Sail Life - Hauling out with a nasty surprise 😬
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- Опубліковано 5 лис 2022
- We go up on the hard an find a nasty surprise.
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Just got to the end. The stainless part corroded due to crevice corrosion. Crevice corrosion occurs when the stainless steel is exposed to anoxic water. Passivation relies on an oxidizing atmosphere (or solution) to form a thin passive layer on the stainless. If the atmosphere (or solution) becomes reducing instead, the stainless may lose its passive layer and get corrosion that looks just like that... like black rotting that penetrates the whole piece. It seems possible that a zinc could help de-passivate stainless. I am not sure. But the real fix is to make the shoe out of bronze (NOT brass... proper bronze alloy for below the waterline parts). You can protect the bronze with a zinc. Bronze is not subject to crevice corrosion. The zinc is just to protect in case there are stray currents in a marina. This is my opinion. I am not an expert either, but I have been around the block a few times. Stainless is actually a terrible material to install below the waterline. The other place you get severe crevice corrosion is on the prop shaft where the cutlass bearing is, or going through the stuffing box. Prop shafts are (or should be) made of special alloys that are less subject to crevice corrosion.
Maybe just a nerdy idea: What about 3D-printing a rudder shoe out of carbon fiber reinforced polymers? Just as a (temporary) replacement in case the stainless shoe gets too corroded for whatever reason when you cross the atlantic. They don't weigh much, and would be some spiffy new technology to master for Mads and Ava.
There might be some space left in the technical compartment for a 3D printer. Hint hint
I agree about bronze. There are plenty of places in the states that will cast these in bronze using your stainless part as a pattern. Or simply weld them up from bronze plate.
Titanium perhaps?
@@nutsandbolts432 I don't know a lot about titanium. Maybe it would work also. But bronze has been used for many 100's of years. We KNOW it works. A bronze shoe will last for the life of the boat as long as it is not subjected to severe galvanic corrosion somehow (such as can only really happen in a marina with large leakage currents).
Your stainless shoe could be a real dog's breakfast of different alloys. The base metal weld filler, washers, bolts, and nuts could all be a different alloy. I only know to use 316 on a boat. Even then you can change the alloy by welding. My prop shaft seems fine with zinc protecting it but you have a copper coating to further complicate things. I would recommend changing to bronze if possible. If not that then make sure everything is 316 alloy and the fabricator knows how to compensate with proper filler metal and also properly pickle the welds. Best of luck !
Counterintuitively, stainless steel under the waterline in salt water is more susceptible to oxygen pitting and crevice corrosion specifically due to the low oxygen environment.
That is basically the smoothest and easiest-looking prop removal I've ever seen. Well done with whatever you lubricated it with at assembly; this is DEFINITELY the desired result.
If it happened ones, it will happen again if nothing has been changed. You should prepare / order the same shoe out of bronze with bronze fasteners next time you go out.
He has a stainless steel rudder structure...
I assume the corrosion was from mixing ferritic stainless and Austenitic stainless... It would explain the washers being basically gone. Probably acted like an anode
The problem is that if the box says A4 quality you have to trust it. There is no way you can tell the difference between a A2 and A4 quality Washer by looking at it. Probably the washers were A2 and maybe the bolds as well.
I would agree but I have through work seen so called 316 stainless sold with forged material certs. When it was checked using a PMI (positive material identification) tool it didn’t have the required amount of Chromium. I suspect something isn’t the right stuff probably the washers as you say
Looking at the surface that was under the washers, that seems quite possibly the explanation.
It would be helpful to see the washers as well.
I’ve seen similar issues when 304 and 316 have been mixed together in an assembly. When that situation occurred, a new set of nuts, bolts and washers were used on a stainless ‘P’ bracket fixture. Turned out that the bolts were the odd ones out, though the washers took the brunt of the corrosion damage. 🤷♂️
@@PaulM-ls6qj Magnet.
Thanks, also the use of Tefgel, when reassembling, to help prevent galling of the threads. I found that out when working on a mine water system.🤦♂
I’d change the angle of the clamshell. As the boat goes down in the water you will get pressured water forcing its way into the locker. Pointy bit should be forward and the hole back, to create a suction/low pressure as you move forwards and help to empty the locker of any water.
That's my thought, especially when an Atlantic crossing is on the schedule.
Agree 100 %
Yes, it's streamlined for a reason.
yes !!!!
Great minds think alike.
With pitting, its defenetly galvanic corrotion. Insulation from other metals is a must. Coppercoat, carbonfibre, may be the culprit.
I’ve seen that type of corrosion before at work on sailboats and motor yachts on drive and steer components and it’s typically caused by using an aluminum anode opposed to a zinc anode. Another common cause is mixing two different types of stainless together such as mixing ferritic and austenitic stainless together. It’s very common for this to be overlooked. In your case I think those washers were a different type of stainless and the anode was NOT at fault. I would just keep an eye on it when you clean your hull.
Can’t believe it has been two years. WOW! Great job you two 👍
Copper fouling is an electric conductor the stainless steel is not isolated
Have you been close to an steelboat for a longer period? Galvanic corrosion is always an electric problem. No matter if the source of the current is inside the boat or outside on another one. Even steel pillars in the water can cause such things. But only if you are close to it for long time. Seems you need to put some extra anodes on the rudder. For bigger ships there is an calculation process we need to deal with for class requirements. Just wanted to mention that it's not that of an easy deal.
Thanks for mentioning the cost for the haul out and the anti fouling,. Very few youtubers do that and stuff like that interests me.
You should paint a pinstripe on the topsides both in that indent & above the waterline, would make her look a lot sleeker in the water as optically it will make her look less high!
I think the boat used to have those and Mads specifically took them off, as, in addition to his own opinion, the feedback by a majority of (commenting) viewers at the time supported that. Personally I wouldn't have taken them off, but now that they are gone, I probably wouldn't put them back on unless a big repainting was being done.
@@sleepyjesus7265 I think he should not put the same ones back on, maybe more thin/ modern line, as I agree that the original stripes are a bit outdated
Agree. A sheer stripe and boot stripe would definitely make it look sexy and less boxy. And probably faster too😉
@@garysouza2277 I've gotten the impression that Mads and Ava don't quite value speed that much. They probably couldn't handle the excess thrust the stripes would yield.
nooo the clean look is modern and makes her look like she has more freeboard
it's great to see proof that your 'somewhat extensive refit' is doing very well indeed.
Could be an interaction between the coppercoat and the stainless. Interestingly had this happen on land! A fern frond created a bridge (when wet) between a steel roof designed for coastal use and a copper gutter, the corrosion on the steel was rapid!
Try painting under the shoe with epoxy to isolate it from the copper coat.
Or bedding it in butyl.
@@wallacegrommet9343 had already bedded with Sika-flex, thats the black residue you see under the shoe.
I missed that, obviously. Thought it strange that Mads hadn’t bedded the piece! Turns out he had.
hi Eva and Mat!
If i understand the corrosion problem correctly, you have an "electrically isolated" metal object surrounded by a copper coat layer (conducting), fastened with with a different type of stainless metal and a peace off zink for good measure. All this is in a salty fluid (saltwater) with a possible current when in you are in a harbor. Basically a battery. The reason is the obviously the mix of the metals. craves-corrosion is one of the typical signs for electrical-corrosion. That is at least what my teachers used to say. Isolate that thing from the conducting hull, connect it to one other BIG stainless (ruddershaft) element on the boat to widen the surface area and do not mix different stainless metals, and you should be fine. You can cover the stainless with paint as well, but stainless is known for inter-metallic corrosion, hinds the craves-corrosion.
p.s. love your show, i watch it regularly and like it very much!! best reg. A.
You have done a wonderful job renovating Athena. I'd suggest that you get around to adding a boot stripe at the water line. It does two things. it gives you a more noticeable means of telling at a glance that your boat is riding at the proper level. If you add two or three 1" stripes an inch apart, it provides a visual ruler to determine just how far down in the water it has settled. I have walked marinas enough to have seen two boats who were slowly sinking and was able to notify the marina manager. It can help you manage your weight and balance as you begin loading it up for a long passage with extra ice cream. ;) Boot stripes and cove stripes can give the appearance of a shorter freeboard and longer hull. A rub rail can be partially camouflaged in a dark painted cove stripe.
As far as I know you should never ever use stainless beneath the waterline. Stainless can corrode. It is a mixture of different metals and in seawater beneath the waterline you get electric corrosion because of the metal mix. Better use galvanised steel or cast iron. The very best would be bronze.
I wish I’d paid attention in Spanish class too. I didn’t know we had so many Hispanics in Texas (I lived in a small town surrounded by small towns)…live and learn
Safe travels for both of you!
Believe I had a post on AISI 316L and A4 to you a few years ago. Don't think you liked the ideas. But I am a corr. engineer. Consequently on my boat soake in SW you will not find A4 bolts and absolutely no AISI 316L not supported by catodic protection system. This is exactly what you expreience now. You may send me an mail, in Danish. Whish you all the best.
The hull definately needs horizontal stripes which will make it go faster & make the sailboat look infinitely spiffyer.
I thought they had to be red to make it go faster. I just dont think any other color has the same performance credentials.
@@philgray1023 Gold is the way to go! Shows a certain flare or is that spiffyness? It is possible to buy sticky back coloured tape for that very use.
@@rogerdinnis3816 it should be navy blue, just like the rest, would look so much cleaner
Whatever color they are, it was going entirely too slow on that travel lift. Racing stripes required.
@@philgray1023
I noticed that some X-Yachts sailboats which I think are civilised performance sailboats have as many as 3 boot stripes that appear to be a shade of red?😂
Great video Mads, I had a great moment of nostalgia when you got up on the hard and started some DIY!
About corrosion: if there is no electrical contact, the problem boils down to the fact that two metals, separated by a dielectric material, inserted in an acid or saline medium, transfer of electrons occurs. Even though the screws are made of steel and the "lock" is also made of steel, they have different compositions, so there is a potential difference and, consequently, corrosion.
Hi Mads,
I might call myself an expert in corrosion. 😅
1. Zinc will never have a corrosive impact on stainless steel. Zinc will sacrifice itself in favor of the stainless steel.
2. 316 stainless steel covers are wide range of stainless steel alloys, not all are suitable for marine environments. That’s what I think is your problem here. Stainless steel suitable for marine environments are called duplex stainless steel. If your stainless steel guy will make the rudder shoe out of duplex stainless steel, I can guarantee you, that there will not be any issues.
Best regards from Denmark,
Philipp
sailing dauntless had a similar issue with there sail drives and the cause was electrical current coming from the shore power connection leaching off current into the water
The first expert was right about the zinc being the problem. With no connection to an electrical system the zinc and stainless act like a small battery where both metals lose some material creating electricity that is discharged into the water. You can test this by connecting the leads of a volt meter one each to each type of metal while its in salt water. It should show 0.7 - 1.4 volts, maybe more. If the stainless is completely isolated from other types of metal and electrical it does not need a zinc. No dissimilar metals, no dissimilar metal corrosion. No current path, no electrolosys. Crevice corrosion may still be a problem.
Great video guys, perfect for every Sunday evening.
Can't believe its two years since she went in the water, still looking good.
thanks for the update and glad all was taken care of. i hope you can solve the rudder shoe problem. and please have a great week ahead see you on the next video
Beautiful yard. The boat looks very lovely
Spiffy work and thanks for a great Sunday viewing as per usual best wishes Mark
quick in and out, great update 2x👍
It good to see all the thingies out of the water
Another great video Ava and Mads .
It's galvanic corrosion caused by a charge in the water. That it's not connected to the rest of the boat ground system is the problem. I had the same problem on a stainless valve that was entirely isolated from the rest of the ground bonding system. The charge travels through the water, and starts eating the metal. Check the whole rudder, and make sure it's bonded to your ground.
Good luck on the prop coating by the way. I was not impressed with mine. It wasn't completely useless, but from the sales pitch, I was expecting at least a solid year out of it.
A definite conundrum I'm sure that you will figure out. She looked beautiful lifted out of the water great job on everything I like the new chartplotter holder. Thanks again for sharing your lives with us ✌🏼💗😊❣️
Would a cork or a rubber nub be good on that new cleat in the cockpit? It would be annoying to be in a storm and get thrown sideways and get a jab from the top half somehow.
Mads Hi. The corrosion looks like crevis corrosion. The plate looks like it and the washers had water trapped underneath in a low oxygen situation. The black staining that is around the shoes "holes" or damage is typical of crevis corrosion. The washers also look like they have a similar issue. A4-70 grade bolts and washers can be 304 or 316 Stainless Steel. In this instance youu would want to be sure that you have 316L fixings and that no water become trapped or not moving lowering the oxygen content to cause the corrosion. There is an artical on our website that includes this kind of failure issue. Sail Safe Guys, Ant & Cid.
One source of corrosion is when you are tied up in a marina and sharing shore power with other boats. Not that you actually "share" the power, but you are connected to the same electrical system. Even if your boat is perfectly fine and insulated you might act as a suffer anode due some other boats inferior insulation. I experienced this on my prop and zink anode after a season doing the Göta Canal.
Hi, we're all learning along with you, for you rebuilt Athena and the sea is trying to eat it. Fair winds, safe sailing and catch you both on the next one. Thank you 😉👍for your video.
Love your channel!
The conclusion therefore reported to the Admiralty in 1763 was that iron should not be allowed direct contact with copper in sea water.
Great video and I can't wait to hear about the solution when its discovered. I would agree the rudder shoe may be better suited to be made out of bronze.
Hi Mads, It reminds me of some 'This Old Boat' sections regarding stray current. I first though of a difference in potential between the rudder and the rest of the boat (as the rudder is not grounded). Another lead to dig may also be the way the grounding is done while connected to the grid in a marina (earthing and current coming from other boats, corrosion section p309).
You need a folding propeller!!! Being Danish a Flex-o-Fold is the obvious choice - I had one on my previous boat and it was a thing of beauty!!! It completely transformed my boat after replacing the fixed three-bladed prop with no negative side-effects!!!
Great vid. Thank you. Greetings from Spring Green, Wisconsin USA
As others have suggested the issue with the stainless shoe corrosion is the coppercoat. In the same way that metal skin fittings should be isolated from coppercoat you need to ensure the stainless steel is totally isolated. I would correct ASAP.
Mads, every international sailor I’ve talked to states that the quality of workmanship and the prices are better in European boatyards than in the US. My sample set is small
(about 10), but they were all emphatic.
Absolutely terrific video in letting me understand what your issues have been and sharing your outcomes. The two of you are special! If you come to US, Hampton, VA I have a guest dock at my house for you!!! Sailing La Vagabond stayed here in 2019. Wayne McPhail
i refuse to believe that Athena has been in the water for TWO YEARS already ... was it not just yesterday that you put her in? OO
When reversing a long keeled yacht I have found it helpful in the past to gun it briefly in reverse then shift to neutral and steer while coasting. It worked well for my traditional William Garden 33 timber yacht.
Make one of the bolts on the rudder hinge longer and fit a anode to it if the problem persists. Orherwise a zink coating might last a little while too.
Great video
It might be worth checking the type of stainless steel: bolts/washers against the SS bearing holder (shoe). 304; 308; 316L or similar have different electrolyze corrosion resistance and might do a couple in the saltwater environment, as they are close to each other. The losing metals are bolts and washers, change them for 316L from a guaranteed manufacturer. Sail safe Rds
Relative motion between the various components would wear away the passivation layers of the stainless and accelerate the corrosion as well.
Copper coat is setting up circuit, ground rudder bolts, or copper coat
My understanding is that ALL conductive components below the waterline must be electrically bonded to establish a common potential. When all components are not bonded together, there will inevitably be dissimilar potentials, and therefore localised galvanic corrosion. Since you are already back in the water and effectively still have the same ‘circuits’, next time you dive, use an extension wire and a DVM to measure the voltage between your problem component and the other anodes/bonded components. If you have a voltage difference, then that’s the problem.
Still overall looks like a win, win haulout. Stay safe and we'll see you next week.
Quite frankly I've worked pretty damn hard at solving this low oxygen crevicing problem. Sometimes I can find extremely small ( invisible) pin hole tunnels under a high pressure test.
I was losing the battle at every annual. Things like anti seize definitely increased the problem. Never use silver grey or copper. Use this: I finally got a grip by literally slobbing on, into, and all over with a thick sticky moly grease. It should be black and really messy staining in nature. Somehow it helps to slow the low oxygen or active passive dissimilarity within these noble alloys.
On this rudder I would also look for NAS bolts, washers, and nuts. National Aero Space hardware is the highest grade money can buy. Second choice would be a Mil Spec or AN grade fastener.
Good luck!
Athena is looking really good for two years in the water, a tribute to you and copper coat. Prop speed works really well on our part of the east coast of Australia so I am looking forward to seeing how the alternative coating endures, it looks pretty much identical. Looks like a classic case of crevice corrosion on the stainless rudder shoe , I would be inclined to change that for bronze when you get to the US.
Yes... sanding
I was always told to not use stainless below the water line because the lack of oxygen causes it to corrode and to use bronze instead. Stainless for above the waterline.
I would just try one of the suggested option for the corroded rudder shoe: put the zink anode near it, but not on it. Then check it again after a year. If it's still coroding, then there might be some way that there's an electrical connection...
I use Prop Speed every two years on my prop and shaft. It is the best I have found.
I suspect that the type of stainless that you asked for and then paid more for wasn't what you got either for the shoe or the bolts and you had a differing metal corrosion problem
Hi Athena, we have used pellerclean in the Med before and we got good results with it. Once every two or three years a new coat. It lasts. The rudder looks very much like elektrolyse due to different potential of the metals used. Very difficult to asses what did the trick. The bolts or the rings or something else. Try to use best quality 316 stainless. Lucky it did not pitted the rudder shaft itself. You also showed you use normal anti fouling over the sail drive. If there is any copper in that anti fouling that is also tricky and could pit the aluminium casing of the sail drive. It is not recommended, even with a primer in between….. Greetings Ruben
Nice video. Reminds me of the "Good old Days!" Best regards
Some good opinion in the comment on SS below water line. BUT surely the shoe IS connected to the rudder shaft and that is connected to the steering that is all sorts of metal , cables etc etc
Cheers Warren
Forget all the comments about CopperCoat. CopperCoat doesn't work like people think it does, it's non conductive. FWIW, I agree that this is most likely crevice corrosion, these items are as someone else pointed out, most often made of bronze for that very reason.
hi mads, another excellent blog. back ln the day i worked on fit out for a leading boat builder, and we always used bronze shoes and fixings on all our rudders. i never heard of any corrosion problems. hope this is some help.
It's just possible that the shoe being so close to the stainless rudder post in a conductive medium of salt water, and the post connected to cables and auto steer components, there was enough transient voltage leaking into the shoe to eat it. If you have any prop coating left over it might pay to coat the stainless with it to help isolate it...
Hi if all else fails try looking to see if the rudder post etc.... is connected electrically via the steering cables and quadrant if nothing else.... and of course at the wheel end you have electrical gear....you may find moisture ingress in the electrics has caused a current path causing the stainless steel degridation.... an insulation resistance test could show that up, and help resolve the problem especially if it is your rudder getting an imposed current in relation to your zinc and propeller.
You should not need to haul out to test the insulation resistance....just test the electrical circuits feed to anything attached to the steering assembly such as nav system, compass light etc by isolating both positive and negative of each of those circuits......in fact as I'm writing this I'm realising the video will have screened coax which will be a connection.... good luck
Have you looked closely at the propeller hub rubber bushing , it looks like it has failed, these 3 blade Volvo props are renowned for premature failure. ?
I was surprised to see how you attached the clam shell cover. I always thought a clam shell cover pointed in the direction of the water flow and not at the sky. Since it’s purpose is to direct water past the hole. Not to mention the aesthetics… It looked extremely odd to my eye. You must do things differently in your part of the world. : )
Really looking forward to finding out how the prop treatment works. Always a problem for me. I really enjoyed this video...thanks!
Parts do not need to be connected to each other by line to be exposed to the processes of corrosion. In sea waters they are connected automatically because sea water is electrolit. It exactly what happens in a battery.
So satisfying to see the haul out. And how much you care for her.
Not all stainless is equivalent, even when it says it is... We've have 'guaranteed' 316 hose clamps fail at the screw, because the screw was from a different supplier. We've had 1000m pressure rated wet connects fail at the 316 fitting because the male end was isolated from the case (which had zinc placed far more regular than necessary) and the two parts, though both very expensive 'guaranteed' 316, were just "ever so slightly" not... If there is any dissimilar metals, the ocean will make a dielectric of some potential. Use teflon spacers and coated fasteners, the cheap route, or source all metal from a supplier that guarantees the steel properties. That used to be easy, but now you have to verify (going back to the hose clamps, same US vendor for years, then all the sudden). Or, just bite the really big bullet and use titanium everywhere!
I have heard that isolated bits can have problems when some other boat has electrical issues nearby. The solution I have heard is to add that bit to the grounding system. Consult an expert, but this might give you a place to start.
I have an Island Packet with a ss shoe from the end of the keel to the bottom of the rudder. It is essentially isolated electrically from the rest of the boat and has its own anode. So a very similar setup. And I had almost identical erosion to you with the threads on the fasteners being almost gone, parts of the heads of the fasteners eroded away and what looked like burnt away tracks in the shoe itself. Iwas told it was electrical erosion and not galvanic action.
Although I've changed nothing it is not getting worse so it's nothing to do with disimilar metals or an electrical problem on the boat. It was almost certainly environmental, probably some dodgy electrical system in one of the marinas between Brighton and Weymouth.
I use Velox on my prop and saildrive leg. I have had no fouling since using this, both in the UK, Med and Carribean.
Serviceable with the repairs, replace in the end.
Every metal below the water line should be bonded. Like all through hull fittings and valves inside your hull. And all inside chain plates.
Another YT channel “Sailing Dauntless” had a corrosion problem where his sail drives were completely corroded to Swiss cheese. It had something to do with being connected to shore power and galvanic reactions.
i got my sailboat with a insulated Backstaye for ssb got it working using a xeigo g90 working like a charm on cb and ham bands
Follow the stainless shaft up to its mounting / Bearings, run a meter from it to battery grd. If you see a voltage continue tracing. Then the tackle coming off the shaft to the steering.
Check your rudder shaft. You may be getting a Electric short though the top of the shaft coming down to the bottom of the rudder shaft.
Check the cables going to the rudder. It can be bleeding electricity from the helm down to your steering that is connected to your rudder shaft.
Just a thought.
So Thank You for a Great video this week.
Until next week Aloha from the Big Island of Hawaii! Aloha
Sikaflex has a good reputation in BC Canada, hopefully that will work well for you. That corrosion on the stainless keel shoe would be a nasty surprise, amazing how electrical currents can form where you don't expect them! I've also read that stray current can be worse in some marinas / harbours where other boats aren't managing their electrical systems well, but I'm not an electrician so you might want to read up on that yourself.
The next time the boat goes ashore, you must measure with an Ohm meter whether there is a connection from the frame on the engine / electrical system down to the two brackets, another thing could be that the stainless steel the brackets are made of is of a quality the bolts
Worth doing when the boat is in the water too. Find things that talk to each other electrically.
And while the auto pilot is on. I suspect this may be adding to the issue.
The stainless shoe/strap isn't isolated as it's connected to the rudder stock which is then connected to the autopilot & steering gear etc
I would be carefully checking the bonding of the steering gear and making sure there is no possibility of a ground loop between those parts and the rest of the underwater hardware (except the saildrive which *is* an isolated system)
I agree with Richard, mixing different SS types, will cause Willy nilly corrosion, it happened to me with my bobstay!
Attach rudder strap to ground through 12 gauge solid copper wire place zinc on top of stainless run wire back to battery ground done deal
Somethings happenning to seawater when it gets hotter. More agressive. Stainless is not a good material. If its passivated it's around copper in the galvanic voltage sequence. If the warm seawater get it depassified it convert into an anode. My own experience with stainless steel parts as nippels and valves is they last about 3 months in the return plastic pipe from seawater coling to buildings. This is hotter than the intake water.
I am surprised when you said Denmark was cheaper than Spain, for haul out that is. I spent a few holidays in Denmark and found it very expensive, but perhaps that was only the beer!
The rudder shoe is connected to the rudder post, which is connected to the bearings, and connected to the helm drive and your autopilot actuator. (reading that is more fun to the tune of the "leg bone" song)
Any dissimilar metals or inadvertent current flow in any of that could set things up for that a reaction at the point.
Agree - Regards
There is a bearing or bushing between the rudder post and the shoe.
@@mckenziekeith7434 That is immersed in saltwater...
I agree it was simply dissimilar materials as the great Rolling Stones once said "You don't always get what you want". Happy sailing
Corrosion is sometimes simple, but is often extremely complex. It can depend on the nature of the "dirt" in the batch of alloy, or impurities, or which end of compositional ranges for a particular alloy specification. Batches are prepared largely from scrap from various sources -- an alloy producer must go to some lengths to produce consistent product, and will dance close to the edge for expensive ingredients, such as nickel That's just one aspect of the problem. I wouldn't hazard a guess, myself, despite having a PhD in Metallurgy.
Regarding the shoe, it does seem like an electrical corrosion. Suggested (reversed) path: shoe