silicon bronze vs stainless steel

On my restoration project I am replacing the transom....can I use SS screws to fasten to the plank ends where the bronze used to be? they will be hidden by filler and paint. it is a solid mohagonay transom attaching to a ply hull.
thanks.
Ralph

 

Stainless steel is a bad choice. It will get crevice corrosion in that application.

 

NO! NO! NO! Hot dip galvanized will last longer than SS in this application, but silicon bronze is best.

 

What do you guys think of ss ring nails for edge nailing fiberglass epoxy encapsulated strip planking?

 

Same basic problem....merely postponed.

Gander at all the derelects in your local yards. All our boats will look like that some day, coatings gone and sheathings perforated.

I use bronze ringshank for such applications, because if it has my builder's plate on it, I want it to be the one chosen for restoration.

The price difference between bronze and ss nails in a 20-foot boat isn't near as great as the satisfaction of knowing I gave the boat the best possible chance to survive.

 

I think the ideal fasteners for strip planking are epoxy staples. If they miss and come out the side the grinder takes care of it.

 

I think epoxy staples would be the cat's meow if your strips were small enough.

 

Ralph,

Don't add more ingredients to the galvanic soup than you absolutely have to.

Yoke.

 

I noticed the USCG " Guidance on Inspection, Repair, and Maintenance of Wooden Hulls" doesn't like the idea of stainless screws through "wet wood". Is Crevice corrosion the reason and just what is it? Where is it best to use silicon bronze, and where best for stainless? Thanks!

 

The answer would be a treatise on metalurgy. Stainless steel and bronze are families of metal alloys. There is no way to generalize. Rather, you need to specify the application and then choose the best alloy.

 

The publication doesn't offer any recommendation on a particular fastener, just a stearn warning against 304 stainless for sure and not so stearn on 316. For fresh water, what'd be the best fastening a plywood bottom to mahogany frames? How bout salt water with the same bottom, and if i could stretch this a bit farther, protect the bottom from worms? Thanks!

 

Are you screwing, nailing or riveting?

 

Stainless steel gets its corrosion resistance from a thin film of chromium oxide that forms on its surface upon contact with oxygen. This film can't form in anaerobic conditions such as those in your transom, and so the fastener's properties corrosion-wise in crevices, etc. more closely match those of mild steel. Bronze as an alloy is considerably more noble and thus less likely to rust out.

 

If you have bronze on your boat, be it: fasteners, strut(s), shaft, prop, etc. you have to use bronze again. I just ordered 2,500 #12 two inch, flat head, square drive boat screws (cut threads not rolled and with the proper shank size) The owner wasn't pleased with the cost of these over stainless of similar size, so a conversation ensued. I showed him what happens when you mix them or try to bury them in wet wood or under putty. It's amazing what a few bits of broken framing and some eaten up screws can convince.

 

We are using screws for all fasteners. The bottom is laminated meranti ply ( 2 1/4" layers) on mahogany frames (1x3), hull sides are 7/16 mahogany planks. Using life caulk at the joints, including sandwiched between the plywood layers. the entire bottom. Screws are all countersunk. Only epoxy involved is a barrier coating of the bottom, external only. We used stainless screws for everything, all fittings are stainless as well. Boat is 12ft and will spend most time out of fresh water. Too late for this one just wondering about the next one which may see some salt water. Also chines and sheer are also mahogany laminated with resourcinol glue. All Phillipine Mahogany. Thanks