Electrolysis

[TomBettle]

Hi All

 

I am rather bored and having to work today, so have been browsing through one or two bits and bobs and tidying up my PC.

 

At SMB, we always explain about electrolysis and it's effects during handover of a new boat, however our owners have to cram so much info in they sometimes forget so a while ago I wrote a simple document to help advise our customers about electrolysis and anodes etc.

 

I have attached the details below, admittedly it is much more pertinent to those of you who keep your boats in the water, particularly in a marina, but useful none the less.

Apologise for the references to Southern Motorboats etc as it was originally for our owners and not the general public. Also it was written by me and I am very non scientific and not a writer at all so please take it as written for laymen by a layman.

 

Hope it is useful

Tom

 

********************************************************************

 

 

Electrolysis on the South Coast

Advice from the team at Southern Motorboats

 

All metal, including stainless steel, can and will suffer from corrosion if care is not taken to prevent it.

Your new boat is fitted with "Anodes" which are made of a soft metal (usually zinc) and electrolytic current will corrode these instead of your expensive propellers and other metal objects on the boat.

Anodes are the boat owner

[spNOam]

Hi Tom,

I have an alloy fuel tank, what would you do to prevent elecrolysis in this area....it has a fuel gauge which is connected to the battery....any advice gratefully received.

 

Geoff

[TomBettle]

Hi Geoff

 

You should find that so long as your anodes are in place and connected then you should have little problem.

 

One or two members of the forum are far more scientific about these things than me and may well be able to gve some proper technical info.

 

If you keep your boat in the water then she will probably have an anode on the transom, one on the shaft or around the outdrive and if it is an outboard there will be one on the outboard, howevr this wold normally get hardly any wear as it can be left trimmed up.

 

Duncan, Charlie, Pete and anyone with a better knowledge than me:

Do you guys have anything to input to help Geoff?

 

Tom

[Afishionado]

A remark made to me whist I was fitting a new shiny anode to my Romany when I had it at Cobbs.....

 

Onlooker "You want to give that a good coat of paint mate"

 

Me "Really?"

 

Onlooker " Yes mate, if you don't it'll just sorta melt away, it's the sea water mate, the salt rots it"

 

Pregnant silence

 

Me "Oh, right oh, thanks for the tip"

 

Onlooker walks off

 

John (inside boat in the bilge tightening up on throughbolt) "Kin idiot!"

 

You can not make this sort of stuff up!

 

By the way has any one else got any real anecdotes. I am sure Tom and Charlie must have.

 

Mad Mike

 

[spNOam]

Thanks for your replies, I have two anodes on the outboard, one at the bottom of the transom bracket which is permanently immersed & one on the leg, I take it that I should/need not have anything attached to the alloy fuel tank?

[TomBettle]

You should find the whole lot is "earthed" (not sure if that is the correct term) through to the anode on the transom bracket through the boats wiring.

 

I woud guess it will be fine.

[TomBettle]

By the way has any one else got any real anecdotes. I am sure Tom and Charlie must have.

 

Mad Mike

Mike

 

I have to say that I still have big L plates on my back on all things boating and so I am often the one putting my foot in it or buggering it up.

 

You tend to learn by your mistakes and I certainly do!

 

My two best have been:

 

1) Fuel guage reads 1/4 on a new on tested boat (new boats don't arrive with more than enough fuel to get the engine off the crane slings) so I take some buyers out on a sea trial. Promptly run out of diesel and drift alongside one of the thousands of boats on the river Hamble. The boat just happens to have an instructor onboard who's offices are next dor to one of our biggest competitors - I become the laughing stock of the next boat shows Jeanneau dealers!

 

2) My own shiny new boat arrives and I lovingly commission her and do all the fitting and mods myself - except for the VHF which is on back order with Raymarine.

Can't wait any longer to use the boat so chuck my handheld in the holdall a couple of skipper mates tell me which wrecks to fish as they will keep an eye on me and I head 25 miles due South.

24 miles due South everything goes solid as we pick up a floating cargo net round the prop. Bugger!!! Go to grab the handheld only to realise I left the holdall in the car. At that moment our kipper mates come past on their way to Alderney, see we have a problem and help by calling the coastguard.

A very annoyed Whiskey Bravo winchman drops a VHF to us and dissapears and we proceed to talk in and then be towed in by Weymouth lifeboat.

Embarrassing enough until you realise that Meridian are filming on the chopper and the BBC were filming Seaside Rescue on the lifeboat!

Needless to say the MCA got their VHF back, the RNLI got a generous donation and the BBC got denied the use of the footage (too late for Meridian as it was already on the 6 0'clock news) !!!

 

You live and learn!

 

Tom

[Afishionado]

Let he who without sin cast the first stone Tom

 

Any chance of seing the Beebs video?

 

My best was trying to lift the dog over the gunnels. The dog stayed in the water and I joined the dog. Meanwhile the Romany gently chugged on with my then wife and two kids in it trying not to laugh. The dog thought it was hilarious too.

 

Mad Mike

[Newboy]

I might be wrong but let see.

 

Why would the tank need anode? I thought it is only for metal which gets into contact with sea water?! Surely the tank is inside the hull and not in direct contact with sea water.

 

Not sure if the tank is earthed by the battery, the gauge is probably sitting on a nonconductive sill, and most the of gauge is probably plastic anyway.

[TomBettle]

I might be wrong but let see.

 

Why would the tank need anode? I thought it is only for metal which gets into contact with sea water?! Surely the tank is inside the hull and not in direct contact with sea water.

 

Not sure if the tank is earthed by the battery, the gauge is probably sitting on a nonconductive sill, and most the of gauge is probably plastic anyway.

Hi Kam

 

That s why I need one of the guys with more expert knowledge of why it happens rather then me, but no it doesn't have to be in contact with the water itself.

 

My very limited understanding (I have seen the effects) of electrolysis is that it isn't actually "rust" in the normal sense of the word, but an electrolytic current (posh word, not sure exactly what it means) that runs through the water and when it makes contact with a metal surface will begin to corrode it. If that metal surface is itself in contact with something else metal then the effect will in time pass on t that and then on to the next bit and so on. Again sorry for the limited understanding, but most boats have wiring througout them. For example an outboard is wired to throttle controls and ignition switches and so on and so the effect can pass through the whole boat in time.

Soft zinc anodes help prevent the effects of electrolysis as the corrosion effects the softest metal surface on the boat first (the zinc anode). The anodes must be connected into the whole boats system for this to work, if they are simply bolted to the boat without being connected in they will corrode slowly (more slowly), but the electrolysis will be effecting the rest of the boat at the same time.

 

You can slow down the effects by not plugging in to shore power needlessly and by turning off your batteries when you leave the boat, however the effects are speeded up by poor marina wiring, boats on shorepower all around you and metal in the water such as marina piles etc.

 

Is that any clearer?

 

Like I said, I am a layman and that is my basic understanding. I am hoping one of the more expert members of the club, may be able to contribute

 

Tom

[spNOam]

Tank is earthed to the battery, battery is connected to the engine, engine is connected to the anodes, anodes should therefore do the eroding not the fuel tank, (I think) Fuel gauge is made of metal (stainless steel cover, brass connector, anodised steel float rod, I presume the enclosed unit contains copper windings & carbon brush rheostat type assembly)

I just want the best for my tank to ensure its longevity.

 

Geoff

[Newboy]

I might be wrong but let see.

 

Why would the tank need anode? I thought it is only for metal which gets into contact with sea water?! Surely the tank is inside the hull and not in direct contact with sea water.

 

Not sure if the tank is earthed by the battery, the gauge is probably sitting on a nonconductive sill, and most the of gauge is probably plastic anyway.

Hi Kam

 

That s why I need one of the guys with more expert knowledge of why it happens rather then me, but no it doesn't have to be in contact with the water itself.

 

My very limited understanding (I have seen the effects) of electrolysis is that it isn't actually "rust" in the normal sense of the word, but an electrolytic current (posh word, not sure exactly what it means) that runs through the water and when it makes contact with a metal surface will begin to corrode it. If that metal surface is itself in contact with something else metal then the effect will in time pass on t that and then on to the next bit and so on. Again sorry for the limited understanding, but most boats have wiring througout them. For example an outboard is wired to throttle controls and ignition switches and so on and so the effect can pass through the whole boat in time.

Soft zinc anodes help prevent the effects of electrolysis as the corrosion effects the softest metal surface on the boat first (the zinc anode). The anodes must be connected into the whole boats system for this to work, if they are simply bolted to the boat without being connected in they will corrode slowly (more slowly), but the electrolysis will be effecting the rest of the boat at the same time.

 

You can slow down the effects by not plugging in to shore power needlessly and by turning off your batteries when you leave the boat, however the effects are speeded up by poor marina wiring, boats on shorepower all around you and metal in the water such as marina piles etc.

 

Is that any clearer?

 

Like I said, I am a layman and that is my basic understanding. I am hoping one of the more expert members of the club, may be able to contribute

 

Tom

Are you saying VHF, fishfinder and plotter will just melt into a pile of rust?

[TomBettle]

Tank is earthed to the battery, battery is connected to the engine, engine is connected to the anodes, anodes should therefore do the eroding not the fuel tank, (I think) Fuel gauge is made of metal (stainless steel cover, brass connector, anodised steel float rod, I presume the enclosed unit contains copper windings & carbon brush rheostat type assembly)

I just want the best for my tank to ensure its longevity.

 

Geoff

Geoff from what you have written and my basic understanding that is correct and your tank should be safe and sound(!), but change your anodes once they are worn.

 

Tom

[TomBettle]

Are you saying VHF, fishfinder and plotter will just melt into a pile of rust?

Hi Kam

 

I really wish one of the guys witha more scientific understanding would join in here as I starting to get out of my depth and run the risk of providing missinformation.

The document I put on is a very simple advice sheet saying keep an eye on your anodes as a

[Afishionado]

Anodes guard against electrolysis which is an electrical action as the name sugests.

Rust on the other hand is a chemical reaction caused by the chemical elements in a metal reacting with oxygen in water and turning into an oxide (rust = hydrated iron oxide)

 

Metals are divided into catogories of 'Nobility' the weakest on the scale being the one that will be affected by electrolosis the first when it is placed in a circuit with another more noble metal. The process is electrochemical: the metal enters solution in the form of ions, atoms that have lost one or more electrons. The electrons flow through the metal and are discharged into the surrounding water.

So to make it simpler for me to explain. The leakage of electrical current, static or generated from a boat equipment that in any way has an electrical path to the water (engine prop shaft fuel tank if connected through copper or metal piping etc), will try to earth its self into the surrounding water. Electricity is a flow of electrons along a conductor as the flow of electrons travels through any metal condutor it takes with it stray atoms starting with the atoms of the least noble metal. Taking this as inevitable if one supplies a piece of metal that is very very low on the scale of nobility, it will be this metal that loses (sacrifices) it's atoms first, thus saving loss of atoms from more noble metals.

In application this means that every metalic item that is in the boat should be earthed to a common earth which in turn is connecter to the sacrificial anode and a return wire from the anode back to battery positive thus completeing the circuit. By doing this tha only loss of atoms will be from the very low nobility of the zinc content of the anode.

 

Items that are not in electrical contact with the water will not be affected by electrolosis as they do not have a way of earthing out to the water.

 

Mad Mike

[Bob F]

I assume that a metal fuel tank must be earthed to prevent static build up, which could otherwise be potentially explosive if enough static charge was present to ignite the gas fumes.

 

The earth will be connected to your batteries, which is inturn connected to your outboard and thence to the sacrificial anodes on the outboard. So, I'd say your fuel tank is protected providing you replace the anodes and ensure that the earth connections are in good order.

 

Unlikey that plotters and FF's will turn to rust, but it could cause corrosion on the power terminals inside the units.

 

The 12V Handbook is a good reference for Electrolysis.

 

BF

[TomBettle]

Anodes guard against electrolysis which is an electrical action as the name sugests.

Rust on the other hand is a chemical reaction caused by the chemical elements in a metal reacting with oxygen in water and turning into an oxide (rust = hydrated iron oxide)

 

Metals are divided into catogories of 'Nobility' the weakest on the scale being the one that will be affected by electrolosis the first when it is placed in a circuit with another more noble metal. The process is electrochemical: the metal enters solution in the form of ions, atoms that have lost one or more electrons. The electrons flow through the metal and are discharged into the surrounding water.

So to make it simpler for me to explain. The leakage of electrical current, static or generated from a boat equipment that in any way has an electrical path to the water (engine prop shaft fuel tank if connected through copper or metal piping etc), will try to earth its self into the surrounding water. Electricity is a flow of electrons along a conductor as the flow of electrons travels through any metal condutor it takes with it stray atoms starting with the atoms of the least noble metal. Taking this as inevitable if one supplies a piece of metal that is very very low on the scale of nobility, it will be this metal that loses (sacrifices) it's atoms first, thus saving loss of atoms from more noble metals.

In application this means that every metalic item that is in the boat should be earthed to a common earth which in turn is connecter to the sacrificial anode and a return wire from the anode back to battery positive thus completeing the circuit. By doing this tha only loss of atoms will be from the very low nobility of the zinc content of the anode.

 

Items that are not in electrical contact with the water will not be affected by electrolosis as they do not have a way of earthing out to the water.

 

Mad Mike

Thanks Mike!!!!

 

I was starting to worry that I had my mucking fords wuddled for a minute, but your explanation is (I think) the technical explanation of what I was trying to say.

 

Cheers!

Tom

[shytalk]

metal petrol tanks should have an earth wire as should a metal filler cap on a built in tank to avoid static sparks from the nozzle of a petrol pump !! boooom !!!!

[Afishionado]

metal petrol tanks should have an earth wire as should a metal filler cap on a built in tank to avoid static sparks from the nozzle of a petrol pump !! boooom !!!!

Only those tanks fixed to or inside the boat. The current flow is from the appliance filling the tank realeasing it's static charge back into the boats electrical field. To make the refueling correctly safe (only required with petrol or imflamable liquid gases) then PRIOR to filliing, an earth strap must be clipped from the tank in the boat back to the fueling device. You can have your tank earthed to anything you want and it will do no good unless you connect electricaly the tank and the filler nozzle .

 

O/B tanks do not need earthing as they should be removed from the boat for refueling and do not have any direct electrical contact with the boats earth system.

 

Mad Mike (Writing this at ohm)

[Paul D]

Mike,

 

Interesting thought regarding O/B tanks as I must admit I usually fill mine up whilst it is sitting in the boat . I suspect that any static charge would have been dispersed through the trailer and trailer wheels though ( says he with fingers crossed ! ).

 

Not totally convinced that a boat being filled from a pump is not electrically connected to the pump in any case. This connection would be via tank to anode to sea water to earth to pump. Does this sound feasible ?

 

 

[Afishionado]

Not totally convinced that a boat being filled from a pump is not electrically connected to the pump in any case. This connection would be via tank to anode to sea water to earth to pump. Does this sound feasible ?

 

There is no need for you to be convinced at this stage Paul. You will become convinced when you are surrounded by an interesting yellow and red affect which is accompanied by a slight warming of the body

 

Jokes apart like any moving machinery in certain conditions a static electrical charge builds up in the framework of the petrol pump. This will seek the easiest earth route it can, and if need be even jump a gap if the charge has been built up high enough. To safely fill an inboard fixed tank one must fix an earthing line from the petrol pump to the earth system of the boat. If the fixed tank has been properly installed and earthed to a common earth and /or the anode earth any static discharge will favour this rout rather than jump the higher impedence of a gap twixt tank and filler. And yes you are dead right about the course of the flow as it is circular you can jump in at any point. Static charge in pump body, earth lead to tank, tank earth lead to anode, anode through salt water to earth.

 

Mad Mike

 

PS a paranoid perfectionist would probably say lift a metal O/B tank out of the boat and onto the ground for filling. But with todays plastic tanks who bothers.

[Newboy]

I suspect that any static charge would have been dispersed through the trailer and trailer wheels though

Just think how sometimes you goup to a car and get 'zap' by the stattic .

 

 

[great white]

Electrolosis can be a big problem

 

especially for boats kept in Marinas with all the additional metals used to hold the pontoons in place and the electricity to the boats.

 

Sail drive and outdrive anodes can dissapear very quickly if they are not backed up by larger anodes fitted onboard.

 

Sacrificial Zinc anodes work best in Line of sight or close to the worse area of likely electrolosis. [stainless shaft, Bronze prop, rudder area] all anodes should be connected in circuit to share the work load.

 

The electrolosis really gets going if you have a problem on the boats earth circuit and are plugged in to the Marina power.

 

A newish Yacht here came out for maintenance to find his Prop was beyond repair and his stainless shaft looked like swiss cheese with small holes all over it. after replacing shaft, prop and P bracket, further checks proved that the boats electric system was at fault and had in effect accelerated the electolosis.

 

I reccomend to the berth holders they suspend a large anode over the stern between twin outdrives or fit a large anode on the transom to increase protection.

They are told to connect these in to the anode circuit by a cable, [ There is one over the back of GW as I Type this] but several just seem to hang them over on a bit of cord??? [ Chocolate teapot time]

 

Charlie

[overdraft]

The fuel tank should be bonded down to the anodes this is to reduce the chance of a static shock which in the worse case could ignite the fuel,

there should be bonding cable linking all the metal skin fittings togeather this is to give the quickest route back to the anodes. the battery neg should also be included in this circuit.

 

If the boat is conected to shore power all the time it would be worth getting hold of a galvonic isolater this goes between the ac earth and the dc/ battery neg to block any stray currents.

 

if all the skin fittings are of the same material eg all stainless then electrolosis will not take place it only happens when 2 discimular types of metal are joined togeather.

[spNOam]

All fittings are of the same material, I am tempted to find a small anode to attach between the fuel tank & the battery earth cable just to see if any erosion is taking place. Is this a good idea?