Is stainless suitable?

[Scarboroughsloop]

My boat is larch planking on oak frames and she has a canoe stern. The rudder tube is currently galvanised steel and is corroding and so obviously I want to get this replaced. I have spoken to a well known shipwrights in the area who have suggested a replacement in 316 stainless. I am not very good with metals and their various forms of corrosion but does sound like a good idea as my very limited knowledge suggest it is perhaps not an ideal metal for this application?

 

[DoubleEnder]

Not ideal. Stainless can corrode if there is not an adequate supply of oxygen - ie flowing water. I can't remeber the technical term, but it will be problematic.

Replace it with galvanized? The old one lasted a long time, I guess, and it will be cheaper by far.

How big is the boat? You could go for something in plastic/GRP.....? Not a purist solution, however.

Bronze is by far the best. But it will be very pricey. Don't ask how I know

 

[Scarboroughsloop]

The boat is 28' long. My preference was for bronze and I would change the stock to bronze at the same time to avoid any dissimilar metal issues.

GRP (along with carbon fibre) has also crossed my mind but I believe the manufacture to exactly the correct dimensions is very difficult.......

 

[Peterduck]

You are governed by the metal that is the fastenings of the hull. If it is fastened by copper rivets, then you are really obliged to go with bronze. You will probably be able to use the old tube as a foundry pattern. Talk to the owner of the non-ferrous foundry that you plan to use, and ask what needs to be done to the existing tube to turn it into a usable foundry pattern.
Peter.

 

[oldharry]

Not a wooden boat I know, but the Trident 24 (60's GRP design) was built with stainless rudder tubes, and I have yet to hear of one that has failed.

Many wooden boats have stainless propshafts without problems, and anaerobic corrosion of the s/s is far more likely in the outboard bearing than on a rudder stock which is not such a tight fit.

Not saying it is right or wrong for a wooden boat, I dont know for certain - just that a lot of wooden boats have stainless prop shafts and get away with it, so with proper bonding it does not seem to be a problem.

I never had a problem with using stainless shafts on my many wooden boats over the years, except one which suffered slight anaerobic corrosion of the shaft inside the outboard bearing.