Should stainless steel inside a rudder be coated for corrosion inhibiting?

[Wind River]

I am in the process of rebuilding my rudder on my Hudson Force 50.

There are parts of the stainless stock that have corroded badly and I am replacing all of these components. Most of this stainless steel is encapsulated in the fiberglass. Is it recommended to prime or coat the stainless before glassing it into the rudder?

Water always seems to get into a rudder somehow and I would imagine there would be a lack of oxygen there leading to corrosion. So, what product should be used?

I have seen Zinc Chromate primer for a corrosion inhibitor on aluminum but is it for stainless also? There was a yellow coating in some places that looked like this kind of primer.

If I used Awlgrip 545 epoxy primer, will the vinylester resin have adhesion problems to that?

Should I just clean it and glass over it with nothing?

[Emmalina]

Stainless requires oxygen to remain stainless ! Having said that its better than most things. I would just clean it up and glass on top. Thats what I did with my rudder and used 304 on parts below the water line !

[Wind River]

Originally Posted by Emmalina

Stainless requires oxygen to remain stainless ! Having said that its better than most things. I would just clean it up and glass on top. Thats what I did with my rudder and used 304 on parts below the water line !

Why did you choose 304 over 316 stainless?

I made all my parts with 316L.

[Emmalina]

Originally Posted by Wind River

Why did you choose 304 over 316 stainless?

I made all my parts with 316L.

Because under water there is no difference to the level of corrosion between 304 and 316 and its a lot cheaper !

[coopec43]

Originally Posted by Emmalina

Because under water there is no difference to the level of corrosion between 304 and 316 and its a lot cheaper !

"Therefore, it is preferable to avoid using stainless steel in applications where it is regularly exposed to stagnant or still water for extended periods. Ideally, high-quality silicon bronze, cupronickel, Inconel, or non-metallic alternatives should be used, particularly for fasteners and raw-water plumbing. The fasteners used to secure struts, strainers, and other underwater hardware, for instance, should be bronze rather than stainless steel. If stainless steel must be used in such an application, for a custom-made strut or shaft log for instance, it should be fabricated from the most corrosion resistant marine alloy available, 316L or 317L.

https://www.passagemaker.com/channel...-and-corrosion

[transmitterdan]

Originally Posted by Emmalina

Because under water there is no difference to the level of corrosion between 304 and 316 and its a lot cheaper !

Not based on my experience. I would only use metals made of 316 SS, Titanium or bronze below the waterline.

[pcmm]

Originally Posted by transmitterdan

Not based on my experience. I would only use metals made of 316 SS, Titanium or bronze below the waterline.

Other factors often come into play when choosing between 304 and 316L where I am (Canada) just finding 316L is a massive challenge. No one stocks it and when you find someone that does the cost is a small fortune! I can replace 304 fittings (often) twice for the cost of one 316L fitting. Have to factor in the age of the boat too. If the boat made it 40 years on a 304 rudder, do you think it has another 40 years left in the boat? 30? 304 will likely be fine, but like everything else keep an eye on it. I see this a lot with the current fascination with using titanium for chainplates. Really is the boat going to last another 40 years? does it really make sense to go to that extreme?

[coopec43]

Selection of 316, 304 and 303 types of stainless steels for seawater applications

https://www.bssa.org.uk/topics.php?article=100

[Reefmagnet]

I could be wrong, but 316 performs a lot better than 304 in water temps of around 25 deg C or above. Below that, they are pretty much on a par in regards to saltwater corrosion resistance.

[a64pilot]

I’d sand or head blast it and epoxy coat it and then use it.
Zinc chromate won‘t do anything in my opinion and won’t likely adhere very well either.
Stainless isn’t one of the better metals to use, but it’s cheap, widely available and easy to work with.
Try welding or machining titanium for example.

Yes encapsulating it in epoxy does of course rob it from O2 contact, but hopefully will keep if from seawater contact too.

[Wind River]

I found that the 316L stainless cost about 25% more than 304. In this project that amounted to about $100.

I am acquainted with a sailor that has a Force 50 whose rudder stock parted with the rudder 300 miles out from Hawaii. His experience has led me to check mine out while I have the opportunity. My solid 60mm shaft has two places that I can stick a small pick a 1/2" into the solid material. That does not inspire confidence that it will go another 40 years. Other areas of corrosion are much more obvious.

The thought that the original 304? stainless lasted 40 years is a compelling one but for a little more money I can have a small degree more confidence that it may outlast the boat. Those that buy these types of boats fall into two categories. Those that know most are severely degraded and those that find that out. I hope that the next owner of this boat will appreciate the extra effort in making sure any repairs were done to a higher standard than the original build. Maybe it will fetch a little more money on resale, maybe it will just sell faster than a similar boat. Either way I will have a bit more confidence and satisfaction than I would have had otherwise.

So, with that out of the way, should I coat the stainless for added corrosion protection or not. If so what should I use?

[Pete7]

Out of curiosity how much does a rudder stock in silicon bronze or titanium cost?

Pete

[robwilk37]

built mine using 2205 duplex SS. the entire assembly (shaft and frame) that is embedded inside the rudder itself was scuffed and coated in epoxy. the only likely place for water ingress is the top if the rudder where the shaft exits so i relieved a 1/4" channel about 1" deep and filled with polysulfide on the assumption it will be a bit flexible over time and maintain a watertight seal. should out-last me i think...

[Copacabana]

Originally Posted by Wind River

I am in the process of rebuilding my rudder on my Hudson Force 50.

There are parts of the stainless stock that have corroded badly and I am replacing all of these components. Most of this stainless steel is encapsulated in the fiberglass. Is it recommended to prime or coat the stainless before glassing it into the rudder?

Water always seems to get into a rudder somehow and I would imagine there would be a lack of oxygen there leading to corrosion. So, what product should be used?

I have seen Zinc Chromate primer for a corrosion inhibitor on aluminum but is it for stainless also? There was a yellow coating in some places that looked like this kind of primer.

If I used Awlgrip 545 epoxy primer, will the vinylester resin have adhesion problems to that?

Should I just clean it and glass over it with nothing?

Have a look at this video (and the others on his rudder rebuild). I think the expanding epoxy foam looks a great solution for rudders and I imagine it will result in a dry rudder core.

https://www.youtube.com/watch?v=ZMB0RUCwFvY

[guyrj33]

to answer the question asked, yes coat everything with epoxy. I'll also suggest using epoxy for the glass layup.
additionally the welds in your picture look like they corroded first. I know there is a process of cleaning welds that will help delay corrosion, maybe it's called passivization or electro-polishing? The important point being there is a treatment that's done after the datinless is welded up.