward sign of "attack/corrosion". Said barnacles removed.
My main external annode is still in pretty good shape, but I'm now wondering whether I need to spend the considerable money during annual haul-out/winterisation to replace any or all of them.
Any advice would be most appreciated. Thanks

 

[V1701]

My anode (large pear drop shaped one at the back near the prop/shaft & appropriately bonded to my knowledge) is a year and a bit old and looks like new after cleaning it and the rest of the undersides off last week (with the boat still in the water). Boat lives in a large marina, no corrosion anywhere & I'm a bit confused as to why there is no wear on the anode whatsoever...

 

[Nicholas123]

Corrosion !

If an identical boat does not have anodes and shows no signs of excessive corrosion then it is unlikely that you boat needs them.

I'd guess that when the Macwester 27 was built anodes on boats were relatively uncommon, available perhaps as "extras"

They have become fashionable, the people who make and sell them of course recommend them and many people fit and renew them regularly purely as a precautionary measure.

Commonly they are fitted, whether necessary or not, to protect props.

They are necessary to protect things like saildrives and it seems some of the very expensive folding propellers despite the fact that the latter are often made of some of the most corrosion resistant alloys available.

I took a close look at the keels on the one I saw down the hard yesterday Vic & I could'nt see any sign of visible corrosion but maybe the stainless steel keelbolts deep inside the iron are wasting away? Talk of crevice corrosion has put the frighteners on me.
A thorough understanding of the principles involved would be beneficial.

PS:It was the horror at drawing out an iron keelbolt on my last boat that had wasted away to nothing in a few years that caused me to get rid of it (no anodes anywhere) so I am going to take this subject seriously now.

 

[Robin]

In the UK we had a large pear shaped anode wired to the engine and therefore connected to the prop via gearbox and shaft, we replaced this annually although it would probably have lasted 2 years. We also had a small cone anode on the Brunton prop on our last UK boat, replaced annually, but no shaft anodes. Cost of prop about £1800, cost of anodes about £25, no -brainer decision IMO. Nothing else was bonded to the anode such as seacocks etc.

Over here in the USA, EVERYTHING is bonded, such as all thru=hulls, strainers, rudder shafts, P-Bracket struts etc, plus (this one is a mobo) we have anodes on both trim tabs, both rudders two shaft anodes on each shaft and a large plate anode on the transom underwater area, everything metal in contact with the water is wired to an anode or has one attached. In our home marina, divers clean bottoms, check and replace anodes for owners and some boats in some parts of the marina get through anodes in 2 months, our dock is known to be electrically 'hot', in as much as we are amongst a lot of big boats continuously running aircons (including us) and it only takes one bad connection to leak stray current (110V doesn't help as the amps are higher). Last week a diver got a flash bang shock from the aircon water intake of a sailing boat three berths away from us, which prompted me to have our anodes checked even though we have been afloat just 3 months from replacing them all, we were OK, better than 80% good but we have a galvanic isolator installed which should help protect us. The USA system is different, they bond everything, the UK side of the pond bonds just the prop and maybe P-struts.

That is the extent of my knowledge but in the OP's shoes I would fit anodes to protect the prop but not bother on the keels.

 

[Robert Wilson]

A little knowledge is a dangerous thing - I once heard. On the other hand "An expert is either a Drip Under Pressure (ex-spert) or Someone Brought In At The Last Minute To Take/Share/Make BLAME"
I assume that because my annodes are wasting away then they are "Working" at something.
To ASSUME is to make an "ASS" out of "ME", in crossword parlance.
I know we caould all worry ourselves to death about every little thing, but I'd really like to keep my sailing costs down and at the same time keep my survival chances up.
So, anybody got any other ideason this subject?

 

[ghostlymoron]

If you spend most of your time on a remote mooring or anchorage, you are unlikely to have your metal bits suffering from electrolytic corrosion. But in most marinas there are often stray voltages kicking about so sacrificial anodes are more likely to be of use.
If you observe no wastage on your anode, it's not doing anything and should last for several years. The general advice is to replace when its 50% wasted but if the annual rate is slow, you could probably stretch it to 75%.

 

[rotrax]

Our boat is American, and as has been said before, all seacocks, engine etc are grounded and linked. We have no anodes, but a Galvanic Isolator is standard eqipment. She has been out of the water four times in three years and no-repeat no-corrosion has been spotted. I do know what to look for as well-our previous boat had had the P bracket dissapear due to galvanic corrosion. In a previous life, I worked for Kawasaki Motors UK Ltd. in the technical department. Some models were suffering from severe internal corrosion of the exhaust systems. They sent a guy from HQ in Japan to come and sort it. His name was Harry Koroda. We did laugh............

 

[VicS]

Your response stating "fitted whether necessary or not etc" seems to "fly in the face" of ALL the written wisdom of the last year in yachting/boating press.
My old boat (Javelin 30 circa 1982) has a string of wires throughout the hull connecting annodes and seacocks/engine etc.
Do you think I need the protection?
I replaced two prop-shaft annodes as usual this Spring, which have dropped off somewhere (first time that's happened). Small barnacles have started to grow on the shaft but no other outward sign of "attack/corrosion". Said barnacles removed.
My main external annode is still in pretty good shape, but I'm now wondering whether I need to spend the considerable money during annual haul-out/winterisation to replace any or all of them.
Any advice would be most appreciated. Thanks

Sorry but it is impossible to say from here to what extent your cathodic protection system is necessary but I'd think from what you say much of it , if not all of it, is unnecessary or inadvisable.

A "string of wires thoroughout the hull" connecting anodes seacocks engine etc is a pretty bad staring point.

Seacocks and other through hulls should be of a corrosion resistant material which does not need cathodic protection. It is now considered bad practice to connect them to the anodes ( One of the recommendations in the MAIB report (q.v) into the near loss of the F.V Random Harvest a few years ago)

The connection to the engine will be to establish a path between the hull anode and the stern gear for its protection ( it has nothing to do with protecting the engine itself). To complete the connection any flexible coupling must of course be bridged.

The shaft anodes also protect the stern gear. A shaft anode and a hull anode connected via the engine is a belt and braces arrangement.

A good bronze prop on a stainless steel shaft may well not require protection at all hence my comment "fitted whether necessary or not etc"
The Westerly I crewed for many years has no anodes at all. Despite now being about 36 years old it still has its original prop and shaft with no signs of corrosion. All the seacocks and skin fittings are also original. There is no excessive corrosion of the cast iron keels either.

 

[VicS]

My anode (large pear drop shaped one at the back near the prop/shaft & appropriately bonded to my knowledge) is a year and a bit old and looks like new after cleaning it and the rest of the undersides off last week (with the boat still in the water). Boat lives in a large marina, no corrosion anywhere & I'm a bit confused as to why there is no wear on the anode whatsoever...

If there is no loss of metal from the anode at all I would suspect the bonding is not as good as you believe. However if that is so and there is no corrosion of the items it is supposed to be bonded to then it suggests also that it is not necessary.

The big danger in marinas comes from shorepower supplies left connected ( connected, not necessarily in use). The earth should be connected to the DC negative I except with isolated Dc systems) and the boats internal earth sytem which will include the anodes. All the while the shorepower is plugged in there is a connection from the anodes to the marina structure and to other boats wich are also plugged in. Galvanic corrosion can then led to rapid loss of metal from the anodes.
Fitting a Galvanic isolator is the means of preventing this.

 

[macd]

Some models were suffering from severe internal corrosion of the exhaust systems. They sent a guy from HQ in Japan to come and sort it. His name was Harry Koroda. We did laugh............

Trust you kept Koroda-san away from your car.

Were the exhausts the ones with a stainless header welded to a mild steel collector (if I remember correctly). Always thought that a bit dodgy.

 

[VicS]

In the UK we had a large pear shaped anode wired to the engine and therefore connected to the prop via gearbox and shaft, we replaced this annually although it would probably have lasted 2 years. We also had a small cone anode on the Brunton prop on our last UK boat, replaced annually, but no shaft anodes. Cost of prop about £1800, cost of anodes about £25, no -brainer decision IMO. Nothing else was bonded to the anode such as seacocks etc.

Over here in the USA, EVERYTHING is bonded, such as all thru=hulls, strainers, rudder shafts, P-Bracket struts etc, plus (this one is a mobo) we have anodes on both trim tabs, both rudders two shaft anodes on each shaft and a large plate anode on the transom underwater area, everything metal in contact with the water is wired to an anode or has one attached. In our home marina, divers clean bottoms, check and replace anodes for owners and some boats in some parts of the marina get through anodes in 2 months, our dock is known to be electrically 'hot', in as much as we are amongst a lot of big boats continuously running aircons (including us) and it only takes one bad connection to leak stray current (110V doesn't help as the amps are higher). Last week a diver got a flash bang shock from the aircon water intake of a sailing boat three berths away from us, which prompted me to have our anodes checked even though we have been afloat just 3 months from replacing them all, we were OK, better than 80% good but we have a galvanic isolator installed which should help protect us. The USA system is different, they bond everything, the UK side of the pond bonds just the prop and maybe P-struts.

That is the extent of my knowledge but in the OP's shoes I would fit anodes to protect the prop but not bother on the keels.

There can be no defence of dangerous situations that result in divers , or anyone else, receiving electric shocks from defectively wired boats. Given what you say about the marina being "hot" it is surprising that diving ( or swimming) is allowed in the marina.

Your galvanic isolator will only protect your boat from corrosion due to very low voltages arising from dissimilar metals etc . It will not offer any protection from faults on the 110 volt AC power systems. A galvanic isolator is designed in fact not to block current from such sources so that the safety aspects of the earthing /grounding system is not affected. They will not even block current arising from faults on 12 or 24 volt DC systems.

 

[cimo]

Well the question is do I need them?

My Macwester 27 has anodes fitted to the bottom leading edge of the keels & the trailing edge but one that is Identical (same mark) that I was looking at yesterday has not.So what is the criteria that causes you to need them?

perhaps worthwhile posting this on the macwester site also Nicholas http://www.macwester.org/.

My atlanta has encapsulated keels - so no comparison here.

My rudder & skeg bracket are well pitted though (single 1.5kg anode attached to the rudder - it's obvious from my anode wear that the anode is required here.) - so perhaps of some relevance to you.

(I have since epoxied the rudder, to buy a few years - & I now fit 2 anodes, one either side of the rudder. It often comes down to a case of suck n' see).

 

[Robin]

There can be no defence of dangerous situations that result in divers , or anyone else, receiving electric shocks from defectively wired boats. Given what you say about the marina being "hot" it is surprising that diving ( or swimming) is allowed in the marina.

Your galvanic isolator will only protect your boat from corrosion due to very low voltages arising from dissimilar metals etc . It will not offer any protection from faults on the 110 volt AC power systems. A galvanic isolator is designed in fact not to block current from such sources so that the safety aspects of the earthing /grounding system is not affected. They will not even block current arising from faults on 12 or 24 volt DC systems.

Diving is a continuous Forth Bridge operation here, with brackish water, high temperatures, to keep boats clean and make money for the divers. All the boats leave their aircons running 24/7 (on 110VAC) even if not on board, to prevent mould I was told, we live on ours and have three aircons running but from one 110VAC pump. One of the primary diver jobs I was told is cleaning the outside hull strainers for the aircon water pumps, because if the flow slows the efficiency drops dramatically. The offending boat in the shock incident is now disconnected and the diver now answers to 'sparky'. The whole 110VAC setup is alien to me, since in our case we have two 30A cords running from a Y-splitter plugged into a 208V 50A connector, which i think is obtained from 415V 3-phase fed round the marina (cheaper than running 110V?) Personally I don't fancy swimming in here, we see mannitees which are fairly cuddly, big tarpon (6-8ft long) which I suppose are harmless but then there was a dead alligator just up the road, run over by a car... On that basis I'll pay a diver!

 

[V1701]

If there is no loss of metal from the anode at all I would suspect the bonding is not as good as you believe. However if that is so and there is no corrosion of the items it is supposed to be bonded to then it suggests also that it is not necessary.

The big danger in marinas comes from shorepower supplies left connected ( connected, not necessarily in use). The earth should be connected to the DC negative I except with isolated Dc systems) and the boats internal earth sytem which will include the anodes. All the while the shorepower is plugged in there is a connection from the anodes to the marina structure and to other boats wich are also plugged in. Galvanic corrosion can then led to rapid loss of metal from the anodes.
Fitting a Galvanic isolator is the means of preventing this.

Thanks Vic, I'll start with checking the bonding...

 

[rob2]

Anodes offer protection by effectively directing a current between it and the item to be protected, much the same mechanism as the electrolyte between the plates in a wet cell battery. The process works primarily between surfaces in line-of-sight and reasonable proximity. For this reason, most through hull fittings which are not close enough to other materials or the anode to be affected do not need bonding. Many iron keels are not protected by anodes as they do not have any dissimilar metals close by to react with and any corrosion will be spread over such a wide surface area. I presume the reason that iron rudders tend to have anodes is their proximity to the sterngear and maybe the metallurgy of their pintles and gudgeons. Keel bolts will not be protected by anodes as they are hidden from them, although if there is a weep of seater into them, then they can suffer from crevice corrosion - aggravated by the lack of oxygen around them.

After all that, it will serve me right when my folding prop drops a blade - anode or no!

Rob.

 

[ex-Gladys]

Lack of a shaft anode forced me to have to buy a new prop a few years ago.. as someone else has said, 25 quid for an anode every two years or 300 for a prop.... No Brainer. The prop had de zinced bigtime

 

[Nicholas123]

If you spend most of your time on a remote mooring or anchorage, you are unlikely to have your metal bits suffering from electrolytic corrosion. But in most marinas there are often stray voltages kicking about so sacrificial anodes are more likely to be of use.
If you observe no wastage on your anode, it's not doing anything and should last for several years. The general advice is to replace when its 50% wasted but if the annual rate is slow, you could probably stretch it to 75%.

My last boat was moored on a remote mooring & the keel bolt I drew out went from over an inch diameter down to nothing in less than ten years.I don't know if that was electrolytic action but it sure as hell was alarming.(I had had the keel off 7/8 years previously so was able to check the condition.When I went to nip up the keel bolts last year as a matter of routine.The spanner just revolved at the slightest pressure & I drew out the stub about 4" long)

 

[Nicholas123]

perhaps worthwhile posting this on the macwester site also Nicholas http://www.macwester.org/.

My atlanta has encapsulated keels - so no comparison here.

My rudder & skeg bracket are well pitted though (single 1.5kg anode attached to the rudder - it's obvious from my anode wear that the anode is required here.) - so perhaps of some relevance to you.

(I have since epoxied the rudder, to buy a few years - & I now fit 2 anodes, one either side of the rudder. It often comes down to a case of suck n' see).

Thanks for the suggestion but I'm not very well off & the idea of joining a club with Commodores & Vice Commodores makes me feel slightly uncomfortable.
That's a bit odd that you are having so much trouble with your rudder brackets because that's something that never gave me a moments concern.Maybe it's because mine were stainless steel & yours ar'nt?