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

  1. #46

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

    Quote Originally Posted by TheRealAndy View Post
    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.

  2. #47

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

    Quote Originally Posted by EdBerg View Post
    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.

  3. #48

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

    Quote Originally Posted by scottar View Post
    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

  4. #49

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

    Quote Originally Posted by Bobpen View Post
    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.

  5. #50

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

    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.
    Democracy: Simply a system that allows the 51% to steal from the other 49%.

  6. #51

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

    Quote Originally Posted by scottar View Post
    There are plenty of different types of aluminium corrosion Aluminium Corrosion | 13 Types Explained | Fractory
    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,


  7. #52

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

    [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

  8. #53

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

    Quote Originally Posted by TheRealAndy View Post
    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?

  9. #54

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

    Quote Originally Posted by billfisher View Post
    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.

  10. #55

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

    Quote Originally Posted by Dignity View Post
    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.

  11. #56

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

    Quote Originally Posted by Bobpen View Post
    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.

  12. #57

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

    Quote Originally Posted by scottar View Post
    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.


  13. #58

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

    Quote Originally Posted by billfisher View Post
    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.

  14. #59

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

    Quote Originally Posted by Bobpen View Post
    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?

  15. #60

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

    Bit of research follow up.

    Christian Vargel, in Corrosion of Aluminium (Second Edition), 2020
    13.7.4 Distance from the contact zone

    Galvanic 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."

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