Stainless Steel Rigging on a steel yacht

[Wideocean7]

I have had a rigging survey on a steel yacht that I am hoping to buy. She has the usual stainless steel stays which have been directly connected to mild steel deck tangs/chainplates (from which the vessel is made). Over time galvanic corrosion has badly corroded the tangs, which must now be replaced. That involves exposing the interior headliners to check corrosion of the chainplates and to repair/replace the tangs - might be a cutting/welding big job. When undertaking repairs/replacement, is there a reliable way of isolating the stainless steel from the mild steel to reduce or prevent future galvanic corrosion of the tangs? Thanks!

[hpeer]

I have 2 steel boats. 33’ -1985 and 44’ - 1987.

The 33 has 1/4 mild steel tangs. Slight rust.

On the 44 the chain plates were replaced with Ss plates by the origional owner. No rust.

In my experience isolation devices fail or fail to stop the corrosion.

If it were me I would install as chain plates.

[SOLAR SUPPORT]

Hi, Isolating the Stainless Steel riging from the steel body is possible. If you can make a stainless steel plate that riggings attached to it, then isolate the plate's bottom by laying a thin, hard plastic or epoxy based isolator between the steel body and the stainless steel plate. Make sure that screw bolt joints are also isolated with nonconductor washers.

[steve77]

Our steel boat has stainless steel chainplates. They were welded to the frame as part of original construction.

With SS chainplates you do not need to worry about clevis pins wearing through the paint and causing rust. It may not be a quick project, but it seems to me like the way to go, rather than trying some means of isolation.

Cheers!

Steve

[roverhi]

The corrosion is just normal rust. The pins of the rigging abraid the paint and the mild steel rusts. Has almost nothing to do with whether it's stainless steel against mild steel. Fairly common to weld stainless pieces into mild steel boats where the paint will be scratched, abraded, chipped etc. on a regular basis typically on cap rails, chocks, etc.

[Wideocean7]

Thanks all. Very helpful comments. Unless I read it wrong, it sounds like ss chain plates, welded and isolated from the steel hull are the way to go.

[hpeer]

Originally Posted by Wideocean7

Thanks all. Very helpful comments. Unless I read it wrong, it sounds like ss chain plates, welded and isolated from the steel hull are the way to go.

Can’t quite wrap my head around the concept of “welded and isolated”.

What I meant was to either weld in new SS chain plates OR to weld SS tabs/extensions onto your existing chain plates.

This eliminates th e need for isolation.

The other option is to try to isolate your rigging pin from the mild steel plates. Which I don’t know how to do. You would have to drill out the existing plates oversize and put in isolating bushings. But you need to be careful in drilling the plates that you don’t weaken them too much.

Hope this is helpful.

[Wideocean7]

Thanks hpeer. This sort of feedback is always helpful. As it might come across, I am quite new to steel yachts. (although have been sailing coastal and oceans for many years, mainly on GRP and timber yachts). So this is my way of learning! I had perhaps misinterpreted that somehow the ss chainplate would be isolated, yet welded from the mild steel hull. I am not a welder so don't know if that's even a possibility. If I were to install ss chainplates, would that not just transfer the galvanic corrosion risk to the hull frame/plate where those metals bond? Or in practice is that the way it's done and then it's a case of monitoring any corrosion and then replacing corroded frame/plate steel when it comes around again?

[Jim Cate]

I am pretty sure that the corrosion that you report is not in fact galvanic in nature. The bloody mild steel bits are just rusting when any protective coating is disturbed. They would rust just the same if you were using mild steel shackles and pins. All this talk of electrical isolation is not well supported IMO.

Jim

[Wideocean7]

Hopefully my attempts at uploading a photo have worked. Shows what the corrosion looks like. It seems to have gone beyond just rust. I'm happy to be proved wrong 'though!

[hpeer]

Jim Cate is right, it’s abrasion removing the paint.

You are right, that piece needs to be replaced badly. Always hard to tell from photos but my gut says it’s well beyond replacement stage.

Your best inspections tools are a ball pean hammer, heavy full shank screw driver, and a bad attitude. Hit that sucker with a dozen really good sacks and see what you find left.

I’ve heard it argued that if you weld SS to mild steel the ion exchange still occurs and eventually degraded the material. That may be so, but if it does it is at a much slower rate than what occurs otherwise.

My personal observation is that I frequently gets small spot of sever corrosion where I have a bit of SS near some mild steel, but not in full contact. For example a wood hatch cover with a SS hinge pin, 3 are as new, 1 rusted right through the 3/16” deck about a 1/2” diameter, under the paint.

IMHO this is a pretty good and practice book.

https://www.amazon.com/Metal-boat-ma.../dp/B0070QRME4

[Wideocean7]

Thanks Guys. I scoured the world for Scott Fratcher’s book and now covet a hard copy from the UK. It’s a goldmine for me at least. Only problem I have with it is that some of the defects he is illustrating aren’t very obvious in the photos.

[MicHughV]

I can give you my perspective on it...

My steel Roberts ketch had mild steel tangs and an all stainless steel rig.
The tangs were blasted, zinced and painted as was the rest of the boat.

Once tension is applied to the stay via the turnbuckle, the tension will invariably cause the turnbuckle pin to eat away any paint or zinc at the upper inside part of the tang hole in the bearing area.

What I did, once the rig was properly rigged and tensioned everywhere, I smeared a dollop of 3M's 5200 around the turnbuckle pin and tang to try and make this a watertight and airtight seal.
This will seal off this connection for the most part, though some movement can be expected, but the 5200 is flexible enough to withstand this minor movement.

Even after pounding thru' seas for several weeks at a pop, there was very little rusting to be seen, though some rust weeping/staining could be noticed on some of the tangs, but this was easily cleaned with some ospho rust neutralizer.

After owning that boat for the best part of 15 years and countless sea miles, those tang/turnbuckle areas were never a rust problem area, other than the staining I mentioned above.

At anchor or tied up to a dock, these were never a problem area.

When one is sailing, the leeward shrouds will usually sag a little and I believe this was the issue on my boat as some tension is released which in turn reduced the pressure on the tang from the turnbuckle pin, possibly causing enough of a gap for rust to bleed through.
But this was a problem only noticed on a long ocean voyage.
For the most part it was a "cosmetic" issue and not a " structural" issue at all.

Trust this can provide an alternate point of view.

[NSboatman]

Replace the chain plates with 316L (the L is important - denotes more readily weldable) grade stainless steel chain plates. They can be directly welded to mild steel, using the correct rods (409L, iirc).

Bog standard setup, very reliable.

Where you may find rust bleed issues in this setup is where the paint on the mild steel stops and the stainless welds start. Common area requiring frequent de-staining.

But- with that kind of corrosion showing in the chainplates; it’s a bit of a flag for other parts of the boat. Make sure you inspect ruthlessly.

[MicHughV]

When I finally sold my steel boat after 15 years, the new owner had it shipped by road elsewhere, which meant the masts had to come down. This offered me an opportunity to visually inspect all the metal tangs.

To my surprise, once all the 5200 had been removed, all the mild steel tangs were in as near as new condition. For sure, I could see where the turnbuckle pin had caused some wear inside the upper inside of the tang hole and some tangs exhibited a tiny amount of rusty metal inside the hole, but nothing of concern.

In the same breath, my stanchions were all stainless and these were welded directly to the hull. The lower 3" of the stanchion had another stainless steel sleeve fitted over it and welded in place, to give the stanchion a bit more "meat"at the base. These were welded to the hull using stainless steel welding rod.

As the above posts mentions, after a period of time, rust bleeding was noticed at the paint/weld junction. Again, this was mostly cosmetic in nature and a nuisance from time to time.

If purchasing a used steel boat, it would well worth the exercise to have all the tang/turbuckle's disassembled for inspection. If there is little noticeable wear an option would be to re-assemble with a healthy tablespoon of 5200. This worked well for me.