Sailboat Owner's Guide to Corrosion - Metals Aboard (Collier 8 - 12)

[Will Gilmore]

Welcome to Section 4, the Sailboat Owner's Guide to Corrosion - Metals Aboard (Collier 8 - 12), of our SBO Book club study of Everett Collier's book, 'The Boatowner's Guide to Corrosion".

We are reading and posting, in sections, as we work our way through the subject of corrosion in the marine environment. Each section covers one or more chapters and has been posted in their own threads. As the new threads are started, I will tag any interested participants and create a linked table of contents to make it easier to follow along and participate.

A rough outline of the sections to come are as follows. They may be edited and updated as the current of our discussion requires.

Sections

1. Sailboat Owner's Guide to Corrosion - Fundamentals (Collier 1-4)
2. Sailboat Owner's Guide to Corrosion - Self-Corrosion (Collier 5)
3. Sailboat Owner's Guide to Corrosion - Galvanic and Stray Current Corrosion (Collier 6 & 7)
4. Sailboat Owner's Guide to Corrosion - Metals Aboard (Collier 8 - 12)
5. Sailboat Owner's Guide to Corrosion - Protection (Collier 13 - 15)
6. Sailboat Owner's Guide to Corrosion - Hull and Motor (Collier 16 - 17)
7. Sailboat Owner's Guide to Corrosion - Electronics and Plumbing (Collier 18 - 19)
8. Sailboat Owner's Guide to Corrosion - Topsides (Collier 20 - 21)
9. Sailboat Owner's Guide to Corrosion - Resource

Let me know (@Will Gilmore) if you want your name added to this list. It will appear at the beginning of each new thread to let interested members know when the new thread has opened. You can then post something or click the [Watch] button to follow the thread.

Tagged participants:
@Will Gilmore
@DArcy
@mermike
@jssailem
@dlochner
@dLj
@JamesG161
@ontherocks83
@rgranger
@Mark Maulden
@Davidasailor26
@LeslieTroyer

I'll be happy to edit/update this list at any time.

Some basic rules for maintaining useful and topic focused discussion:
SBO is a public forum, and as such, anyone interested, is welcome to participate, ask questions and express their opinions. There are limitations to the form these expressions can take and the culture of participation. All the basic forum rules of decorum and good manners apply. As a participant in this series of discussions, we would ask that participants remain on topic and refrain from derogatory language or remarks. The express purpose of this series of threads will be to understand corrosion in the marine environment using Collier's book as a guide. We therefore, expect participants to make an honest effort to read and stay up on the material under discussion. We are a group of congenial sailors with a sense of humor that often can run astray. A playful comment on occasion is expected, but anyone of us will feel free to firmly redirect anyone back to the subject at hand if it looks like it is in danger of derailing the discussion. A moderator will be asked to intervene, edit out any inappropriate comments, and possible ban an offending participant, should the group find their continued presence a serious distraction. Posting in this thread will be considered agreement to these terms. Thank you so much for your understanding and cooperation. I look forward to being part of the amazing community that is developing around this subject. I know we will all have a great time.

-Will (Dragonfly)

 

[dLj]

Collier goes through the various metals in these chapters. In chapter 8 he addresses the ferrous alloys. For the most part, in the sailboats we are running, we pretty much use the stainless steels, unless someone has a steel hull boat. That happens to be my favorite hull material, although I don't own one currently. That is the primary hull material I will be looking for in my next boat. Collier makes one notable mistake in talking about corrosion of cast irons in that he says in grey cast irons you get degraphitization. It's actually the opposite, you get what is called graphitization. He touches on HSLA steels, an interesting subject but I'm not aware of these alloys being used much, at least within the recreational boating world.

He brings in the stainless steels, which are used quite a lot in the recreational boating world. He talks about the Martensitic, Ferritic, Austenitic and Duplex grades, but completely misses the Precipitation Hardening grades. This is too bad as they are used quite a lot. The more common precipitation hardening grade of stainless steel that I've seen used is 17-4 PH. It is a high strength, high corrosion resistant stainless steel used a lot the hardware used especially on sailboats. The quick release shackles we use are often made from 17-4 PH stainless steel. I personally won't buy a shackle unless that is the alloy it is made from. These are also often made from 316, but 17-4 PH is notably better choice for this high performance component.

His chapter 9 is on aluminum and it's alloys. We certainly have lots of that on-board. Most of us had aluminum masts, unless we have wooden masts. There is actually a lot to be said for well made wooden masts. However, the aluminum masts are much easier to take care of. I've seen high-performance blacks made with aluminum components as well. Aluminum hulls are quite nice but pricey...

Chapter 10 talks about nickel alloys. I've personally only worked with the Monel alloys in boating. But have pinned for some of the Hastelloy or Inconel alloys at times... They are amazing alloys! These alloys are certainly high performers!

Chapter 11 talks about the copper based alloys. All of these are used in various parts of our boats. Collier says he's a fan of the bronzes, I must say, they are beautiful on a boat!

Chapter 12 ends this section with other marine metals. I find it interesting that hot dipped galvanizing is no longer extensively used. It is a fantastic way to use steels in the marine environment and keep them from corroding for long lengths of time. Standing rigging used to be found made from hot dipped galvanized steel wire rope and frankly, it's still a good choice, although getting more difficult to find. This subject has produced some serious flame wars on discussion groups. But this is not meant to start a discussion on this subject, it just caught my eye reading through these chapters. Collier briefly touches on titanium alloys. And he adds in carbon-fiber composites at the end of this chapter.

Anybody got comments/questions on these chapters?

dj

 

[Will Gilmore]

I have just read through Collier's chapter on iron-based materials. There is a lot to digest there and I'd like to get more familiar with this group of chapters because I, like dLj, am interested in steel construction. As part of the discussion on marine corrosion, just beginning the general concepts seems enough.
-
When I bought my Mariner, the cast iron centerboard was pitted heavily under its very worn coating of bottom paint. There is a brass ring insert at the pivot point and the board hung on a heavy (1") brass pin with a steel cable for raising and lowering. Typical, I think. New Mariners built today by Stewart Marine out of Rockland Maine, come with glass centerboard.

My Mariner spent most of its days in the Lake George area of upstate NY, not, I believe, much time on the ocean. She's a trailersailer and I don't know if she spent much time sitting in the water, probably not. What I didn't see in the corrosion of my boat's CB, is more corrosion close to where the brass and iron come together. The pitting is pretty consistent across the surface of the cast iron. It looked like the bottom paint was applied a couple of times and I don't know if it was original to the boat. If the iron is the anode metal and the brass is cathodic to it, I would expect to see more corrosion close to their contact. Perhaps there was contact between the centerboard and the trailer. The boat is 47 years old.

-Will (Dragonfly)

 

[dLj]

When I bought my Mariner, the cast iron centerboard was pitted heavily under its very worn coating of bottom paint. There is a brass ring insert at the pivot point and the board hung on a heavy (1") brass pin with a steel cable for raising and lowering. Typical, I think. New Mariners built today by Stewart Marine out of Rockland Maine, come with glass centerboard.

Do you know that the centerboard is cast iron? Looking quickly over the designs of this boat, I don't know why they would have used cast iron. Perhaps cast malleable, but I don't see a design need to use cast iron. It's also not a shape that is screaming out to use cast iron...

Not that they didn't use cast iron, I don't know. Just asking.

Got pictures of the board, pivot and cable?

dj

 

[Will Gilmore]

Not that I know what I'm looking at when it comes to things like that, I don't, but it is referred to as cast iron by the Mariner Class Association and they just made a deal with a foundry to start making reproductions for owners of older Mariners.

I have 5 coats of TotalProtect barrier paint on mine and it still needs more to fill the pits.

-Will (Dragonfly)

 

[dLj]

Not that I know what I'm looking at when it comes to things like that, I don't, but it is referred to as cast iron by the Mariner Class Association and they just made a deal with a foundry to start making reproductions for owners of older Mariners.

I have 5 coats of TotalProtect barrier paint on mine and it still needs more to fill the pits.

-Will (Dragonfly)

There are many classes of cast irons. It would be interesting to learn what exactly they may be using. I ask because if you have pitting, that can have different effects depending upon what class of cast iron they are made from.

dj

 

[Will Gilmore]

I'm trying to work my way through these 5 chapters. We are spinning out our honey too. MAN! That's a sticky, messy job and we started with no idea of the kind of organization we needed to have here. Next time will be better. Still, 200+ pounds. Honey is very heavy. It would make a good ballast. It doesn't shift quickly and sinks in water.

Anyhow, I'm reading about the copper- based metals. Interesting how adding a little zinc to copper can improve on the alloy's corrosion resistance. Throughout the book there are references here and there about the difference in surface areas between the anode and cathode metals and their effect on corrosion. A small amount of cathodic metal may actually have a negligible effect on the anode metal.

So far, these chapters provide some useful information on specific materials and their possible uses, their standard compositions and so forth. They are worth having as a reference when choosing hardware, etc., but seem to offer little towards understanding corrosion or how to address it. Like I said, worth having as a reference, just tedious in trying to commit it to memory and digest it for learning.

-Will (Dragonfly)

 

[dLj]

I don't know if this is going to be "over the top" or as my daughters say - TMI... but in Colliers book he just touches on the cast irons. But @Will Gilmore has brought up that his center board is cast iron. (So - yes, I'm blaming Will for this post... )

The term cast iron is a generic term. It refers to a rather large family of materials differing quite a lot in their properties. In general, cast iron is an iron based alloy typically with carbon running up to about 4% and silicon running up to about 3.5%. There are, of course, exceptions to this.

Carbon is only soluble in iron up to about 1% to 2%, so the extra carbon typically precipitates out in the form of graphite. The form the graphite takes when precipitating out is fundamental to how the material behaves, along with whatever addition of other alloying elements that may be used for various property enhancements.

Collier mentions Grey cast iron, white cast iron, malleable cast iron and ductile cast iron in his chapter 8.

Grey cast irons are by far the most widely produced cast irons in the world of foundries. There are probably hundreds of alloys within this family. Most of them fall in the 20 ksi to 40 ksi tensile strength range but there are some alloys, called the high strength grey cast irons, running up to about 80 ksi tensile strength. These alloys are fairly brittle however, at least compared to steels.

White cast iron is formed one of two ways, either through rapid solidification or alloying. The white cast irons formed by rapid solidification are typically done in specified locations within a grey iron casting where in the parts use, there needs to be a hard, wear resistant location in the final product. White cast irons produced through alloying are the basis for making malleable cast iron. They cast the white iron, then do a thermal processing step on the casing to produce malleable iron. One of the difficulties for this material is it is limited in section size, at least the last I knew (it's been a long time since did work in this field). I would doubt either of these alloys would be used in Wiil's centerboard. I also think there would be rather limited used for this group to be used in the marine environment, especially in recreational boating.

Ductile cast iron, also known as nodular cast iron or spheroidal graphite cast iron is quite an interesting cast iron. Last time I was working in this area, I was working in austempered ductile irons. Those cast irons can achieve mechanical properties on a par with high strength steels, including ductility measurements. Just amazing for cast irons! I would not be surprised if ductile irons might make it into sailboat keels and the like given their performance. Plus you can add in alloying elements to nicely enhance corrosion resistance.

But I don't know what cast iron alloys are commonly used in our boats, anybody have knowledge about this?

dj

 

[Will Gilmore]

Hit a rock, bent the keel wing
A question on keel material seems to end with agreement to it being cast iron.

-Will (Dragonfly)

 

[dLj]

Hit a rock, bent the keel wing
A question on keel material seems to end with agreement to it being cast iron.

-Will (Dragonfly)

Like mentioned above, there are hundreds of cast iron alloys and several general groups. Saying it is cast iron is like saying it was made from stainless steel. there are cast stainless steels, wrought stainless steels and within those two huge groupings there are essentially 5 fundamentally different alloy groups with very different properties...

I cannot believe that keel is grey cast iron. It would have broken, not bent.

But it could easily be one of the ductile cast irons. Then, you'd have to know what ductile cast iron it is in order to then know how to go about fixing it. I'd read that thread but not knowing what the base metal is, I can't comment on how to fix it...

It also may not be a cast iron at all. It could also be cast steel... or.... lead... or....

dj

 

[Will Gilmore]

Aluminum alloys sound very interesting.
Collier talks about Almag 35, an aluminum casting alloy with magnesium. He describes it as having very good corrosion resistance. What does that mean? I didn't see it listed on table 4-1 of seawater corrosion, pages 20-21.

How amazing that combining two of the most anodotic metals together could produce a material that had "good corrosion resistance".

-Will (Dragonfly)

 

[dLj]

Alloying is complicated. You don't really get a linear response. Like this element is good at this, that element is good at that so when you put the together the new alloy is not necessarily good at this and that... If you get what I mean...

What is "good corrosion resistance"? So the answer to that gets really complicated. One of the things I do quite like about Colliers book is how he takes some complicated issues and simplifies them so the reader can begin to understand. But then when you get down to the more detailed questions it gets harder to find the answer.

What makes good corrosion resistance always depends upon where, under what conditions, in what specific application does this material perform as desired. As desired in itself is not easy to define. We like to say "the part will never corrode or break - ever!". But that is just not reality. Everything corrodes, everything breaks - eventually - more or less....

Typically, individual alloy systems are ranked against the same alloy system. When you start trying to cross over and compare different alloys, it's like comparing apples to oranges.

Anyway, more later, my daughter just showed up to go off with her for today.

dj

 

[Will Gilmore]

I was just reading the section on solders, chapter 12.
I have done a lot of soldering, both electrical and plumbing. I never knew there were different types of flux. Some are good at removing the oxide film while others are non-corrosive but require the surface to be cleaned more thoroughly.

I wish I had mie time to talk about this, but hopefully others will chime in.

-Will (Dragonfly)

 

[dLj]

Soldering and brazing are exactly the same thing. There is an arbitrary cut-off temperature of 840 degrees Fahrenheit. The two metals to be joined remain solid, a third metal - filler metal - melts and fills the joint between. There is no difference between the two processes, except if the filler metal melts above 840, it's called brazing, and if it melts below 840 it's called soldering. Not everyone agrees with the 840, so you will find this number a bit higher or lower in different places but they are all around the 840 mark. The American Society for Welding (AWS) uses 840 as the definition.

The difference between these and welding is that in welding, all three parts become liquid.

All the other terms he used are just vernacular found in different places as these techniques are ancient and knowledge of what's really happening has evolved. All the concerns Collier talked about - joint cleanliness, oxide free surfaces - apply equally to soldering, brazing and welding. There are many ways to achieve that in all three of those techniques.

Long ago, I used to make my own soldering flux. You go find a good pine tree that is oozing pine pitch - the nice solid amber kind - take the pine pitch and dissolve it in alcohol and voila! Great soldering flux. You apply it to the joint with a paint brush and solder away. Clean the joint post soldering with alcohol wipe and there you go, clean as a whistle - as they say.

Now we simply buy our fluxes, and there are numerous different kinds. Lots of proprietary formulations, lots of application specific formulations. For sure, Collier suggests that you know about this and clean your joints according to the flux used, excellent advice. The chemistry of fluxes is an entire world of study.

With all the above said, on my own boat, I try to stay away from soldering. The modern crimp connections with heat activated adhesives that make for a sealed joint are just so much faster and easier to use as well as making a superb connection, that soldering is just a thing of the past, from my point of view, as applied to marine electrical connections. In addition to the chemistry and the dissimilar metals concerns Collier raises, you also have the mechanical concerns. A solder joint creates a point for fatigue to initiate if you don't design the joint properly. In my mind, it is just so much faster - easier - less problems - to use the modern marine grade crimp connectors that soldering is just not worth the effort.

dj