winsbury
New member
since we don't use shore power I was surprised when lifting our outboard from the well which has been in the water for 4 months after fitting a new anode to find its virtually gone. Is this normal ?
vanishing anode
- Thread starter winsbury
- Start date
VicS
Well-known member
Not very large as rule. If you must leave the outboard with its lower end submerged 24/7 perhaps bolting larger anodes on to the AV plate is something you could consider.
If there is any sign of corrosion of the outboard leg it would be a good idea to check the DC electrical system for any possible obscure faults that might lead to electrolysis esp. if you have any other underwater bits and pieces that may be connected to the system or dont totally isolate the batteries when the boat is not in use.
Electrolysis however would be likely to dissolve the whole outboard in a few months!
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winsbury
New member
well that's encouraging 
Its a pretty small anode to start with, that is very true. I have ordered a replacement and will see if there's anywhere to fit a larger one. There's no sign of any damage elsewhere (yet!) I did notice while motoring the other day and holding the pushpit with damp hands that I was getting a tingling sensation so seems there is some connection from the electrical system to the handrail but I cant think of any good reason for this so unless there's some wisdom to have that connected which I'm missing I'll disconnect it when I go down next.
I'm currently treating the bottom of the leg with Hempel Underwater Primer and Aluxtra AF as I was also surprised how much growth there was already. Hopefully that should reduce potential damage to the leg as there's no practical way of lifting the engine when not in use.
Its a pretty small anode to start with, that is very true. I have ordered a replacement and will see if there's anywhere to fit a larger one. There's no sign of any damage elsewhere (yet!) I did notice while motoring the other day and holding the pushpit with damp hands that I was getting a tingling sensation so seems there is some connection from the electrical system to the handrail but I cant think of any good reason for this so unless there's some wisdom to have that connected which I'm missing I'll disconnect it when I go down next.
I'm currently treating the bottom of the leg with Hempel Underwater Primer and Aluxtra AF as I was also surprised how much growth there was already. Hopefully that should reduce potential damage to the leg as there's no practical way of lifting the engine when not in use.
vyv_cox
Well-known member
Could you fit an anode on a cable to hang alongside the fitted one when the boat is not in use? Needs to be connected to the leg but presumably there is electrical contact throughout the outboard.
gabriel
New member
i am haveing problems with electrolysis how can check where power leak starts
vyv_cox
Well-known member
Lots more information needed. What are the symptoms, what components are we talking about, what is connected to what?
VicS
Well-known member
Do you really mean electrolysis or galvanic corrosion?
The former is driven by a external power source, eg your 12volt system. It could cause vey rapid corrosion. The latter is due to "dissimilar" metals in contact or connected to each other.
Can you provide some details of your problems.
It would have been sensible to have started a new thread of your own rather than hijacking an existing one
gabriel
New member
my boat is a pegasus 26 ft bilge keel problem started last year the bilges where badley eating away at end of season i sanded all down re painted and fitted anodes to both keels this year both anodes were badley corroded as were the bilges there is big flakes of corroded metal roughley 1/8 off a inch deep x 2 inch diameter. the anode on the sail drive is not touched first time on forum did not no to start thread
VicS
Well-known member
First few questions
Is the boat kept in a marina ?
If yes
Do you have a shorepower installation and if so do you normally leave it plugged in, even if not actually in use?
Where is the boat moored ?
I dont know what Vyv will make of this but I am thinking in terms of electroysis at a result of a leakage from the positive side of the DC system to the bilge keels with the saildrive acting as the return pathe to negative
Any electrical connections that you know of to the keels ?
Do you fully isolate the DC system when leaving the boat or is any part of it left switched on .
It must be significant that there is no damage to the sail drive or its anode. What engine and drive is fitted?
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vyv_cox
Well-known member
Answers to VicS' questions will help a lot. Additionally, are you in 'pure' seawater or is the berth in fresh/brackish water?
VicS
Well-known member
Just add another thought while waiting for more info, and before I forget it. Maybe possible for a DC fault on an adjacent boat in a marina to be the cause if both connected to shorepower ???????
syfuga
Member
Yup, people are hinting at it, but reserving judgement!
There is a very real risk in a marina environment using a shore power connection over a long period. If the earth connection on the marina is inadequate, then it can set up a path from your earth on the boat to the sea. A galvanic isolator in the shorepower earth will help to protect against these relatively low voltage-driven currents, and reduce galvanic corrosion on board.
A motor boat moored alongside us once in Lagos, Portugal, almost sank when his large anodes corroded away to the point where the bolts securing them fell out, and it began to take on water. It took me several days to persuade the marina to take note of the repetitive automatic bilge cycles.
There is a very real risk in a marina environment using a shore power connection over a long period. If the earth connection on the marina is inadequate, then it can set up a path from your earth on the boat to the sea. A galvanic isolator in the shorepower earth will help to protect against these relatively low voltage-driven currents, and reduce galvanic corrosion on board.
A motor boat moored alongside us once in Lagos, Portugal, almost sank when his large anodes corroded away to the point where the bolts securing them fell out, and it began to take on water. It took me several days to persuade the marina to take note of the repetitive automatic bilge cycles.
gabriel
New member
i have my own mooring in sea water in donegal there is no connections to bilges the bilge bolts seem rusty on starboard side i am going to take bilge off this winter to repair i fitted a new engine 4years ago its a beta 15 hp the anode on the engine was wasted away i replaced it the start off year when i last checked it 6 weeks ago it was ok i have been turning of the battery power half way through season its hard to tell i think the problem has not been as bad there is no shore power i did sand bilges down to years ago and painted them with red lead then antifoul them i not sure if that makes a differance thanks mean time
Tranona
Well-known member
Think your problem is nothing to do with galvanic action or electrolysis, but straightforward rust, which will not be cured by putting anodes on the keels. Similarly the erosion of the anode in your engine is nothing to do with other parts of the boat, but occurs because of the dissimilar metals used in the heat exchanger.
Rust on the keel bolts inside suggest a seawater leak somewhere and water getting in as the bolts are mild steel. You will probably find if you clean the heads of the keel bolts that there is also probably a mild steel plate underneath. Remove the nuts and replace the plates, and possibly the nuts and then paint them to reduce the chance of rust in the future. The keel castings themselves are difficult to deal with as you need to get them really clean and then prime immediately. Various ways of doing this depending on what facilities you have and how much hard work you are prepared to do.
vyv_cox
Well-known member
Information on page 342 of this book http://books.google.co.uk/books?id=...#v=onepage&q=red lead paint sea water&f=false says that red lead paint is unsuitable for protecting steel (= iron) ships' hulls underwater. I think you might be better off using a conventional metal primer for keels, e.g. Primocon, or better still an epoxy. You refer to sanding but this is possibly not aggressive enough for the job. Grit blasting is undoubtedly the best, but can be inconvenient and expensive. Needle gunning comes next, followed by angle grinding. Paint should be applied within half an hour in warm, dry conditions.
winsbury
New member
Pegasus keel bolts should be sealed in epoxy so impossible to examine...if someone has replaced them its important mild steel and not stainless are used as the dissimilar metals will corrode and the stainless will also suffer crevice corrosion when re-epoxied.
gabriel
New member
I am going to take bilges off sand blast and do fibreglass repair to worst areas then epoxy I just do not want to do all this work then find problem still there next year it is there any way or any thing I can do to make sure I do not have same problem and could u give me information on what paints fillers and epoxy to use thanks
vyv_cox
Well-known member
The vast majority of yachts have stainless steel keel bolts with cast iron keels, without suffering crevice or galvanic corrosion. Provided the keel is correctly bedded on an appropriate sealant that keeps the water out there will be no corrosion.
gabriel
New member
I have taken one off the keels of I am going to get it sand blasted what under coat fillers and epoxy should I use to repair ? Can I put epoxy on to bear metal thanks
coreng
New member
Best naval practice to surely appreciate anode's efficiency/consumption and identify harmful stray currents (these go out an attacked immersed metal right into the water) remains equipment 's electro-chemical potential measurement through dedicated electrode. Corrosion might occurs if value are over -800 mV (the upper the value, the stronger the corrosion) and no shift should be noticed with DC, or shore-power plugged on. If values remains OK, then anode's depletion is due to environmental factors. This is true for every immersed metal part, even with recreational boats.
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