Steel Trim Tabs (original) on Aluminum boat

I am no expert but my guess is that they are poor grade of stainless steel, which a magnet will stick to.

The magnetic property of stainless steel is not related to its quality, only its composition.

I'm only trying to point out that some types of stainless steel rust

Steel tabs

The tabs on our boat were Steel as well and were one of the first places pitted. We converted to stainless which was an easy change. You wil find the rudder is the next place to look at converting to stainless as well.
The cost to engineer and fabricate my tabs was a bit south of a Boat unit.
I have an engineered drawing if you would find it helpful, just beware it is drawn for a 41 Regal.
Mark

"The trim tabs themselves have no corrosion on them (aside from at the mount hole for the actuator)"

Even 316 will show rust in the heat affected zone around a weld or where drilling has created a hot spot unless it has been properly passivated. It is the nature of the material and has nothing to do with its quality or other properties.

Stainless steel do rust, it is the fact that the presence of the chromium that provides stainless steel with the ability to repel permanent stains and keep looking fresh and clean over long period of time. The chromium essentially creates a protective layer on the alloy that prevents rusting and makes the metal resistant to any real damage. Essentially, the addition of nickel to the stainless steel compounds helps to strengthen the protective qualities of the chromium. The reason is that the presence of the nickel alters the physical structure of the stainless steel and removes or inhibits any magnetic qualities.

Lotsa technical info on stainless...

But AFAIK, all aluminum Roamers came with plain steel tabs. If you look at the galvanic series in seawater, aluminum and plain steel are more compatible than aluminum and stainless steels, the worst of which are further away (i.e. less compatible) from aluminum alloys than even copper or bronze in certain circumstances. If I had to guess, I'd say Chris Craft used steel because it could take the beating in that application and it's the most compatible option.

But it can rust, so you gotta keep up on the barrier coats and bottom paint.

Specking of trim Tabs.. I reticently acquired A 1968 Steel Roamer.. That will be run entirely in fresh water in the 9 to 12 kts range. I really can see no advantage of maintaining the tabs in that environment. I am I missing something??. I'm hoping to be able to adjust trim with fuel and other ballast techniques.

I'm not familiar with the handling characteristics of your particular boat, and at those speeds the effect of tabs are generally more minimal, but you want to be able to do more than just lay your boat to one side all day. You want to adjust to circumstances as they arise (raise the bow when running with the seas, lower it when running into them, lean into a beam sea, etc.). I've come through some inlets where the use of tabs was critical for maintaining control.