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Old 21-11-2015, 10:37   #16
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Re: Steel boat with stainless steel chainplates

I have really enjoyed reading the many good comments posted above by everyone. While I don't own a metal boat, I have wanted one for years (they have a magnetic appeal to me) and try to read and learn as much as I can about them with the hope of having one in the future. It has been a few years since I read the books I bought on building steel boats , so my knowledge on them is admittedly limited, rusty (pun) and only by study, not by owning one. So I appreciate when you "metal heads" share your anecdotes.

Travis McGee.
Thanks for adding the details on your build and the 20 year maintenance or lack of maintenance required on your boat. She sounds well built (and painted)! And I really like the external design, and found it interesting that it is a bilge (twin) keel boat. From the photo it appears there is a bulb on the bottom of each keel. Is that a Van De Stadt design? Also, do you have any links to any photos of the boat I can see (externals, deck, house, cabin)? I enjoy looking at steel boats of all makes to get ideas and many "self built" boats have unusual things I find interesting. Also I liked your description of a possible cause of the weeping rust from stanchions. It makes sense that the paint would get stressed and crack leading to some water intrusion and rust.

Cheechako
I liked what you wrote too. Water inside the stanchions is a possible cause of oxidation.

Steve77
I think the Amazon boats look great. I spent many minutes admiring one I saw online a few years ago. Wish I could have one too.
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Old 21-11-2015, 10:50   #17
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Re: Steel boat with stainless steel chainplates

Crevice corrosion occurs above and below the waterline. It happens where ever stagnant, oxygen deprived salt water stays in contact with SS. Most common area is where the SS chain plate passes through the deck on FRP boats. With a leak, water is trapped and stagnates. Welding SS to mild steel pretty much eliminates the possibility of trapping water. Using stainless welded to mild steel is quite common in areas of high wear like cap rails and chain plates.

Bronze against mild steel is a recipe for disaster. Unless the two metals are totally isolated from each, you will have made a battery with a little saltwater electrolyte and galvanic corrosion will result.
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Old 21-11-2015, 11:06   #18
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Re: Steel boat with stainless steel chainplates

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Originally Posted by steve77 View Post
I went back the other day and looked at the specifications for our boat, and came upon something that surprised me. We own an Amazon 49, a steel boat built in Surrey (outside of Vancouver) Canada.

The specifications state "Chainplates: stainless steel chainplates welded through deck with undersupports running to the frames."

I went on deck with a magnet, found that the chainplates are nonmagnetic, and, I presume, stainless. They are painted the same color as the deck, and I never knew they were a different material.

My first question is, is this normally the way it is done? I always thought the chainplates were the same steel as the rest of the boat.

Second, is there anything I should be aware of to prevent future problems? Since they are welded in place, removal for inspection is impossible. I never worried about crevice corrosion or anything else on the chainplates since I thought they were mild steel. I just made sure there was no rust anywhere around them. Now I'm wondering if I need to be looking for anything else.

Any thoughts appreciated. Cheers!

Steve
Welding stainless to mild steel is quite reliable. Typically the joint is made with a filler material midway between the two materials. 308 filler with 316 SS for example.

The main concern in the heat affected zone is how well the chromium is distributed. Too much heat results in uneven migration which will lead to very aggressive corrosion.

Warning signs occur between the edge of the weld filler material and the parent material. It will usually be very visible. Glass bead blasting and polishing will highlight any issues.

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Old 21-11-2015, 11:34   #19
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Re: Steel boat with stainless steel chainplates

I've experienced no problem with stainless welded to mild steel, I normally use SS rod. When my deck scuppers rusted out, I replaced them with plastic. I use a lot of plastic pipe around the boat, and make many things by using parts of PVC pipe sliced opened and heated to make flat sheets and then bent into whatever shape you need. A heat gun is one of my most used tools. The scuppers/deck drains rusted out, they were plain steel pipe welded to the steel deck gutter just under the bulwarks. I cut a rectangular hole where the drain pipe used to be, then cut a 3/8 thick piece of Plexiglas larger than the hole, cut a hole in the center of the plexiglas to get a good solid friction fit for the top of a 6 inch long by 1 1/2 inch PVC pipe. This gives the new drain pipe connection for the rubber hose to the thru-hull fitting. I then bolted this flat plate with sealant to the underside of the steel deck. This gives me a window providing some light in a very dark portion of my engine room in addition to a never rusting deck drain. It's much easier to keep the flat surfaces and plexiglas joint painted.
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Old 21-11-2015, 14:20   #20
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Re: Steel boat with stainless steel chainplates

If it ain't broke, don't fix it.
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Old 22-11-2015, 10:23   #21
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Re: Steel boat with stainless steel chainplates

Thanks, everyone. You can tell I'm not a welder, or a metallurgist. I was not aware this method was so commonplace.

We will haul out soon, and I will check the cockpit scuppers, through hull nipples, and other areas of the boat for other stainless fittings.

We have had Orontes II almost seven years, and I thought I pretty much knew everything there was to know about her. I guess I'm still learning.

Cheers!

Steve
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Old 22-11-2015, 14:03   #22
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Re: Steel boat with stainless steel chainplates

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Originally Posted by Steady Hand View Post
I am no expert, but using stainless for the drain pipes and some applications seems better than mild steel due to the difficulty of maintaining with paint (e.g. due to inaccessible inner surfaces) that would likely corrode if mild steel, or if subject to abrasion which would wear off protective paint.
I think you are spot on with the deck drains and some of the others on my boat that are stainless. 'Fairleads' (that's the term I couldn't think of the other day ) are perhaps simply because the rope going through them will repeatedly wear off any paint and so they would rust away pretty quick if they wern't stainless. Now I know they are stainless, I intend to polish them up nice and pretty.
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Old 23-11-2015, 08:45   #23
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Re: Steel boat with stainless steel chainplates

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Originally Posted by Rustic Charm View Post
I think you are spot on with the deck drains and some of the others on my boat that are stainless. 'Fairleads' (that's the term I couldn't think of the other day ) are perhaps simply because the rope going through them will repeatedly wear off any paint and so they would rust away pretty quick if they wern't stainless. Now I know they are stainless, I intend to polish them up nice and pretty.
Now you have it!

Don't worry about occasionally forgetting a term for some boat parts. I do that too, despite many years of study and sailing. In fact there are still many thing on boats (especially the old traditional boats I admire) for which I don't know their proper names, and I don't think I am alone.

That's part of the fun and challenge of sailing, learning enough jargon to be understood. Always more to learn.
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