Aluminum sailboat rudder

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Hi I have to make an aluminum sailboat rudder for a friends father that is goin to be for salt water use. So after reseacrhing I have come up with 5052 welded with 5356 and 316 S.S. for the rudder shaft,  will these be good in salt water and is that the correct filler ?   This will be all tiged and covered with some kind of epoxy sealer and there will be 2 magnesium anodes on the rudder.Thanks Mike
Reply:It looks like the correct welding filler for the alloy.  Your biggest concern is isolating the SS shaft from the aluminum.  If the shaft is bolted to the aluminum you will have to use nylon bushings on the bolts and nylon washers as well.  Stainless bolts directly in contact with aluminum will seize up as the aluminum corrodes around it.  The anodes are a good idea but will not prevent stop the SS to aluminum problem.
Reply:Originally Posted by lotechmanIt looks like the correct welding filler for the alloy.  Your biggest concern is isolating the SS shaft from the aluminum.  If the shaft is bolted to the aluminum you will have to use nylon bushings on the bolts and nylon washers as well.  Stainless bolts directly in contact with aluminum will seize up as the aluminum corrodes around it.  The anodes are a good idea but will not prevent stop the SS to aluminum problem.
Reply:HMMM.....I would be thinking using more like 5086 (or something very close) would be the way to go.Better corrosion resistance for saltwater and generally stouter stuff from my experience.You can use the 5356 filler on it as well but you may want to do some research on that and make a phone call or two depending on just how much strain the welds will see.Miller Dynasty 700Miller 350P with Aluma-pro push-pullMiller 280 Dynasty with expansion card Dynasty 200 DXMigMax 215 Enuff power and hand tools to create one of anything..... but mass produce nothing!!!
Reply:Originally Posted by FusionKingHMMM.....I would be thinking using more like 5086 (or something very close) would be the way to go.Better corrosion resistance for saltwater and generally stouter stuff from my experience.You can use the 5356 filler on it as well but you may want to do some research on that and make a phone call or two depending on just how much strain the welds will see.
Reply:You did not say what the boat hull was made of.   If the boat is fiberglass or wood, and the rudder assembly would not be connected to any other metal part of the boat, your situation is a little simpler.  But what does the rudder shaft pivot in?  Bronze?  I would be concerned about the galvanic corrosion between stainless and aluminum in salt water.  (I would not worry in fresh water).   You probably will need to apply cathodic protection to the rudder assembly, or else the aluminum will tend to corrode away.   One common type of cathodic protection would be blocks of Magnesium, so the magnesium will disappear and protect the other metals.  Different metals in salt water tend to form a battery, and something will disappear, due to the current flow.Note that if you are mixing bronze (or copper), stainless, and aluminum, the problem will be larger.Look up "Galvanic Series", "Galvanic corrosion", and "Cathodic Protection" for more information.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge