Silicon Bronze vs. 316 Stainless Steel

[reeljob]

For screws in a 20' Simmons- which would be best? I've heard arguments for and againts both. Stainess supposedly cannont be in an anaerobic environment, silicon bronze eventually just disintegrates. Also sil. bronze is weaker than stainless???

Thanks

[JimD]

Judging by the responses to Sam F's thread on the same topic it'll prolly be six of one, half a doz of the other. Have you used bronze fasteners before? If not you'll find the steel a lot easier to work with. Bronze is very soft by comparison. The fasteners must be made a thicker gauge, pilot holes of the correct size must be scrupulously drilled, and it's surprisingly easy to strip the head of a bronze screw. Don't ask me how I know all this.

[reeljob]

Have you got a link for that thread? I didn;t see anything.

[JimD]

Have you got a link for that thread? I didn;t see anything.

Its only a few posts below yours, right here on the first page of building repair.

[reeljob]

Right under my nose... Considering the evidence provided in that thread- for something completely encased in epoxy/fiberglass, it really doesn;t matter what metal it is.

[Sam F]

Maybe encapsulation would work to protect any metal. It's a tempting option as ordinary steel drywall screws would sure be cheaper than either SS or bronze, but water has a way of getting into everything. I'd hate to rely on epoxy alone for corrosion insurance.

One thing to put in the decision process... bronze doesn't seem to damage wood when it corrodes like steel does.
Or maybe we should just use wooden pegs and forget about metal alltogether! :D

[pcford]

I rarely use anything but bronze.

I don't have enough nerve to bet that stainess is going to be ok. Using plain steel is just plain nuts. Once I had to replank a boat because it was fastened with steel. Waste of time and money.

[Jay Greer]

[ Stainess supposedly cannont be in an anaerobic environment, silicon bronze eventually just disintegrates. Also sil. bronze is weaker than stainless??? ] Quote

While stainless can suffer pocket corrosion in anaerobic use, It can be used where it will recieve oxygen. Mast & Deck fittings as well as hull use above the waterline. However, I really prefer bronze fastenings and hardware such as chain plates and mast tangs. Phospore Bronze plate is much much easier to form and cut than stainless and it does not need to be passivated. Stainless seems to have a nasty habit of developing pocket corrosion and cracking, even when in a fully oxygenated environment. So, I find bronze, tobin bronze, silicone bronze, phosphor bronze and manganese bronze to be more trouble free and in the long run more economic to use than stainless. If can be drilled, filed, polished, rivited, silver solderd and formed in the home shop on on the job site with simple tools. Where as stainless often requires a specialized shop to form and work it.
So far as silicone screws breaking down, the installer would do well to dip the threads in hot bee's wax or epoxy prior to instalation. Wet epoxy just as the screws are driven will lube and incase the threads in a protective barrier that will resist electric action and screw sweat that can start rot. Epoxy is messy so I prefer to pre dip my fastenings in bee's wax that does a better job of protecting the fastenings and is antifungicidal.
JG

[pcford]

I rarely use anything but bronze.

I don't have enough nerve to bet that stainess is going to be ok. Using plain steel is just plain nuts. Once I had to replank a boat because it was fastened with steel. Waste of time and money.

Right...actually use stainless for deck fitting, where plated brass was original.

[S/V Laura Ellen]

Using plain steel is just plain nuts. Once I had to replank a boat because it was fastened with steel. Waste of time and money.

Am there and doing that. Right you are, plain steel is just plain nuts.

If I could find the guy that used steel 70 yeard ago I would ring his neck!:D

[formerlyknownasprince]

The thin stainless bolt in this photo convinced me not to put any stainless back on to my boat below the waterline - more than happy to use it up top though. The larger bolts show what happens when metals are mixed - gal washers on stainless bolts for example. Until I started buying my silicon bronze from the USA, I was paying $2 a screw - and there are hundreds of them in my boat's new transom. Ouch.

http://www.imagestation.com/picture/sraid178/pe5f5b429e77df547e028b7f5a389c974/f31b4116.jpg

I would also like a chat with the miserable sod who fastened the deck beams on Grantala with iron spikes back in 1937/38 - had to replace every damn one of them.

Ian

[Thorne]

Wow! That's one convincing argument.

I know that mixing metals is bad, but what about copper and silicone bronze -- do they react badly if above the waterline? The silicone bronze has quite a bit of copper in it already....just wondering about some silicone bronze fittings I put on with copper rove rivets.

[reeljob]

Thorne- this might help. http://www.boatbuilding.net/article.pl?sid=06/03/14/2016224

[pipefitter]

Anerobic environment doesn't exist on a dry sailed boat.Stainless fasteners (316) or even 18-8 would work on dry sailed.Especially seated and bedded in epoxy.Only time I see anerobic environments is when someone hoses their parts with that armorall stuff or that one step wash and wax crap or corrosion block. It is evident by the greenish color of the stainless that leeches into everything surrounding it. On alot of the shrimpers,they used SS (large) ring shank spikes for the planking and they always looked new on decently maintained boats.There was some confiscated mary jane haulers that they broke up and all the SS fasteners above waterline were still like new,even after the boats had been sunk for a few years.

[reeljob]

Just out of curiosity, I stuck an 18-8 screw and a sil. bronze nail in some saltwater- the screw showed no corrosion, but the nail tunred green in a couple of days.

I'll probably go with 316 screws.

[pcford]

Just out of curiosity, I stuck an 18-8 screw and a sil. bronze nail in some saltwater- the screw showed no corrosion, but the nail tunred green in a couple of days.

I'll probably go with 316 screws.

How are you going to guarantee that water never gets to the screws?

Guess you are just betting on it, right?

[formerlyknownasprince]

Just out of curiosity, I stuck an 18-8 screw and a sil. bronze nail in some saltwater- the screw showed no corrosion, but the nail tunred green in a couple of days.

I'll probably go with 316 screws.

Phew - I'm glad your scientific approach to this prevented a major catastrophe - now, what to do with the collected wisdom from thousands of professionals?

[sdowney717]

the reason the 18-8 (304 and 305) ss screw did not show corrosion is enough dissolved oxygen was present in that water. But bury it in wood which is water saturated and the stagnant water loses oxygen and that 18-8 screw will crevice corrode. In 5 years it will be pitted with deep channels coring right thru the screw.
Now the 316 has resistance up to 5000 ppm salt in ocean water. Even this is not really enough to guarantee no failure but its better!

http://www.sandmeyersteel.com/316-316L.html

Alloy 304 stainless steel is considered to resist pitting and crevice corrosion in waters containing up to about 100 ppm chloride. The Mo-bearing Alloy 316 and Alloy 317L on the other hand will handle waters with up to about 2000 and 5000 ppm chloride, respectively. Although these alloys have been used with mixed success in seawater (19,000 ppm chloride), they are not recommended for such use. Alloy 2507 with 4% Mo, 25% Cr, and 7% Ni is designed for use in salt water. The Alloys 316 and 317L are considered to be adequate for some marine environment applications such as boat rails and hardware and facades of buildings near the ocean, which are exposed to salt spray. The Alloys 316 and 317L stainless steels all perform without evidence of corrosion in the 100-hour, 5% salt spray (ASTM B117) test.


If we could buy super duplex SS screws, they would be fine in brine for ever.
http://www.google.com/search?hs=0iI&hl=en&lr=&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=super+duplex+steel&btnG=Search

http://www.oceanint.com/content3/

[sdowney717]

I want to know
WHY CANT WE BUY SUPER DUPLEX SS FASTENERS!!

I mean what is the point wasting time with 316 or 18-8 seeing these screws are insufficient to the task and seeing that the super-duplex alloys have been around for 70 years now!


http://www.super-duplex.com/
The first-generation Duplex stainless steels were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.

[nedL]

I used a few stainless bolts in a boat that I rebuilt 25 years ago. I'm rebuilding her again now & was VERY suprised to find those stainles bolts corroded to the point that I could break them in half with my hands. (They were in her bottom fastening some small bilge keels. I'll be honest & say that even some of the original 60+ year old brass stuff faired better! I'm using nothing but copper (rivets) & bronze this time around, no more stainless in the hull. Just my observations & .002
Thorne - No problem mixing copper & bronze.

[westinghouse]

Hey reeljob - that green tarnish is your bronze's best friend. I'm not venturing into any more stainless debates, but that corrosive layer on the bronze keeps the good stuff in and the bad stuff out. I like bronze, and I like stainless - if it's stamped with both and S and a 316 stamp. Otherwise it could be anything silverish and shiny.

[pipefitter]

Damn,what are you guys putting your boats through. Mine begs for moisture by the time it has sat on the trailer for a few days.I did use bronze below the waterline but after seeing how fast it dries out after use,I doubt I would have problems with just using stainless. The sunken confiscated boats got their side planks wet every day when the tide came in and the stainless ring shanks were still intact,even where they had pulled away from rotted frames. I agree on using bronze in boat's made for sale if for no more than a selling point but if someone that ends up with a wood boat lets a trailered boat develop anerobic conditions such as letting fill up with rain water etc,the fasteners are the least of their worries.They are destined to have a disposeable boat. It amazes me to see how some advocate the use of premium fasteners but will also in the same breath advocate less than totally durable plywood or lumber or other materials. If you are to go with the ultimate fastener,best go with the ultimate best framing lumber and marine plywood. To use Si Bronze on okume plywood seems like overkill in the wrong direction.The lesser materials used, would suffer from anerobic conditions long before the fasteners would.

[htom]

Take that salt water bath and bring it to a rolling boil for ten or fifteen minutes to remove the dissolved oxygen, and then try your stainless & bronze soaking test.

[keelbolts]

Laura Ellen,
I was on your boat several times when Mr. Greenman owned her. Glad to hear she's found a good home.