Q to pro welders: mild steel chainplates to stainless rigging contact?

[Briis]

I have a strong mild steel sailboat. But one thing I am thinking of improving is getting rid of that annoying small but constant rust stain marks on my chainplates that contact the SS rigging.

Is it better to drill the (mild steel-) chainplate's holes a little bigger and:

a) insert a couple millimeter thick SS ring (with rightly sized center for the rigging pin) and weld it into enough bigger hole to fit welding

or

b) just drill a bit bigger and weld a little SS material inside the contact hole as filler and drill it round again to the right size so I have small SS coverage on the hole

This way I hope I can repaint it and no more galvanic rust stain between different materials. Structually it seems the a) option is stronger, but not sure since I am no metal specialist.

I assume on both cases the amount of SS on mild steel is proportionally small enough not to start galvanic reaction around the contact points inside the chainplates when welded with the correct SS rod(?) I learned this trick from Boreal aluminium yachts by observing their aluminim-to-SS chainplates that apparently use SS rings but not sure if they have to be SS rings on mild steel, since it's higher on galvanic table than the aluminium. So maybe the b) option as SS welded filler around the hole will do the trick as well.

Let me know how do you reckon is the correct way to do it.

[Lepke]

If you can find a ring with the needed inside diameter, drill the original hole .002"-.003" smaller than the ring. Freeze the ring and if necessary heat the hole and quickly press in the ring. When the temps equalize the ring is held securely without any welding required.

[Bowdrie]

Another option:
I assume that the jaw of a turnbuckle or toggle fits over the chainplate?
If so, one can use a bushing whose length just fits the width of the jaw and just slips thru the hole in the chainplate.
The bushing being simply a piece of stainless tubing cut to length.
Spares easy to have on hand and replace if/as necessary.
No press fits, no welding.
Hopefully there is lots of extra material between the top of the existing hole and the top of the chainplate.
IIRC, Skenes wants ~1.2 times the pin diameter of material above the hole.
I tend to go more, no reason to have pin holes close to the top of a chainplate, the depth of turnbuckle/toggles most generally will allow the pin holes to be further down than is commonly seen.

[Reefmagnet]

I've seen a sailboat that had stainless welded to places where abrasion of the paint was likely to cause corrosion and this idea works very well. In your case, I'd probably just consider sleeving. You can buy thin stainless steel tube that is used for for fuel and chemical lines and this could be easily cut and set with epoxy into a mild steel chainplate. You could also flare out the ends of the tube to help lock it in place.

[Yojimbo]

Briis,

I've done metal fabrication for 40 years. A mild steel to stainless contact will have galvanic corrosion and rusting regardless of welding it in place. Unless protected by hot dipped galvanizing this connection will weep rust and might even then. I have used nylon insert sleeves to isolate metal connection to prevent grounding and galvanic corrosion. You can't weld galv to SS- defeats the purpose. Can you design a connection with nylon sleeves to eliminate contact?

[edlithgow]

Deadeyes should be electrically isolating

[barcoMeCasa]

I chopped the top off my chain plates then welded and sandwiched stainless on top. Been annoying for years before that. Got lots stainless welded to steel, half chain links make great tie down points. Same as all the other metal, keep the weld join between stainless & mild steel painted it's been fine.

[Briis]

Originally Posted by Lepke

If you can find a ring with the needed inside diameter, drill the original hole .002"-.003" smaller than the ring. Freeze the ring and if necessary heat the hole and quickly press in the ring. When the temps equalize the ring is held securely without any welding required.

That'd be an idea. I've done very critical bearing replacements with the hot-freeze contrast spacing method in the past. But my concern would be if in time the sleeve would "wiggle" loose inside mild steel chainplate as the stays vibrate a little over time and have enough force to "loosen" any slack there is I reckon?

Also some air will get inbetween the SS sleeve and surrounding chainplate and I am back to square one - rust stains. This is the logic I thought maybe welding is a better idea - when done right I'll have a proper molecular melting/bond with no possibility of air getting inbetween anywhere.

Originally Posted by Bowdrie

Another option:
I assume that the jaw of a turnbuckle or toggle fits over the chainplate?
If so, one can use a bushing whose length just fits the width of the jaw and just slips thru the hole in the chainplate.

Yes, that's precisely my situation.

As you can see, there's some galvanic reaction going on as well - 30+ years has done it's part as well I reckon, but now it's every season at least 1-2X of repainging the area above the chainplates to keep them clean white below as on the pictures, but you'll get the idea:

Originally Posted by Bowdrie

The bushing being simply a piece of stainless tubing cut to length.
Spares easy to have on hand and replace if/as necessary.
No press fits, no welding.
Hopefully there is lots of extra material between the top of the existing hole and the top of the chainplate.
IIRC, Skenes wants ~1.2 times the pin diameter of material above the hole.
I tend to go more, no reason to have pin holes close to the top of a chainplate, the depth of turnbuckle/toggles most generally will allow the pin holes to be further down than is commonly seen.

Have to think about that. Maybe a "loose" SS tubing with well-covered non-conducting protection liquid helps that setup as well. But I see the downside is I'd have dismantle each pin-to-jaw and re-lube every couple of years or more often.

Originally Posted by Reefmagnet

I've seen a sailboat that had stainless welded to places where abrasion of the paint was likely to cause corrosion and this idea works very well. In your case, I'd probably just consider sleeving. You can buy thin stainless steel tube that is used for for fuel and chemical lines and this could be easily cut and set with epoxy into a mild steel chainplate. You could also flare out the ends of the tube to help lock it in place.

Have to look into it, as describe above, maybe adding a specialized nonconducting lube between the surfaces. But my concern would be higher maintenance.

Originally Posted by Yojimbo

I've done metal fabrication for 40 years. A mild steel to stainless contact will have galvanic corrosion and rusting regardless of welding it in place. Unless protected by hot dipped galvanizing this connection will weep rust and might even then. I have used nylon insert sleeves to isolate metal connection to prevent grounding and galvanic corrosion. You can't weld galv to SS- defeats the purpose. Can you design a connection with nylon sleeves to eliminate contact?

I though nylon as well, but not sure they take that tons of force the pins create to small area on the contact-point against the chainplate top?

My understanding is that when there's proportionally overwhelming amount (a small sleeve or welded ring-) of galvanically higher material (SS) surrounded by galvanically lower material (mild steel), then it does not create a noticable reaction.

Good example on my boat is the backstay chainplates - those seem to be full SS chainplates welded to otherwise mild steel body of the boat. No apparent reaction there. Not sure why the boat manufacturer didn't do the rest of the plates like that but chaning all chainplates to SS now would be too much work so those abovementioned methods maybe worth seek into.

Got to do more research on the nylon etc strenght as well. Maybe this is the solution I have been looking for if it sands up to the forces and keeps the SS and mild steel electrically separated. Since it's just not the pin, but also jaw is touching and rubbing agains the chainplate - nylon maybe the only way to go between the lateral jaw part when I think about it now.

My hope and aim would be that I could paint it over and have a non-rusting surfaces for a considerably long time.

[markxengineerin]

Have you tried occasional sprayings of Ospho or some other similar acid? This is how I eliminate all rust stains. Spraying frequency varies depending on how picky you are, but I'd say it's between weekly and monthly.

[Briis]

Originally Posted by markxengineerin

Have you tried occasional sprayings of Ospho or some other similar acid? This is how I eliminate all rust stains. Spraying frequency varies depending on how picky you are, but I'd say it's between weekly and monthly.

I've done that, but there's still slow galvanic reaction going on that slowly eats away the mild steel chainplate, as you can see on the above pictures, thus reducing strenght and integrity of the rig in my view. Albeit it's a very slow (as said, this is an over 34 years old boat already), but visually ugly and concerning process on deck thus in air and often saltwater covered environment.

Here's an aluminium boat example, that went on demanding sailing high latitudes for long a time:



You can see SS ring sleeved into an aluminium chainplate on aluminium hull. The same design in mild steel hull will probably be considerably stronger and longer lasting, but makes one think still.

As an alternative idea, I found one builder recommending G10/ FR4 phenolic sleeve. Anyone has experience with phenolic sleeves? They seem to fit the bill as they are great electrical isolators yet designed to withstand high pressures. Have to look into it I reckon.


Cheers,
Margus

[The Yacht Rigger]

Have you tried smearing tef gel or duralac all over the connection point, pin hole, sides of chainplate, etc, to isolate the connection between the SS and mild steel?

[Briis]

I extensively use both (tefgel and duralac) in weather-protected areas of contacts between galvanically different metals, but as said, they seem “high maintenance” way of solving this on a open air saltwater-washed deck (read: clean and relube too often to make it work). I’d prefer a longer lasting solution if possible.

[toddedger]

Anyone has experience with phenolic sleeves? They seem to fit the bill as they are great electrical isolators yet designed to withstand high pressures. Have to look into it I reckon.


Cheers,
Margus[/QUOTE]

Colligomarine.com uses what looks to be G10 or Fr4 phenolic sleeves in their aluminum rigging terminators where stainless pins sre used. I think they use them to insulate the two metals, and sometimes to bush down to allow for smaller clivis pin diameters. Give them a call to get the skinny.

[s/v michaela]

I use bronze bushings between the pin and chainplate boss. Prime and paint the chain plates. If the side gap is sloppy insert nylon cheek washers.You can probably get everything at McMaster Carr. Don't over think this.

[col50]

Originally Posted by Briis

I've done that, but there's still slow galvanic reaction going on that slowly eats away the mild steel chainplate, as you can see on the above pictures, thus reducing strenght and integrity of the rig in my view. Albeit it's a very slow (as said, this is an over 34 years old boat already), but visually ugly and concerning process on deck thus in air and often saltwater covered environment.

Here's an aluminium boat example, that went on demanding sailing high latitudes for long a time:



You can see SS ring sleeved into an aluminium chainplate on aluminium hull. The same design in mild steel hull will probably be considerably stronger and longer lasting, but makes one think still.

As an alternative idea, I found one builder recommending G10/ FR4 phenolic sleeve. Anyone has experience with phenolic sleeves? They seem to fit the bill as they are great electrical isolators yet designed to withstand high pressures. Have to look into it I reckon.


Cheers,
Margus

Phenolic (as in Linen re-enforced Phenolic) is good insulator only when it is dry, but it absorbs water readily.