There are some disadvantages to replacing the Catalina 22's bronze keel pivot pin with stainless steel, particularly in saltwater. But it's not necessarily a bad idea.
1. Galvanic corrosion:
Your assembly consists of:
Keel: Cast iron
Hangers: Bronze
Original pivot pin: Silicon bronze
Proposed replacement: 316 stainless steel
Stainless steel is generally more noble than bronze and cast iron in seawater.
Replacing the bronze pin with stainless could increase galvanic corrosion of the cast iron where the metals contact each other.
However, the original bronze-and-iron combination already presents a galvanic corrosion concern.
Galvanic corrosion is worth considering, but it isn't necessarily a dealbreaker.
2. Crevice corrosion
This is potentially the more significant concern.
Stainless steel depends on oxygen to maintain its protective chromium oxide layer.
Inside the keel's pivot hole, oxygen availability can be limited.
Under these conditions, even 316 stainless can experience localized crevice corrosion.
Silicon bronze doesn't have this particular vulnerability.
3. Wear characteristics
Bronze is an excellent bearing material.
A stainless pin running directly against bronze hangers could work, but the harder stainless pin may transfer more wear (& galvanic corrosion) to the hangers.
With the original bronze pin, wear is more likely to occur on the relatively inexpensive, replaceable pin.
That's a useful characteristic of the original design.
4. Strength
Here's where stainless has an advantage.
A suitable stainless alloy generally offers greater mechanical strength than conventional silicon bronze.
However, the Catalina 22 uses a substantial 1-inch-diameter pivot pin.
The original bronze pin is already designed to support the keel.
I haven't found evidence that additional pin strength is necessary.
5. What Catalina actually specifies
Catalina's original documentation identifies the pivot pin as silicon bronze.
Interestingly, Catalina Direct sells a stainless steel retrofit bushing for the cast-iron keel, but continues to supply a bronze pivot pin.
But this application too is susceptible to crevice corrosion due to the lack of available oxygen.
That suggests stainless steel can be incorporated into this assembly successfully, although it doesn't establish that a stainless pivot pin is preferable.
I'd retain the silicon-bronze pivot pin.
It's the cheaper "fuse" in the system.
Not because stainless is inherently unsuitable, but because bronze offers an excellent combination of corrosion resistance, bearing characteristics, and proven service history.
And a replacement bronze pin is only about $27.
...Just my opinion for what it's worth.
My intention is to be helpful.
