SimbaDog
Well-Known Member
See quite a few around in marina's. do they do anything?
If so how are they wired in?
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If so how are they wired in?
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Hanging anode
- Thread starter SimbaDog
- Start date
Richard10002
Well-Known Member
And are they really £160 or so, (Mailspeed Marine)
Evadne
Well-Known Member
I think if you've got a problem that wastes your hull anodes rapidly, such as an earthing problem with a mains wire left plugged in, then you can monitor it with a dunking anode that you check every time you go sailing.
You would run a wire from a unit that is bonded into the hull anodes.
You would run a wire from a unit that is bonded into the hull anodes.
wotayottie
Well-Known Member
most boats seem to have the battery negative wired to the anode under the boat, so wiring in a second anode would only need you to pick up the spare power socket in the cockpit . Might not even need to switch the socket on if the switching is in the positive side of the circuit.
Thats said, the resistance in the wiring from the anode to whatever you are wanting to protect need to be as low as possible, so spindly bell wire wont help effectiveness. For the same reason, dont dangle the anode over the bow and expect it to do much for your stern gear.
Ther usually are lots of old discarded half used zinc anodes lying around boatyards. Why not attach a couple to a decent wire and use that instead.
Thats said, the resistance in the wiring from the anode to whatever you are wanting to protect need to be as low as possible, so spindly bell wire wont help effectiveness. For the same reason, dont dangle the anode over the bow and expect it to do much for your stern gear.
Ther usually are lots of old discarded half used zinc anodes lying around boatyards. Why not attach a couple to a decent wire and use that instead.
charles_reed
Well-Known Member
really only necessary for aluminium boats, when they're just attached to the hull.
If you want to fit one for street cred (which is probably the reason the ones you've seen are fitted) attach it to your anode ground circuit, sometimes combined with RF ground.
Just attaching it to the engine probably just makes the fizzy bits of the boat fizz faster.
If you want to fit one for street cred (which is probably the reason the ones you've seen are fitted) attach it to your anode ground circuit, sometimes combined with RF ground.
Just attaching it to the engine probably just makes the fizzy bits of the boat fizz faster.
charles_reed
Well-Known Member
well Richard
there are always mugs around to buy snake oil
there are always mugs around to buy snake oil
Quandary
Well-Known Member
As someone who has used hanging anodes for 15 odd years (in combination with shaft anodes) I would be really interested in the science that your response is based on, with particular reference to the errors that companies like M.G. Duff are making in the advice they have been publishing.
A response is much better understood if it is combined with some explanation, so if you have the time some elaboration of the physics would be really welcome!
A response is much better understood if it is combined with some explanation, so if you have the time some elaboration of the physics would be really welcome!
samwise
Well-Known Member
I was advised to use galvanised wire for the hanging anode. I made one up for short term use when we came back from the Med via the canals and our zinc anodes passivated i.e. became coated with a white powder that reduces efficiency. The fresh water anode I fitted before we started up the Rhone has dissolved away completely shortly after reaching the salt stuffI I made up my hangover anode by attaching a shaft anode to the galvanised cable and hooking it up to battery negative. It cost nothing like £120 certainly less than £20. MG Duff were very helpful.
When we hauled the boat last year, I ground off the deposit on the zinc anodes and they will do another season.
When we hauled the boat last year, I ground off the deposit on the zinc anodes and they will do another season.
charles_reed
Well-Known Member
I am sorry my gibe about street-cred caused you so much angst.
As someone who uses shaft, prop, 2 rudder-stock, main, and two beaching stub anodes I fail to see how I contradict M G Duff on any points of my brief post and also how a hanging anode benefits a GRP boat with full anodic protection.
As to an explanation of the physics I'm sure you're totally familiar with the theory of galvanic couples, bonding and the importance of not bonding dissimilar materials together.
Perhaps you'd like to extol the benefits of a hanging anode from your position of anonymity.
As someone who uses shaft, prop, 2 rudder-stock, main, and two beaching stub anodes I fail to see how I contradict M G Duff on any points of my brief post and also how a hanging anode benefits a GRP boat with full anodic protection.
As to an explanation of the physics I'm sure you're totally familiar with the theory of galvanic couples, bonding and the importance of not bonding dissimilar materials together.
Perhaps you'd like to extol the benefits of a hanging anode from your position of anonymity.
VicS
Well-Known Member
A hanging anode must be hanging close to the item it is intended to protect. Easy to get it close to stern drives on motor boats and stern gear on some saily boats but not so easy it get them close to sail drives.
They must also be bonded to the item being protected. Connection to the negative connection of a deck socket probably not the best of ideas.
People with particularly vulnerable bits like stern drives like them because they can maintain protection if the fitted anodes waste away between inspections.
Aluminium hull owners also like them!
They must also be bonded to the item being protected. Connection to the negative connection of a deck socket probably not the best of ideas.
People with particularly vulnerable bits like stern drives like them because they can maintain protection if the fitted anodes waste away between inspections.
Aluminium hull owners also like them!
Quandary
Well-Known Member
Touchy; Moi?
For myself, I am interested in understanding this subject, that is why I chose to read the replies to this particular post. I still don't fully understand the differing rates of corrosion that occur in apparently similar circumstances and a hanging anode is attractive because it can be inspected regularly and cleaned regularly of muck and passivated coating, when folding props are costing over £1k a time to replace. I formerly used to use two shaft anodes as one was usually still there at lift out.
My boat currently spends long periods in fresh water but too long in the sea to use magnesium, aluminium anodes are not made for it and now with a bronze three blade folder (fantastic prop.) on an alloy saildrive I am searching for answers. The problem is exacerbated because the anodes on the prop. are so small and shortlived and I would like to be able to go on to an 18 month in, 6 month out cycle. Any response from anyone who understands and can really explain the subject will be gratefully received.
For myself, I am interested in understanding this subject, that is why I chose to read the replies to this particular post. I still don't fully understand the differing rates of corrosion that occur in apparently similar circumstances and a hanging anode is attractive because it can be inspected regularly and cleaned regularly of muck and passivated coating, when folding props are costing over £1k a time to replace. I formerly used to use two shaft anodes as one was usually still there at lift out.
My boat currently spends long periods in fresh water but too long in the sea to use magnesium, aluminium anodes are not made for it and now with a bronze three blade folder (fantastic prop.) on an alloy saildrive I am searching for answers. The problem is exacerbated because the anodes on the prop. are so small and shortlived and I would like to be able to go on to an 18 month in, 6 month out cycle. Any response from anyone who understands and can really explain the subject will be gratefully received.
grumpy_o_g
Well-Known Member
Brunton have come up with a through-hull anode that can be checked or replaced with lifting the boat - Click
There's two threats - electrolytic and galvanic corrosion. The write-up below is pretty much what I wrote for the BKYC about 30 years ago assuming I've managed to read my writing correctly after all that time (I added a bit in the middle). I'd be interested to hear any comments or any errors I've made from the knowledgeable on the forum, especially on the assumptions on voltages expected which I based on something I found in a flying boat AP!!
Electrolysis is basically electro-plating, just like EPNS or gold plating, etc. It's far more damaging than galvanic corrosion and this is the one that can eat anodes or even props in a matter of weeks in extremes. Electrolysis takes place between two metals but there has to be a potential difference between them in the first place. In simplistic terms the water is completing a circuit and the metal transferred between the anode and cathode is the direct result of current flowing. Remember that the anodes are there to make a more attractive target for the electrolysis than whatever you're trying to protect so the first step should be to reduce or eliminate the initial problem rather than introduce a "decoy" for the electrolytic reaction. This is where bonding is critical. If there is a very, very low resistance connection between all the submersed and dissimilar metal components on your boat electrolysis won't occur. The down-side is that, if your excellent bonding is all that is stopping it happening, then an unnoticed break in the bonding could lead to a sudden onset of severe electrolysis. The best bet is to not only make sure that your bonding is very good (the connections are usually the weak links, not the cables) but also to break the bonding every so often and put a Fluke or other high-quality multi-meter between the bonding cable and the connection. Any voltage is undesirable but it may be impossible to get it below 100mV or so. If it's much above 1/2 Volt start looking for the reason and fix it.
An isolation transformer sits between the shore power supply of the marina and boats circuit. A feature of this type transformer is that will only pass an alternating current (such as 240V AC mains). It will not allow a direct current to pass so it is impossible to create a steady potential difference between the marina an your boat. It will not protect against galvanic corrosion despite people referring to these as Galvanic Isolators. The "standing voltage" on a company power line between neutral and earth can be very high so never bond your shore power neutral to earth (in fact don't do it at home either). I suspect that disconnecting shore power when leaving the boat would solve many problems - putting the boat on swinging mooring away from stray currents would solve most of the rest.
Galvanic corrosion is slightly different and does not require a potential difference between the two items. Actually the opposite is true and it will create a potential difference between the two items as the metal flows from one item to the other. Effectively you've built a battery with, for example, your prop and a through-hull fitting that is made of a poor quality alloy that has zinc in it as the terminals. Apart from making sure that you only fit metals that will not cause a problem, not only with your boat but also with any other boats or anything in the water nearby, the only thing you can do is fit a sacrificial anode that will be "eaten" before the rest of your boat.
The sacrificial anode will also protect against electrolytic corrosion so it's essential it is properly bonded too or you will lose the anode virtually overnight. Obviously the anode, usually a lump of zinc, aluminium or magnesium, will gradually disappear anyway and will need replacing. If it needs replacing significantly faster than other boats nearby it is worth investigating as you may have a problem - if nothing else they may be better bonded so it is worth checking yours.
The question of whether or not to bond the negative terminal of the battery to the rest of the bonding is open to debate. Many insist it is essential but I am not sure it has any significant advantages. It also opens the way for a short circuit across the battery between any bonded object and any live cable.
Note that the above is true for fibre-glass boats and by and large the wooden boats too. Steel hulls are a different matter and, if anyone has an aluminium hull, they're probably already an expert (if not they soon will be!!).
Actually I've just found quite good summary here - Click here
There's two threats - electrolytic and galvanic corrosion. The write-up below is pretty much what I wrote for the BKYC about 30 years ago assuming I've managed to read my writing correctly after all that time (I added a bit in the middle). I'd be interested to hear any comments or any errors I've made from the knowledgeable on the forum, especially on the assumptions on voltages expected which I based on something I found in a flying boat AP!!
Electrolysis is basically electro-plating, just like EPNS or gold plating, etc. It's far more damaging than galvanic corrosion and this is the one that can eat anodes or even props in a matter of weeks in extremes. Electrolysis takes place between two metals but there has to be a potential difference between them in the first place. In simplistic terms the water is completing a circuit and the metal transferred between the anode and cathode is the direct result of current flowing. Remember that the anodes are there to make a more attractive target for the electrolysis than whatever you're trying to protect so the first step should be to reduce or eliminate the initial problem rather than introduce a "decoy" for the electrolytic reaction. This is where bonding is critical. If there is a very, very low resistance connection between all the submersed and dissimilar metal components on your boat electrolysis won't occur. The down-side is that, if your excellent bonding is all that is stopping it happening, then an unnoticed break in the bonding could lead to a sudden onset of severe electrolysis. The best bet is to not only make sure that your bonding is very good (the connections are usually the weak links, not the cables) but also to break the bonding every so often and put a Fluke or other high-quality multi-meter between the bonding cable and the connection. Any voltage is undesirable but it may be impossible to get it below 100mV or so. If it's much above 1/2 Volt start looking for the reason and fix it.
An isolation transformer sits between the shore power supply of the marina and boats circuit. A feature of this type transformer is that will only pass an alternating current (such as 240V AC mains). It will not allow a direct current to pass so it is impossible to create a steady potential difference between the marina an your boat. It will not protect against galvanic corrosion despite people referring to these as Galvanic Isolators. The "standing voltage" on a company power line between neutral and earth can be very high so never bond your shore power neutral to earth (in fact don't do it at home either). I suspect that disconnecting shore power when leaving the boat would solve many problems - putting the boat on swinging mooring away from stray currents would solve most of the rest.
Galvanic corrosion is slightly different and does not require a potential difference between the two items. Actually the opposite is true and it will create a potential difference between the two items as the metal flows from one item to the other. Effectively you've built a battery with, for example, your prop and a through-hull fitting that is made of a poor quality alloy that has zinc in it as the terminals. Apart from making sure that you only fit metals that will not cause a problem, not only with your boat but also with any other boats or anything in the water nearby, the only thing you can do is fit a sacrificial anode that will be "eaten" before the rest of your boat.
The sacrificial anode will also protect against electrolytic corrosion so it's essential it is properly bonded too or you will lose the anode virtually overnight. Obviously the anode, usually a lump of zinc, aluminium or magnesium, will gradually disappear anyway and will need replacing. If it needs replacing significantly faster than other boats nearby it is worth investigating as you may have a problem - if nothing else they may be better bonded so it is worth checking yours.
The question of whether or not to bond the negative terminal of the battery to the rest of the bonding is open to debate. Many insist it is essential but I am not sure it has any significant advantages. It also opens the way for a short circuit across the battery between any bonded object and any live cable.
Note that the above is true for fibre-glass boats and by and large the wooden boats too. Steel hulls are a different matter and, if anyone has an aluminium hull, they're probably already an expert (if not they soon will be!!).
Actually I've just found quite good summary here - Click here
Allan
Well-Known Member
My boat is moored in fresh water (Cardiff bay)and sailed in salt water. I will be changing the Zinc anode for an Aluminium one and buying a magnesium hanging block for hanging while on the mooring. The exsisting one covered in corosion so something needs doing. Luckily I am able to dry out regularly to check the condition and see if I have made the right choice.
Allan
Allan
VicS
Well-Known Member
[ QUOTE ]
My boat is moored in fresh water (Cardiff bay)and sailed in salt water
[/ QUOTE ] The trouble is going to be that while in fresh water that zinc or aluminium anodes become passivated in time and are not effective even when retuned to salt water unless cleaned off.
Goodness knows what the answer is, obviously not possible to clean them off every time you use the boat. Use it frequently I guess.
My boat is moored in fresh water (Cardiff bay)and sailed in salt water
[/ QUOTE ] The trouble is going to be that while in fresh water that zinc or aluminium anodes become passivated in time and are not effective even when retuned to salt water unless cleaned off.
Goodness knows what the answer is, obviously not possible to clean them off every time you use the boat. Use it frequently I guess.
Allan
Well-Known Member
When I spoke to McDuff they basically said the same. They said there can also be problems with one anode making the other degrade faster. After all my research, I think there is no "correct" answer. I will keep a wire brush handy and give the hull anode a clean everytime I dry out. Using the boat as frequently as I do should help, also there is no power on our pontoon.
Allan
Allan
charles_reed
Well-Known Member
I'd agree that a hanging anode, on a boat that spends much time moored is an attractive idea, but the problem comes in trying to bond it effectively to the item you're trying to protect.
My daughter, worked for a time with the "authority" in the UK on galvanic corrosion (she's a prof in Southampton Uni School of Engg) and my attempts to cross-examine him on the subject led me to believe the subject to be more of a black-art than I'd assumed. I just hope my questioning didn't drive the poor chap into his subsequent resignation.
My prop has al-bronze blades - quite low on the table, and I had a gold-plated RF ground-plane, quite close to it. Shaft anodes were disappearing in about 6-months, despite the main anode being bonded to tube and shaft (306 SS is not a good conductor), but the boss anode was lasting quite well. I finally cured it by fitting two 70mm flat anodes in the beaching leg just underneath the prop and another 2 100mm anodes on the stainless rudder stock (that also reduced corrosion on the lower pintle-bracket fixings).
My conclusions are that there are so many variables in each of these mini-cells that hoping one anode, however well bonded, will do the job is rather whistling in the dark.
Fix an anode directly to any pieces you want to protect, is the only safe way to defeat corrosion. If anything M G Duff are proposing too small a X section bonding wire IMHO.
In your case Al anodes are the theoretical answer, in brackish or fresh water zinc passivates in no time at all, I've even found mine getting covered after a period of heavy rain in sea-moorings. (That's the advantage of anodes in plain view).
If there aren't any made to fit your particular mounting, I'd suggest doing what I have to do, take an angle-grinder to the nearest size - at least Al isn't as noxious as zinc to work on.
Another tip - buy anodes from a fisherman's coop, not chandleries or even M G Duff (who do produce quality ones). You'll find a much larger range of sizes and all at about 20% of the prices of yottie ones. Though I can't say I've seen Al anodes in a fishermans' Co-op, but then I wasn't looking. If you're in UK with it's nearly moribund fishing industry, I'll acknowledge it's a problem trying to find them but there's lots in Bretagne and Spain.
If you have a Volvo saildrive, you've my sincere sympathy - the mix of metals in them is horrific and I don't know what to suggest to counter it. I suppose the hanging anode is the only approximate answer, bonded straight to the saildrive leg, but I can't see that doing much for the prop, unless you can get the anode about 100mm away.
As for cycles - ring prop anode about 12-months, plate and boss anodes about 2 years and main anode about 5 years (but that's a massive 4.5kg one). Boat out of water about 2/12 months.
No math or physics there, because I don't think there's an accurate model from which to derive anything.
Is your boat, by any chance, off an old mining drain-off? A totally different set than appears to rule because of all the stray metallic ions around - that's wher the teal esoteris begins and I won't pontificate...
My daughter, worked for a time with the "authority" in the UK on galvanic corrosion (she's a prof in Southampton Uni School of Engg) and my attempts to cross-examine him on the subject led me to believe the subject to be more of a black-art than I'd assumed. I just hope my questioning didn't drive the poor chap into his subsequent resignation.
My prop has al-bronze blades - quite low on the table, and I had a gold-plated RF ground-plane, quite close to it. Shaft anodes were disappearing in about 6-months, despite the main anode being bonded to tube and shaft (306 SS is not a good conductor), but the boss anode was lasting quite well. I finally cured it by fitting two 70mm flat anodes in the beaching leg just underneath the prop and another 2 100mm anodes on the stainless rudder stock (that also reduced corrosion on the lower pintle-bracket fixings).
My conclusions are that there are so many variables in each of these mini-cells that hoping one anode, however well bonded, will do the job is rather whistling in the dark.
Fix an anode directly to any pieces you want to protect, is the only safe way to defeat corrosion. If anything M G Duff are proposing too small a X section bonding wire IMHO.
In your case Al anodes are the theoretical answer, in brackish or fresh water zinc passivates in no time at all, I've even found mine getting covered after a period of heavy rain in sea-moorings. (That's the advantage of anodes in plain view).
If there aren't any made to fit your particular mounting, I'd suggest doing what I have to do, take an angle-grinder to the nearest size - at least Al isn't as noxious as zinc to work on.
Another tip - buy anodes from a fisherman's coop, not chandleries or even M G Duff (who do produce quality ones). You'll find a much larger range of sizes and all at about 20% of the prices of yottie ones. Though I can't say I've seen Al anodes in a fishermans' Co-op, but then I wasn't looking. If you're in UK with it's nearly moribund fishing industry, I'll acknowledge it's a problem trying to find them but there's lots in Bretagne and Spain.
If you have a Volvo saildrive, you've my sincere sympathy - the mix of metals in them is horrific and I don't know what to suggest to counter it. I suppose the hanging anode is the only approximate answer, bonded straight to the saildrive leg, but I can't see that doing much for the prop, unless you can get the anode about 100mm away.
As for cycles - ring prop anode about 12-months, plate and boss anodes about 2 years and main anode about 5 years (but that's a massive 4.5kg one). Boat out of water about 2/12 months.
No math or physics there, because I don't think there's an accurate model from which to derive anything.
Is your boat, by any chance, off an old mining drain-off? A totally different set than appears to rule because of all the stray metallic ions around - that's wher the teal esoteris begins and I won't pontificate...
Allan
Well-Known Member
When I first read your post I thought it was aimed at me, it seems very helpfull, thank-you. I think my plan, above, is the one one I will stick with for now. Cardiff bay is fed by the rivers Taff and Ely, as they both come from the Welsh valleys I think they may included mine run off. I would be interested to hear if you think my plan is suitable. Before I bought the boat it was fitted with a zinc anode and was moored in the tidal part of the river Frome towards Wareham (Ridge wharf).
Allan
Allan
Quandary
Well-Known Member
I appreciate the information posted, particularly the explanatory posts above which are relevant to my problem and hopefully will help devise some sort of solution. I intend to take time to read them again for it is along long time since I was in a physics classroom. Thank you.
I suspect that part of my problem is my one design racing background where everything had to be ultra smooth and we used to burnish the antifouling. One of the Sigmas I purchased came from Burnham on Crouch and had a massive hull anode on two stout bolts, of course we had to take this off and fair everything if we were to be competitive!!! To compensate I hung it over the side of the cockpit with a heavy copper cable bonded to the circuit which connected all the skin fittings and while it eroded steadily over the years the shaft anodes degraded slowly and the prop etc. stayed in good condition for the seven years I kept the boat. However in those days the boat was in sea water most of the time. My current boat has a Volvo saildrive This is the first time I have ever had one of these with all the problems described above and it is only now that I have begun to think through the problem. (It is difficult to find an affordable Scandanavian performance boat that has shaft drive.) I believe aluminium anodes would be better but I can not find these to fit either the prop. or leg. The hanging anode is connected to the top of the leg and like the proprietary ones is zinc but every few weeks I rub it shiny with rough abrasive paper, I have not enough confidence to use different metals.
However many of the boats run by the local charter company which winter in the same yard have saildrives and on some anodes are not an obvious priority and I can find no undue deterioration. Some locals think that the peaty fresh water in the canal which surely must be acidic does not cause degradation like sea water, I am not convinced and as a first step I have almost stopped using shore power at my berth. Thanks again, and if there is any more info. not covered I would appreciate its addition.
I suspect that part of my problem is my one design racing background where everything had to be ultra smooth and we used to burnish the antifouling. One of the Sigmas I purchased came from Burnham on Crouch and had a massive hull anode on two stout bolts, of course we had to take this off and fair everything if we were to be competitive!!! To compensate I hung it over the side of the cockpit with a heavy copper cable bonded to the circuit which connected all the skin fittings and while it eroded steadily over the years the shaft anodes degraded slowly and the prop etc. stayed in good condition for the seven years I kept the boat. However in those days the boat was in sea water most of the time. My current boat has a Volvo saildrive This is the first time I have ever had one of these with all the problems described above and it is only now that I have begun to think through the problem. (It is difficult to find an affordable Scandanavian performance boat that has shaft drive.) I believe aluminium anodes would be better but I can not find these to fit either the prop. or leg. The hanging anode is connected to the top of the leg and like the proprietary ones is zinc but every few weeks I rub it shiny with rough abrasive paper, I have not enough confidence to use different metals.
However many of the boats run by the local charter company which winter in the same yard have saildrives and on some anodes are not an obvious priority and I can find no undue deterioration. Some locals think that the peaty fresh water in the canal which surely must be acidic does not cause degradation like sea water, I am not convinced and as a first step I have almost stopped using shore power at my berth. Thanks again, and if there is any more info. not covered I would appreciate its addition.
