Silicon Bronze Screws/Bolts with Stainless Steel Fittings?

[tontoOx]

I am about to start buying deck hardware for the wood/marine ply boat I am in the process of building.

I have read that silicon bronze screws/bolts are the best to use in a marine environment. However, what about using silicon bronze screws/bolts with stainless steel fittings (probably 316 but some might be 304)? I know that dissimilar metals in contact with each other can cause electrolytic action between the dissimilar metals and hence corrosion, but how bad would it be between silicon bronze and stainless steel? And are there any workarounds to deal with the problem?

Thanks.

 

[rangebowdrie]

I've not had any problems using silicon bronze fasteners to attach stainless deck fittings.
But I would never mix metals for underwater use, like a seacock/thru hull/bolts.
Don't use bronze on aluminum parts.
The dearth of quality bronze deck hardware in todays world his highly lamentable.

 

[tontoOx]

I've not had any problems using silicon bronze fasteners to attach stainless deck fittings.
But I would never mix metals for underwater use, like a seacock/thru hull/bolts.
Don't use bronze on aluminum parts.
The dearth of quality bronze deck hardware in todays world his highly lamentable.

Thank you. I read somewhere on this forum:

"A small amount of the more noble metal surrounded by a much larger amount of the less noble metal will result in a very slow corrosion rate."

Q1. Would silicon bronze screws be less noble than stainless steel 304/316?
Q2. Do you put something on the threads to seal the threads e.g. blue loctite thread locker?

 

[rangebowdrie]

Silicon bronze is more noble.
Standard practice is to coat the fastener with some kind of Polysulfide, and using the same as a "gasket" to bed
the hardware part against its mounting surface,, no reason to have any "sealant" products on the parts of bolts/nuts that are interior and not exposed to weather.
Sealant is for keeping water on the outside of the boat,, preventing leaks into the substrate/interior.
No reason at all to use any kind of "Locktight" product(s) for anything of that nature.
A complete discussion of sealants, their applications/usage, and properties approaches infinity.

 

[rangebowdrie]

This is but one of scores of tables/charts on Anodic/Cathodic metals;
galvanic chart - Bing images

 

[tontoOx]

Silicon bronze is more noble.
Standard practice is to coat the fastener with some kind of Polysulfide, and using the same as a "gasket" to bed
the hardware part against its mounting surface

Thanks. Do you mean something like this for dipping fastener threads in?
BoatLIFE Life Calk Sealant - 10.6 fl oz Cartridge | BoatLIFE https://www.boatlife.com/product/life-calk-cartridge/

A complete discussion of sealants, their applications/usage, and properties approaches infinity.

Okay, understand. I feel more comfortable now about using silicon bronze fasteners with stainless steel "deck" fittings.

 

[kapnD]

Does the above wisdom remain pertinent underwater?
Say a SS strut, or a SS rudder with a bronze bushing/gland?

 

[rangebowdrie]

The copper based metals are always superior in underwater usage,, (of course speed boats and outboards and all kinds of craft use non-copper metals in many applications,) I'm speaking to "traditional" craft used in salt water.
Probably the most well known example of mixing metals underwater is using a bronze propeller on a stainless prop shaft.
We allow that combo by the generous use of zincs, another combo that's common is bronze rudders with stainless shafts, and we monitor the corrosion, (or lack thereof,) by regular replacement of the zincs.

 

[ferahunt]

Hey there! I'm new to this forum, but I couldn't resist chiming in on this thread. Silicon bronze screws and bolts are definitely the way to go in a marine environment - they're super durable and resist corrosion like a champ. As for using them with stainless steel fittings, you're right that dissimilar metals can cause some electrolytic action and corrosion. However, the difference between silicon bronze and 316 stainless steel isn't too extreme, so you should be okay. If you're super worried about the hardware, you can always use a barrier material like Tef-Gel or Duralac to prevent direct contact between the metals. Hope that helps!

 

[gonzo]

Stainless screws with a bronze drum has been used for decades on turnbuckles with no problem. I don't see any issue with deck fittings.

 

[Thomas Meek]

On the subject of dissimilar metals and use of barrier paste.
Would it at all be necessary to use duralaxc between anodized alu and anodized alu? this will be for a boom vang and will have some SS 316 fasteners which i will obviously use duralac on but where the lower head connects to the vang tube is both alu so would it be good practice to add some duralac there anyway?

 

[rangebowdrie]

Being hired to work on boats for others, I got in the habit of using various anti-seize compounds for virtually all jobs that involved threaded fasteners, it's just cheap insurance.
With things that have flanges that rest/sit upon metal, (like a pad eye on a mount or a vang bracket to the mast,) I've used thin pieces of Neoprene, (1/16th",) and slathered both sides with something along with the fasteners, (gas pipe tape works also).
Keeping water from getting between parts is always good practice.