Could a Stainless P:ropeller cause galvanic corrosion of an Alloy power head.

[Bobpen]

I am asking for a friend.😉
A more simple question as some people get confused easily
Hypothetically.
A stainless-steel propeller is attached to an aluminium alloy power head by a drive shaft.
The hot seawater from the alloy power head exits the motor through the stainless propeller hub.
Galvanic corrosion occurs when dissimilar metals are connected by an electrolyte.
An example of a marine alloy from Mercury Marine Engines contains tin, copper, zinc, copper, and aluminium
316 Stainless contains iron, chromium, nickel and molybdenum.
What could go wrong?

[shortthenlong]

124086

.....

[Dignity]

I am asking for a friend.😉
A more simple question as some people get confused easily
Hypothetically.
A stainless-steel propeller is attached to an aluminium alloy power head by a drive shaft.
The hot seawater from the alloy power head exits the motor through the stainless propeller hub.
Galvanic corrosion occurs when dissimilar metals are connected by an electrolyte.
An example of a marine alloy from Mercury Marine Engines contains tin, copper, zinc, copper, and aluminium
316 Stainless contains iron, chromium, nickel and molybdenum.
What could go wrong?

Ok for my edification as I am simple and easily confused, if the prop hub is SS and it is sitting on a SS shaft how does that exacerbate the so called galvanic reaction that is occurring. Now I do remove my prop regularly and surprisingly there is still always a coating if grease in the splines, maybe that's causing the problem.

[scottar]

Only if you unbolt them both and put them in a jar of electrolyte on your bedside table. 🤦

PS - make sure to unbolt the anodes first or you won't get the desired result

[Bobpen]

Only if you unbolt them both and put them in a jar of electrolyte on your bedside table. 臘

PS - make sure to unbolt the anodes first or you won't get the desired result
It is hard to use the boat with the propeller off.
Have you ever used a boat?

[Bobpen]

Only if you unbolt them both and put them in a jar of electrolyte on your bedside table. 臘

PS - make sure to unbolt the anodes first or you won't get the desired result
The sea water is an electrolyte. Look it up.
When I use the motor it is sea water.
Is there anyone else out there?

[Bobpen]

Ok for my edification as I am simple and easily confused, if the prop hub is SS and it is sitting on a SS shaft how does that exacerbate the so called galvanic reaction that is occurring. Now I do remove my prop regularly and surprisingly there is still always a coating if grease in the splines, maybe that's causing the problem.
The stainless propeller is connected electrically to the power head through the drive shaft it has a giant nut holding it on.
The power head is alloy.
The alloy power head then connects to the stainless propeller though the hot seawater electrolyte which leaves though the stainless propeller hub with the exhaust gases.
The dissimilar metals cause galvanic corrosion.
Simples.,

[billfisher]

The seawater comes into the motor before the propeller so the two aren't connected by electrolyte. In any case the motor isn't running for more than 50 - 100 hours a year for most recreational use which is not a lot of time for corrosion to occur.

[Bobpen]

The seawater comes into the motor before the propeller so the two aren't connected by electrolyte. In any case the motor isn't running for more than 50 - 100 hours a year for most recreational use which is not a lot of time for corrosion to occur.
The hot sea water from the alloy power head exhausts through the stainless propeller.
A direct connection.
I worked out my boat was in seawater for about 1,600 hours before there was enough corrosion to destroy the engine mounts.
Most of those hours the boat was at anchor but the motor was still full of sea water probably still warm.
Anyone else out there?

[Steeler]

Great thread:sleeping:

[Dignity]

The stainless propeller is connected electrically to the power head

This has me totally flummoxed, how?

[gazza2006au]

Is you're "friend" a "nut" that holds the propeller on? I had to clarrify before disorderly calls me a useless tool :D

[scottar]

It is hard to use the boat with the propeller off.
Have you ever used a boat?

So get a bigger jar and put the whole motor in if you don't want to take the prop off. Do I have to think of everything Bob??????

I only use my boat occasionally .......... you got me there. The rest of the time I have to work..........maintaining a fleet of commercial vessels..............made up of dissimilar metals including aluminium, steel bronze, stainless, copper nickel, cast iron and probably a few others.............that get stored in a giant puddle of electrolyte..............by changing the anodes which protect them against galvanic corrosion among other things...............who would have thought huh.


You are right though Bob........some people do get confused easily.

[Dignity]

Is you're "friend" a "nut" that holds the propeller on? I had to clarrify before disorderly calls me a useless tool :D

Ha ha, Gazza, I think in this case Disorderly would be laughing alongside with you. I suspect this is a Troll post, especially when he queries whether Scottar who works and spends his off time on the water whether he has been on a boat is laughable.
I actually sent the copy of all these posts to a scientist mate who specialises in metallurgy and has spent 2 seasons in the Antarctic so no fool and he just laughed and did say some rather harsh things and said I was being had, so I'll stop commenting now.

Edit: I see Scottar got in before me.

[Noelm]

The hot sea water from the alloy power head exhausts through the stainless propeller.
A direct connection.
I worked out my boat was in seawater for about 1,600 hours before there was enough corrosion to destroy the engine mounts.
Most of those hours the boat was at anchor but the motor was still full of sea water probably still warm.
Anyone else out there?
interesting you never mentioned your boat was moored in your other thread!

[shaungonemad]

interesting you never mentioned your boat was moored in your other thread!

Pretty sure he is talking about the accumulative time that the boat was in the water during various trips.


Sent from my iPhone using Tapatalk

[Noelm]

Scientifically there is a huge difference to dissimilar metal sitting in an electrolyte to dissimilar metals connected together electrically sitting in the same electrolyte.

[Lovey80]

I am wondering if in 13 years when the new engine corrodes out if he’s going to have all the other stainless parts removed from his next engine. Could be difficult getting a prop shaft galvanised then lapped perfectly so a prop will fit nicely.

[Bobpen]

Great thread:sleeping:
I cost me $16,000.
I hope Karma hits your engine. AH

[Bobpen]

I am wondering if in 13 years when the new engine corrodes out if he’s going to have all the other stainless parts removed from his next engine. Could be difficult getting a prop shaft galvanised then lapped perfectly so a prop will fit nicely.
If I had never had a Stainless prop it would have saved me $16,000.
Hope Karma hits your motor AH
I don't have a stainless prop now and never will.
I am capable of LEARNING.

[Bobpen]

Scientifically there is a huge difference to dissimilar metal sitting in an electrolyte to dissimilar metals connected together electrically sitting in the same electrolyte.
The Prop and the power head are connected by the drive shaft and the power head and the prop are connected by hot sea water.
Try it in a glass of sea water. How do you think zinc anodes work? They sit in sea water. The anode dissolves. It is fact.
It isn't rocket science.
Any time you put a stainless prop in seawater you are gradually destroying your alloy power head.
It might take 13 years.
Try it.

[Bobpen]

This has me totally flummoxed, how?
The propeller is bolted to the drive shaft which is attached to the power head.
Like a large wire.

[Bobpen]

Pretty sure he is talking about the accumulative time that the boat was in the water during various trips.


Sent from my iPhone using Tapatalk
To Noelm: Boat was anchored while fishing.
I should use smaller words. Sorry.

[DATCOL]

I think my motor is pretty safe as the hot water coms out of the motor past the stainless prop & disappears into the ocean dose not suck back in past the prop

[Steeler]

I cost me $16,000.
I hope Karma hits your engine. AH


You have a good day too champion.

[stevej]

I cost me $16,000.


you got that right you cost yourself 16,000 because you have no idea what your doing with your home servicing and maintenance

and really calling everyone a holes now
your more likely to convince people the earths flat then the rubbish theory you have to why your engine died

[billfisher]

The hot sea water from the alloy power head exhausts through the stainless propeller.
A direct connection.
I worked out my boat was in seawater for about 1,600 hours before there was enough corrosion to destroy the engine mounts.
Most of those hours the boat was at anchor but the motor was still full of sea water probably still warm.
Anyone else out there?

The seawater exits through the prop as you said - then it goes out into the ocean. So there is no electrolyte connecting the powerhead to the prop, That means a galvanic cell is not formed. Also it has already been pointed out that the cooling water drains out of the powerhead as soon as the motor is switched off.

[Bobpen]

Ha ha, Gazza, I think in this case Disorderly would be laughing alongside with you. I suspect this is a Troll post, especially when he queries whether Scottar who works and spends his off time on the water whether he has been on a boat is laughable.
I actually sent the copy of all these posts to a scientist mate who specialises in metallurgy and has spent 2 seasons in the Antarctic so no fool and he just laughed and did say some rather harsh things and said I was being had, so I'll stop commenting now.

Edit: I see Scottar got in before me.
On another offshore marine project (not a mariculture pond) we had some 6 inch plumbing fittings made from Gun Metal.
The Nuts, Bolts and Couplings were all made from the same metal pour to prevent galvanic corrosion from slightly dissimilar mixes of the gun metal.
There are a lot of know nothings on this forum.
Boring but you try to help them .
Some people can't even understand galvanic corrosion is caused by connecting dissimilar metals with an electrolyte.
How many times can you say it?
Let's try again. I am used to dealing with toddlers. Constant repetition.
Some people can't even understand galvanic corrosion is caused by connecting dissimilar metals with an electrolyte.

[Bobpen]

The seawater exits through the prop as you said - then it goes out into the ocean. So there is no electrolyte connecting the powerhead to the prop, That means a galvanic cell is not formed. Also it has already been pointed out that the cooling water drains out of the powerhead as soon as the motor is switched off.
Do you seriously think there is not enough film of seawater left in the powerhead to conduct electricity?
So why flush motors at all then. How stupid are you? When I drain my kitchen sink the water leaves a film I don't use Rainex on it.
On another offshore marine project we had some 6 inch plumbing fittings made from Gun Metal.
The Nuts, Bolts and Couplings were all made from the same metal pour to prevent galvanic corrosion from slightly dissimilar mixes of the gun metal.
There are a lot of know nothings on this forum.
Boring but you try to help them .

[billfisher]

Do you seriously think there is not enough film of seawater left in the powerhead to conduct electricity?
So why flush motors at all then. How stupid are you?
On another offshore marine project we had some 6 inch plumbing fittings made from Gun Metal.
The Nuts, Bolts and Couplings were all made from the same metal pour to prevent galvanic corrosion from slightly dissimilar mixes of the gun metal.
There are a lot of know nothings on this forum.
Boring but you try to help them .

I'm not stupid at all - in fact I'm a qualified chemist. Check what happens when you drain the bath or sink next time. Water has a low viscosity and has the property of surface tension. It we bead into droplets rather than form a continuous film.

[Steeler]

Less engagement with the OP the better me thinks.

[shortthenlong]

Do you seriously think there is not enough film of seawater left in the powerhead to conduct electricity?
So why flush motors at all then. How stupid are you?
On another offshore marine project we had some 6 inch plumbing fittings made from Gun Metal.
The Nuts, Bolts and Couplings were all made from the same metal pour to prevent galvanic corrosion from slightly dissimilar mixes of the gun metal.
There are a lot of know nothings on this forum.
Boring but you try to help them .

124107

Turns out we have an alchemist among us

[Dignity]

Do you seriously think there is not enough film of seawater left in the powerhead to conduct electricity?
So why flush motors at all then. How stupid are you?
On another offshore marine project we had some 6 inch plumbing fittings made from Gun Metal.
The Nuts, Bolts and Couplings were all made from the same metal pour to prevent galvanic corrosion from slightly dissimilar mixes of the gun metal.
There are a lot of know nothings on this forum.
Boring but you try to help them .

Now this is the 2nd time you have mentioned "offshore projects" , please let us know what these are, they might add some credibility to your statements so far they have NO credence according ti current scientific knowledge.
What you have probably not realised (about as polite as I can say it), is that many members on here come from some very diverse backgrounds. Whether it be as simple as massive hrs on the water, to people with an enormous scientific and engineering background.
Many have been on this forum for quite a long time and kept their background quiet.
Bobpen, you are spouting in my very humble opinion a lot of garbage and are just stirring the pot. I did say previously that I wouldn't post any more but you did get my goat up. This is my last offer on this subject, pxxs off and let things lie, agree to disagree with everyone , you are $16k worse (probably better) off with a new motor. Go fishing or whatever you do and let the rest of us think about things that really matter.

[Lovey80]

If I had never had a Stainless prop it would have saved me $16,000.

incorrect.

Hope Karma hits your motor AH
I don't have a stainless prop now and never will.
I am capable of LEARNING.

Karma already has hit my motor. It’s a 2008 model that has had a stainless prop on it since new. Flushed properly and serviced properly and is still going strong.

you still haven’t explained, even if your theory is true regarding the galvanic corrosion, how going to an ally propeller is going to help you? Everything you said was causing the anode/cathode/electrolyte scenario STILL exists!!!!

[shakey55]

This is getting way over my head. I’ve a 2000 model Johnson Oceanpro 115 hp that has a SS prop since new. Not the slightest indication of rust whatsoever, anywhere.

I just read an old THT article about a rusting etec and unfortunately he received similar comments as you have been receiving. It’s obviously NOT a common problem and I’m thinking is caused by some stray or badly connected wiring that somehow is causing the electrical field.

https://www.thehulltruth.com/boating-forum/130214-serious-problems-evinrude-e-tec-engines.html

I’m no expert in this field, but I just think somehow this may be occurring. If I’m way off course with this idea I apologise.


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[Dirtyfuzz]

Is this the elusive Kerry?

[Dignity]

Is this the elusive Kerry?

I thought it was as did others but his avatar goes back quite a few years. Maybe he is signed on under many aliases.

[fishtragic]

Sooo many rude replies to this poor lost soul. He's asked a question and nobody is constructively trying to help. Mate, just take the drive shaft out and use the outboard without it thus breaking the connection, problem solved!

[EdBerg]

I don't know if my situation has anything to do with outboards as the poster had regards to electrolytic corrosion, but many years ago when I had my 26ft boat it had a sterndrive Mercruiser S/S duoprop leg on it and I left it moored at the marina for a night or two as I was working on the trailer, anyway when I pulled it out and got it back on the trailer I noticed that the props was covered in what I assumed was ally oxide. The anode in the prop hub and ones on the cav plate were chewed up and had lost about 30% of their size. The coating was on the upper surface of the props closest to the anodes. It looked like it had been deposited there like in an electroplating process. The back of the boat had an ally duckboard, S/S legs supports, S/S live bait intake, S/S trim tabs and large ally fuel tank.

I had to scrape off the crud with a chisel and then wire brush it to remove it all. Now I suspect that it may have been stray electricity going into the water from the jetty I was tied up to, anyway I did some research and apparently Mercruiser has some sort of electrical gismo part that you connect up to the battery and to the legs to reduce the corrosion on the legs, It seems that some of their legs are subject to severe corrosion and pitting with quite a few reports of the legs being severely damaged when moored permanently. They deny everything and it may be that there was a bad batch of alloy used to cast their legs so it may be what the original poster motor may have had, was just bad alloy.

Anyway in my case I ran a 1.6mm solid S/S wire to everything metalic outside on the transom including the leg, motor and also the fuel tank and connected them all to the Neg. terminal of the battery to earth them. Spent quite a few nights on the ocean afterwards and when back on the trailer, there were no signs of new corrosion. I certainly didn't moor it back at that marina to test my theory though, but I still suspect that in my case, it was just stray current from the jetty as it happened extremely fast. You just have to wonder with the amount of reports on legs being chewed up if they used a contaminated alloy.

[scottar]

I don't know if my situation has anything to do with outboards as the poster had regards to electrolytic corrosion, but many years ago when I had my 26ft boat it had a sterndrive Mercruiser S/S duoprop leg on it and I left it moored at the marina for a night or two as I was working on the trailer, anyway when I pulled it out and got it back on the trailer I noticed that the props was covered in what I assumed was ally oxide. The anode in the prop hub and ones on the cav plate were chewed up and had lost about 30% of their size. The coating was on the upper surface of the props closest to the anodes. It looked like it had been deposited there like in an electroplating process. The back of the boat had an ally duckboard, S/S legs supports, S/S live bait intake, S/S trim tabs and large ally fuel tank.

.

This does sound like a galvanic reaction - and is similar to what we see with stainless steel strainer baskets in our cooling systems (although not that quick) where the anode material from the anode in the basket to protect the steel housing, is deposited onto the stainless. I suspect your thinking of a marina based issue is correct. The big difference with this in comparison to Bob's is that yours exhibited typical galvanic characteristics - eating away the most reactive metal in a localized reaction. A galvanic reaction doesn't bypass a more reactive metal or the same metal for some distance and set up. It's localized where the metals are in close proximity - the exact reason your prop wasn't uniformly coated in anode material. Did you have shore power connected to charge batteries?

[TheRealAndy]

If one goes back to the first question, "Could a Stainless Propeller cause galvanic corrosion of an Alloy power head.", the answer is yes. In fact, its not a question of 'could', its a confirmed 100% it will.

This is why outboards have sacrificial anodes. The sacrificial anode corrodes before the expensive bits do. Once the anode corrodes sufficiently, the other bits will start corroding.

I wonder how many here realise there is anodes bolted into the powerhead of most outboards to deal with this problem?

[scottar]

If one goes back to the first question, "Could a Stainless Propeller cause galvanic corrosion of an Alloy power head.", the answer is yes. In fact, its not a question of 'could', its a confirmed 100% it will.

This is why outboards have sacrificial anodes. The sacrificial anode corrodes before the expensive bits do. Once the anode corrodes sufficiently, the other bits will start corroding.

I wonder how many here realise there is anodes bolted into the powerhead of most outboards to deal with this problem?

There's no argument that stainless can have a galvanic reaction with aluminium Andy but it's a massive stretch between that and claiming the stainless prop is the cause of a corroded out power head on a motor that has only done 400 odd hours, is fitted with anodes and is stored on a trailer. The anodes not only allow the use of the required metals but also stop the aluminium alloy from literally eating itself away. If it was an entirely galvanic issue, I would be expecting the corrosion to be in the leg (which has been immersed for 1600 hours and is right beside the prop) more so than the power head. There are plenty of different types of aluminium corrosion Aluminium Corrosion | 13 Types Explained | Fractory (https://fractory.com/aluminium-corrosion/)

[Steeler]

Anyway who gives a toss. The OP asked a question and vehemently opposed any contrary views to his apparent question.

Those who provided alternatives got called #######s so to this entire thread may the AF minders blow the f^&*#r of a thread up and i am going to have a beer and i will get a shitload of change from $16000.00

[scottar]

Anyway who gives a toss. The OP asked a question and vehemently opposed any contrary views to his apparent question.

Those who provided alternatives got called #######s so to this entire thread may the AF minders blow the f^&*#r of a thread up and i am going to have a beer and i will get a shitload of change from $16000.00

Probably enough to buy a nice new shiny stainless steel prop......................

[EdBerg]

This does sound like a galvanic reaction - and is similar to what we see with stainless steel strainer baskets in our cooling systems (although not that quick) where the anode material from the anode in the basket to protect the steel housing, is deposited onto the stainless. I suspect your thinking of a marina based issue is correct. The big difference with this in comparison to Bob's is that yours exhibited typical galvanic characteristics - eating away the most reactive metal in a localized reaction. A galvanic reaction doesn't bypass a more reactive metal or the same metal for some distance and set up. It's localized where the metals are in close proximity - the exact reason your prop wasn't uniformly coated in anode material. Did you have shore power connected to charge batteries?

Actually Scottar, I misworded, I meant Zinc oxide rather than ally oxide, but I think you know what I meant, anyway, no, the boat was locked up everything was switched off, batteries isolated and no shore power. However there were a couple of steel trawlers close to my boat and they may have had their generators running or shore power connected. It just seemed puzzling at the time and since it didn't reoccur either due to me earthing everything, or by the fact I never moored there again so I didn't worry about it any more. But I do remember that the guys in the States had their legs severely chewed and pitted made me think that the legs may have been made from a bad batch of ally alloy, I would assume that they had anodes on their legs as well, so maybe those got chewed off quickly like mine without the owners knowing, which left the legs unprotected.

[billfisher]

If one goes back to the first question, "Could a Stainless Propeller cause galvanic corrosion of an Alloy power head.", the answer is yes. In fact, its not a question of 'could', its a confirmed 100% it will.

This is why outboards have sacrificial anodes. The sacrificial anode corrodes before the expensive bits do. Once the anode corrodes sufficiently, the other bits will start corroding.

I wonder how many here realise there is anodes bolted into the powerhead of most outboards to deal with this problem?

It's not confirmed at all. If the SS prop was an issue you would expect to see corrosion around the leg adjacent to the prop and linked by seawater (electrolyte). The anodes are there to protect from corrosion in general (which can take many forms) and not specifically to protect from aluminium props.

[scottar]

Actually Scottar, I misworded, I meant Zinc oxide rather than ally oxide, but I think you know what I meant, anyway, no, the boat was locked up everything was switched off, batteries isolated and no shore power. However there were a couple of steel trawlers close to my boat and they may have had their generators running or shore power connected. It just seemed puzzling at the time and since it didn't reoccur either due to me earthing everything, or by the fact I never moored there again so I didn't worry about it any more. But I do remember that the guys in the States had their legs severely chewed and pitted made me think that the legs may have been made from a bad batch of ally alloy, I would assume that they had anodes on their legs as well, so maybe those got chewed off quickly like mine without the owners knowing, which left the legs unprotected.

Everything I could find with regard to electricity causing the issue revolved around the boats all being connected electrically via the earth connection. Without being connected to shore power it should not have effected your boat. I have heard of anecdotal reports of large steel boats accelerating corrosion. It can be a dark art chasing this sort of thing.

[Bobpen]

So get a bigger jar and put the whole motor in if you don't want to take the prop off. Do I have to think of everything Bob??????

I only use my boat occasionally .......... you got me there. The rest of the time I have to work..........maintaining a fleet of commercial vessels..............made up of dissimilar metals including aluminium, steel bronze, stainless, copper nickel, cast iron and probably a few others.............that get stored in a giant puddle of electrolyte..............by changing the anodes which protect them against galvanic corrosion among other things...............who would have thought huh.


You are right though Bob........some people do get confused easily.
How many of your commercial vessels have fresh water cooling. Why is that?
One of the trawlers we chartered had a 75 year old WW2 auxiliary from a mobile spot light from the Blitz.
The block survived 75 years because it is fresh water cooled. How good is that?
It was stupid to post here. "Did I check the anodes in the power head?" Sure every weekend.
I have worked with boats since 1970 .
I have seen lots of galvanic corrosion but not in the 18 or so outboards I used because they have anodes.
I had an 1 HP agitator for a seawater pond that ate anodes. I bolted a half kilo of zinc to it. That fixed it.
Outboards have anodes. My Etec anodes were only lightly corroded. They were doing something.
I hot flushed the motor after every use with muffs and checked the anodes.
Please let me know what you would have been doing to save this motor if you maintain commercial vessels.
Check inside the power head after use? LOL

[scottar]

How many of your commercial vessels have fresh water cooling. Why is that?
One of the trawlers we chartered had a 75 year old WW2 auxiliary from a mobile spot light from the Blitz.
The block survived 75 years because it is fresh water cooled. How good is that?
It was stupid to post here. "Did I check the anodes in the power head?" Sure every weekend.
I have worked with boats since 1970 .
I have seen lots of galvanic corrosion but not in the 18 or so outboards I used because they have anodes.
I had an 1 HP agitator for a seawater pond that ate anodes. I bolted a half kilo of zinc to it. That fixed it.
Outboards have anodes. My Etec anodes were only lightly corroded. They were doing something.

Only a couple have full keel cooling with no salt water exposure. The rest run heat exchangers which is where the anodes are located because that's where the galvanic corrosion will occur. Same with the gearboxes that run salt water cooled heat exchangers, the oil coolers, hydraulic coolers and so on. Then there are the anodes on the external grid coolers and the hulls themselves, in the sea strainers for the various systems etc. BUT - these are full of seawater 24/7, often let sit stagnant for weeks on end, are never fresh water flushed and only come out of the water every 2.5 years. Do we get galvanic activity - for sure. Does it do damage - you bet if the anodes aren't kept up to scratch. Have we destroyed any equipment from the inside in the ten years I have been with the company - not that I recall. Plenty of stuff has been destroyed from the outside as far as corrosion is concerned but with anode maintenance, galvanic damage is minimal. Some of these vessels are as you say - decades old. At 10 years these systems have done in the vicinity of 85 000 hours in the water without terminal failure due to galvanic corrosion. Galvanic activity is not a new thing. Manufacturers figured out a way to deal with well before you and I were around. They have not found a great way to deal with the other forms of corrosion where a bare metal surface in contact with salt water is required however.

"My Etec anodes were only lightly corroded. They were doing something." Yes they were - accounting for any galvanic activity that occurred. Once the anodes are exhausted, the galvanic activity will attack the least noble metal. Were they exhausted - doesn't sound like it and typical Evinrude outboard usage from my experience would indicate you hadn't done anywhere near enough hours for that to be the case.

"Did I check the anodes in the power head? Sure every weekend." Don't believe I asked that - main reason being I don't believe there would have been any. None in the powerhead of my E-Tec. None in the powerheads of the OMC Evinrudes I owned either. They are all located in the leg.............because that is the place galvanic corrosion normally occurs as it requires the engine to be in the water for it to happen. Your's, like mine, and most other recreationally owned motors on small vessels spent most of it's time on the trailer.

LOOK AT THE TIME LINE - You are telling us your power head was eaten out in effectively 17 days of continuous use. Your leg was the water for effectively 2 months - any corrosion there? It's the same metal with some of it in more or less direct contact with stainless and salt water - bolts, shafts, the cup and plate off your water pump.

Pretty much every commercial motor I have ever seen runs a stainless prop as most are high horsepower - and in SE Qld there are quite a few crabbers and netters that run E-Tecs and they, along with the other brands get literally thousands of hours of actual use without dissolving their motors. There are reports of up to around the 5 thousand hour mark on pretty much all brands of motors these days. The big difference however is time sitting around doing nothing - which is what does the damage due to other forms of corrosion - not galvanic. It's been killing recreational motors for years regardless of propeller choice and will continue to do so until they make them out of something else.

I have no doubt corrosion killed your motor. I have no doubt you are cranky about it - I would be too although I actually expect it to happen to any outboard long term. I also have no doubt that the form of corrosion that killed your engine was NOT galvanic corrosion induced by running a stainless prop. That was a mere co-incidence.

[Lovey80]

Spot on Scott. Its just plain dumb you had to write all that. The prop>Galvanic corrosion argument is so dumb many readers thought Bopen's posts about it were a piss take. The sad thing is, even with all the more plausible explanations outlined, I think he thinks his prop ate his block and his stainless prop shaft on his new engine won't do the same thing. just dumb dumb dumb.

[TheRealAndy]

There are plenty of different types of aluminium corrosion Aluminium Corrosion | 13 Types Explained | Fractory (https://fractory.com/aluminium-corrosion/)

You can roughly break that down to 2 types, electrical and mechanical.

No one here has any idea what actually happened because no on here has actually investigated what the problem is,

[scottar]

[QUOTE=Bobpen;1687044
Please let me know what you would have been doing to save this motor if you maintain commercial vessels.
Check inside the power head after use? LOL[/QUOTE]

Exactly what I have done with all of my own outboards through lessons learned one way or another. Flushing with fresh water alone will not remove all traces of salt. It is this salt that will set up corrosion inside an outboard powerhead causing pitting that will ultimately eat it's way through the water jacket right where your boat spends most of it's hours - on the trailer at home. Anodes will not protect under these circumstances for obvious reasons. I have always flushed with either a non corrosive detergent formula or in more recent times, a dedicated flushing solution. Periodical running of the motor even when not in regular use is also a good idea. Periodical inspection under the thermostat covers and through any anode orifices (if your engine has them) is also a good idea. I would be doing it with your new motor too Bob.

Check inside the power head - yeah great idea if you are up for it and have the skill set - periodically - and every so often we have to do just that as requested by the surveyors. Borescopes, removal of coolers for inspection and cleaning, random removal of heads and eventually full head removal for inspection and rebuild as recommended by the manufacturer. We have diesel mechanics completing a full head removal and rebuild at the moment on a pair of Cummins V16's amongst other projects. - over $100K at a guess I've been told to spend on maintaining running engines - not replacing them..........LOL ;D

[scottar]

You can roughly break that down to 2 types, electrical and mechanical.

No one here has any idea what actually happened because no on here has actually investigated what the problem is,

Yep. Most corrosion is an electrochemical reaction. The different types relate to cause - not effect.

What actually happened - perhaps but given what Bob has told us over the three threads on the same topic, and the characteristics of galvanic corrosion, with what you know about electricity and electron movement do you honestly think it's potentially galvanic corrosion Andy?

[Bobpen]

I'm not stupid at all - in fact I'm a qualified chemist. Check what happens when you drain the bath or sink next time. Water has a low viscosity and has the property of surface tension. It we bead into droplets rather than form a continuous film.
My kitchen sink has a film when I drain it because I don't use Rainex on it.

[Bobpen]

Now this is the 2nd time you have mentioned "offshore projects" , please let us know what these are, they might add some credibility to your statements so far they have NO credence according ti current scientific knowledge.
What you have probably not realised (about as polite as I can say it), is that many members on here come from some very diverse backgrounds. Whether it be as simple as massive hrs on the water, to people with an enormous scientific and engineering background.
Many have been on this forum for quite a long time and kept their background quiet.
Bobpen, you are spouting in my very humble opinion a lot of garbage and are just stirring the pot. I did say previously that I wouldn't post any more but you did get my goat up. This is my last offer on this subject, pxxs off and let things lie, agree to disagree with everyone , you are $16k worse (probably better) off with a new motor. Go fishing or whatever you do and let the rest of us think about things that really matter.
Since YOU asked: At the Mariculture faculty where I worked we had onshore sand filters on the land and offshore filters in the bay. They are marked by the yellow buoy off Cleveland Point on the way to Horse Shoe Bay.
Another "offshore project" was scuba diving to service current meters deployed in the middle of the Gulf of Carpentaria.

[billfisher]

My kitchen sink has a film when I drain it because I don't use Rainex on it.

I find that hard to believe, especially the vertical surfaces.

[Bobpen]

Only a couple have full keel cooling with no salt water exposure. The rest run heat exchangers which is where the anodes are located because that's where the galvanic corrosion will occur. Same with the gearboxes that run salt water cooled heat exchangers, the oil coolers, hydraulic coolers and so on. Then there are the anodes on the external grid coolers and the hulls themselves, in the sea strainers for the various systems etc. BUT - these are full of seawater 24/7, often let sit stagnant for weeks on end, are never fresh water flushed and only come out of the water every 2.5 years. Do we get galvanic activity - for sure. Does it do damage - you bet if the anodes aren't kept up to scratch. Have we destroyed any equipment from the inside in the ten years I have been with the company - not that I recall. Plenty of stuff has been destroyed from the outside as far as corrosion is concerned but with anode maintenance, galvanic damage is minimal. Some of these vessels are as you say - decades old. At 10 years these systems have done in the vicinity of 85 000 hours in the water without terminal failure due to galvanic corrosion. Galvanic activity is not a new thing. Manufacturers figured out a way to deal with well before you and I were around. They have not found a great way to deal with the other forms of corrosion where a bare metal surface in contact with salt water is required however.

"My Etec anodes were only lightly corroded. They were doing something." Yes they were - accounting for any galvanic activity that occurred. Once the anodes are exhausted, the galvanic activity will attack the least noble metal. Were they exhausted - doesn't sound like it and typical Evinrude outboard usage from my experience would indicate you hadn't done anywhere near enough hours for that to be the case.

"Did I check the anodes in the power head? Sure every weekend." Don't believe I asked that - main reason being I don't believe there would have been any. None in the powerhead of my E-Tec. None in the powerheads of the OMC Evinrudes I owned either. They are all located in the leg.............because that is the place galvanic corrosion normally occurs as it requires the engine to be in the water for it to happen. Your's, like mine, and most other recreationally owned motors on small vessels spent most of it's time on the trailer.

LOOK AT THE TIME LINE - You are telling us your power head was eaten out in effectively 17 days of continuous use. Your leg was the water for effectively 2 months - any corrosion there? It's the same metal with some of it in more or less direct contact with stainless and salt water - bolts, shafts, the cup and plate off your water pump.

Pretty much every commercial motor I have ever seen runs a stainless prop as most are high horsepower - and in SE Qld there are quite a few crabbers and netters that run E-Tecs and they, along with the other brands get literally thousands of hours of actual use without dissolving their motors. There are reports of up to around the 5 thousand hour mark on pretty much all brands of motors these days. The big difference however is time sitting around doing nothing - which is what does the damage due to other forms of corrosion - not galvanic. It's been killing recreational motors for years regardless of propeller choice and will continue to do so until they make them out of something else.

I have no doubt corrosion killed your motor. I have no doubt you are cranky about it - I would be too although I actually expect it to happen to any outboard long term. I also have no doubt that the form of corrosion that killed your engine was NOT galvanic corrosion induced by running a stainless prop. That was a mere co-incidence.
In the early 70s I used to use a De Havilland River Truck with a Hamilton Jet and a 250 Falcon car engine.
The only marinization the car engine had was a heat exchanger and WD40.
The jet unit had a take-off to feed the heat exchanger.
No corrosion problems at all.
One of the trawlers we chartered had keel pipes. When they leaked someone snorkelled down and patched them with epoxy putty. Easy.
Britney Spears could be posting here. I like to give some background.

[Bobpen]

I find that hard to believe, especially the verticale surfaces.

Look in your sink after you have used detergent.
or: Have you heard of biofilms?
I have.

[billfisher]

Look in your sink after you have used detergent.
or: Have you heard of biofilms?
I have.

Detergents actually break up the surface tension. And what is the relevance to your outboard motor? Or that of biofilms, other than you having a very grotty sink?

[scottar]

Bit of research follow up.

Christian Vargel, in Corrosion of Aluminium (Second Edition) (https://www.sciencedirect.com/book/9780080999258/corrosion-of-aluminium), 2020
13.7.4 Distance from the contact zoneGalvanic corrosion is a local form of corrosion. It is limited to the contact zone. The intensity of corrosion decreases rapidly with increasing distance, even by a few centimetres, from the point of contact between the two metals. This decrease is greater when the electrolyte is a poor conductor.
This type of corrosion is so localized because of electrical reasons. Electrical current flows according to a path as linear as possible. Since galvanic corrosion often tends to develop at depth, it is not uncommon that galvanic corrosion perforates parts several millimetres thick.

"Christian Vargel has over 50 years’ experience in the corrosion and metallurgy of aluminium. He was chief engineer at Pechiney which was the European leader of wrought, extruded and cast aluminium products – where he primarily focused on corrosion of aluminium alloys, from a practical perspective."

[shakey55]

This appears to be going nowhere. Although everyone agrees that there can be Galvanic Corrosion in boat parts, you will not convince the group here that your SS prop was responsible for the destruction of your outboard motor.


It’s more than likely bad luck or poor maintenance.

We all feel for you, having been forced to replace the outboard at a cost you were not expecting, but I do think it’s time to give it a rest and move on.

If you don’t let it go, it will eat away at you like Galvanic Corrosion.

Good Luck Bobpen


Sent from my iPhone using Ausfish forums

[stevej]

Annodes can also be coated with minerals that require them to be removed and scuffed up or cleaned to work

the dams I fish are full of heavy minerals and that also means the towns water is heavy and full of calcium mainly
when flushing a residue gets left everywhere and is just as much a concern as salt water for me here

destroyed the paint on my classic cars with enamel paint also Etched the windscreens of our cars requiring replacement at 5 yeas old
plenty of reasons for things to fail most are maintenance related as is probably the case here

[Dignity]

Yep, my mechanic removes all the anodes at service time and cleans them, especially any mating services.