Fabricate new rudder post and fingers, what material?

I am back at it again. Finally took my rudder completely apart. The post is shot. The post is 1 7/8 inch OD and about .15 wall thickness. 49 inches long and made of stainless. Welded to the post are three 1 1/2 wide fingers made of plain steel. (as I hear, this was common).

I am seeking advise on what alloy to use for the assembly. I have no way of knowing what the original alloy was, but that does not really matter. Rudders like this are ubiquitous.

I know that SS can suffer crevice corrosion when in a low oxygen environment, so this is my main concern. The post has some deep pitting at the point where it exited the rudder and this is the reason I need to replace it.

I also have to decide on whether to copy the original design and use fingers or to come up with a new design. For instance, rather then use 3 fingers I could use a single plate, (like a mini rudder).

I did a quick search of the online metal suppliers and found 316 tube, welded and seamless.

There are a few decisions to make:

what material 316, 316L, 2250 Duplex SS, or something else
what wall thickness
welded, seamless...
where to get the materials from.

HELP! (lol)

Thanks guys...
Hopefully there are 2 pictures attached

 

Only monel (NiCu) or 316L (poor second choice and maybe the OEM material). Unless your flipping it for a sell, everything else is will have the same problem. Depending on the strength needs a true 302/304 is an option.

https://www.nickelinstitute.org/~/M...theSelectionandUseofStainlessSteels_9014_.pdf

 

Are you sure the wall thickness is only .15 in?

 

I measured it with a decent caliper. od is 1.9 and wall i s .15 or .145.

Now I am thinking that I was off about the post being 1 7/8. That would measure 1.875 and this measures 1.9.

That would be consistent with inch and a half pipe, more or less. There are always tolerances.

I started checking around and have found that 1 1/2 inch pipe is available in 316 and 316L. Seems that schedule 80 with a wall thickness of .2 is available. TW metals lists schedule 160 with a wall thickness of .28.

Best part is that the price is just below 100 dollars plus shipping. Tube was over twice the price. I am awaiting responses to me inquiries as to availability and what other alloys are available and at what price.

I an crazy busy right now, but am excited about the possibility of pipe.

Now I have to decide on the ribs. I can use ss for finger ribs as they were before. (they were plain steel) Or I can weld a plate, like a mini rudder. I checked the prices for plate and it would be much more then the ribs, made of 1/4 by 1.5.

I am also concerned as to the strength of welds on the center line versus welding on the edge (tangent?). With the center line weld it is much easier for me to reassemble the rudder. The edge welds make it a little harder to put it back together. It is still doable though.

Here is a picture of that "mini rudder" type frame. (not mine of course)

 

This is where I get my stainless:


http://www.speedymetals.com/pc-2546-8259-14-x-1-12-316-stainless-steel-annealed-pickled.aspx