Stainless steel bolts in alloy casting: how to avoid electrolysis?

vas

vas

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hello,

subject says it all really!

Had an issue with my Lofrans Tigres windlass, with the stripper missing when I bought the boat back in 2011. In 2014, after a thorough rebuilt (of the boat as well as the windlass...) I fitted it again. A specialist welded new material on the windlass casing, and tapped new M8 threads for the new SS stripper.
So three years later, I tried to undo the stripper in order to remove the gypsy. After a lot of trouble the one bolt came out, the other wont move, just hammered and turned the stripper enough to remove the gypsy.
Examining the threads of the bolt that I managed to remove, it's obvious that somethings wrong, seems to have pieces of alloy in the threads, and in other areas SS thread is missing.

I wonder since these two dissimilar materials have to live together, and since another two tigres windlass in my pontoon suffer the same, is there any way to isolate the two materials?
Could I use teflon tape (the one we use for sealing pipes) or some grease? dunno!

Any ideas?

cheers

V.
 
With my Lofrans I removed all the fastenings and coated the threads and shanks with Duralec. Reports from others say that it reduces corrosion although I did not keep the boat long enough afterwards to find out for myself.
 
Similar query, same job, but carbon steel.

Would Copper Slip be any use on carbon steel socket head cap screws screwed into the alloy casing? I am assembling my anchor winch after refurbishment. Only two of the 10 original screws were seized with one requiring a machine shop to remove. The screws hold the end cover, which supports a drive shaft bearing, the caps are recessed and will be isolated from the outside environment with a polymer sealant.

I have both Duralec and Copper Slip available, the latter being my first choice.
 
Duralec (or Tefgel) is the stuff to use. Lanolin is effective if re-applied annually. Best answer is thread inserts: they're stainless, so any reaction is between insert and mother metal, rather than between fastener and thread. Many of the better mast manufacturers fit thread inserts as standard, albeit usually on larger sizes only (M8+), for this reason and for the greater strength and durability it provides.
 
thanks will order some today!

pity I wasn't aware of it, as I'll have to undo a few dozen bolts in the stanchions as well (ss bolts in cast alloy bases) and regulate them all again!

cheers

V.
 
pvb said:
Duralac is the stuff to use. It does work.
Click to expand...

BlowingOldBoots said:
Similar query, same job, but carbon steel.

Would Copper Slip be any use on carbon steel socket head cap screws screwed into the alloy casing? I am assembling my anchor winch after refurbishment. Only two of the 10 original screws were seized with one requiring a machine shop to remove. The screws hold the end cover, which supports a drive shaft bearing, the caps are recessed and will be isolated from the outside environment with a polymer sealant.

I have both Duralec and Copper Slip available, the latter being my first choice.
Click to expand...

Or for a close fitting joint like screw threads the PTFE based product Tef-Gel may be better. Certainly less messy than Copaslip or Duralac.

https://www.tefgel.com.au/

Available from the usual sources such as Force4
 
Duralac is based on barium chromate which is BRIGHT yellow. So, yes, although it's very effective it can be messy.

I used it on my Lofrans Cayman but I haven't pulled the studs out since to check. Following on-line comments about corrosion I put a sheet of PET plastic from a fizzy drink bottle between the windlass and its SS mounting plate. I also insulated the studs using nylon washers and shrink sleeve where they went through the mounting plate. Several years now and no signs of serious corrosion.
 
Duralac is certainly very messy and dries out so can make bolts hard to undo if left in place for a long time. I used Duralac on an aluminium casting and it worked but it was difficult to dismantle 12 months later even though corrosion had stopped. I smeared on more Duralac and let it dry out a little before smearing silicon grease on top of the Duralac and sliding parts back together. This worked well and has been repeated every year. I imagine it would help a lot for something that's not removed annually.
 
Having owned and refurbished a few Lofrans Royales, I still would recommend an annual strip down and overhaul whatever anti corrosion stuff you use. Any longer and you're asking for trouble. An overhaul doesn't take long if the set screws aren't seized but ages if they are.
 
Tefgel is the best I believe. It is being used by the pro's in preference to other products, is particularly liked by riggers.
 
Copperslip works for screw threads.
Tefgel works if the joint is fine enough.
Duralac works but can set hard and make things very hard to undo.
Any grease will help.
I agree it's still worth pulling things apart every year or two in many situations.

Another thing that works is threadlock used generously. Has its uses!
 
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