Anchor Chute Steel Delamination?

[Vincentc]

With the anchor chute off, I got a good look at this puzzling deterioration on the stbd side of the chute. It is kind of like a tin can lid which pops up as you are opening it with a can opener. The part that has pulled away is about the size, thickness and feel of a soup can lid. It is metal, not just a coating and the area under the pull away is rusted even though the chute appears to be stainless steel.

Any thoughts on: What this is? _What happened? _How should I repair it?
Thanks,
Vincent
Lilly Marie
43 DC 1983

 

[REBrueckner]

That loose part appears about 1/4" thick in the photos....in any case, unless someone posts a specific remedy, I'd take the chute to a place that welds stainless steel and see what they recommend. It certainly seems like it should be repairable if the chute is all one composition.

 

[Vincentc]

There does not appear to be any strength issue. The frame is about 1/2" thick and the part that has pulled away is <1/32 thick. The pull away part looks like a chrome coating; however it is metal, about the wall thickness of a tin can.
Vincent

 

[yachtsmanbill]

A few questions... is that chute stainless steel? Was it stamped outa one piece or welded from multiple parts. SS is wierd stuff. Ive seen it de-laminated from strain on it, and if thats not the case and it was fabbed (welded) and not stressed relieved, the same thing can happen.
Stainless is great stuff, but if used in the wrong app it can be very granular, and thats kinda what that skin tag looks like... Since its contaminated between the tear, you'd almost hafta acid wash it, then clamp it back into position, and weld it. It'll probably take some finesse grinding and polishing to bring it back to perfect, OR have a welder cut the part out with a grinder and weld a new piece back in etc etc... ws

 

[luckydave215]

That's intragranular corrosion, the part is scrap.
Stainless flat stock is manufactured by rolling, and sometimes the alloy ends up having "layers" of slightly different alloy. This happens through surface oxides being included during the hot rolling process. It looks like a layer cake if you acid etch it and look at it under a microscope.
Why does this happen? Well, wrought stock (stock rolled in air) is cheap stock, the quality control is limited by the required end cost. Better stock is for sale (such as vacuum remelted material) but the manufacturing cost is in line with a part such as a race engine connecting rod or valve spring, not as low tech/cost as an anchor roller.
What all this means, is that the alloy isn't perfectly uniform, and when it is subjected to anaerobic conditions by being bolted alongside another part in the presence of an elecrolyte (humidity is enough), the layers act as a battery resulting in ion transfer between the minutely different alloy layers, and the part corrodes right down the line of different electrical potential.
There's no practical ($$) way to fix a part that has failed in this way, make a new one.

David Malmberg
Development Engineer
Scripps Institutition of Oceanography

 

[Vincentc]

Thanks for the explainations. That is all new to me, and very interesting. It will take me a while to process it.

The roller frame is welded, and certainly looks like stainless; however; the surface looks like it is chrome plated.

I am going to take the frame to a machine shop and see what he thinks. The delamination very thin and the frame is probably 1/2" thick. It looks like a pretty expensive part to replace, on the other hand, a very expensive part if it does break under load.

Regards,
Vincent

 

[luckydave215]

Yeah, it looks like peeling chrome plating in the picture, but it's more likely that the part has been electropolished. Electropolishing is a "reverse plating" process where the part is the anode instead of the cathode. Applying current in the plating bath etches off the surface of the part leaving it with a clean polished surface that looks like chrome. It's a nice look, but the real reason to electropolish is to passivate the surface resulting in greater corrosion resistance.

 

[Brian Degulis]

I've seen that or something like it with ordinary A36 steel plate that was cheap import stuff. If it's the same thing Dave's right there's no fixing it. You can grind it out and weld it but in a short time it opens and starts to peel again.

I don't think it's chrome first I don't think Hat did that. Second chrome would be very thin it wouldn't peel up like that it would just flake off.

Brian

 

[Maynard Rupp]

Tom Slane makes a duplicate anchor chute for all old Hats. He also makes the fiberglass pulpit that the chute mounts in and all the stainless tubing and rub rails to go with it. Give him a call and discuss your problem. He has ready to go chutes.

 

[MikeP]

I like LuckyDave's explanation and Maynard's solution. I wouldn't mess with the existing piece at all, it's why God made trash cans!

 

[Vincentc]

I appreciate everyone's learned comments, and agree with your analysis. But before I ditch an expensive and heavy part (the shipping for a new part could probably exceed repair cost) I'm going to find someone here with knowledge, have him look at the part first hand and get his assessment. Thanks to several shipyards and other local industries we have a number of knowledgable machinist, welders, etc. here and I should be able to locate someone who can look at and touch the part, tell me what they think and with the benefit of your comments I can make a good decision.

Unless Hatteras shows me a record indicating that Lilly Marie was built without a pulpit, I am convinced that this pulpit is original Hatteras. (ie. square drive screws, polyester putty, seamless fit with original hardware, Galley Maid windlass) Did Hatteras use cheap import steel in 1983?

Thanks
Vincent
Lilly Marie 43 DC 1983

 

[MikeP]

Re windlass - not sure if GM is oem or not. At least some boats came with an Ideal windlass. Perhaps they used either one depending on stock or shipping. They look virtually identical (GM copied the Ideal design) though they differ a bit internally - GM omitted a thrust washer that allows an Ideal to power up or down with no issues; GMs are known to fail if used to power down extensively due to the lack of that thrust bearing.