Skunk, that's a good point about the tabs. I didn't even think about that. I guess, thinking more about this, tabs are not a "sink your boat" item if they fail so maybe that's why they're not covered/discussed under the ABYC spec. And, sure, it's not like SS fittings are just going to magically rot away in short time. In your case, they're not fully submerged all of the time so there's VERY little risk, if at all.
But I still think that with something that can sink a boat, and is submerged 100% of the time, it's a wiser choice to use something that you will never have to think about. Plus, with thru-hulls... while you can easily and quickly check the outer part of the thru-hull (the mushroom head), inspecting the interior of the barb is much harder to do... and that's also a thinner part which of course would suffer from catastrophic failure earlier/sooner.
It's still an interesting point, though. We know that SS suffers from crevice corrosion - that's widely known and even seen on many of our boats for fixtures above the waterline. But it's kind of a head scratcher when you then think about the tabs again. I'm just thinking outloud here, but it might have something to do with STAGNANT water (less O2 in it)... water that gets into a crack/crevice and isn't "flushed out" continually with fresh ("new") water. I HAVE seen SS screws that secure underwater fixtures start to rust and pit around the edges. Not a lot or often, but I have come across it.
Inboard boats and sterndrive boats have SS shafts that are submerged all the time (but no stagnant water surround them, obviously).
