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Comment by qchris | Hacker News Reader

I don't know if there's a name for this phenomenon, but it's sort of like an invisible Chesterton's fence. "Just make them out of a different steel" feels like a idea that is elegant, but even as someone that's never built a ship, I have to imagine there's some good reason why they're built out the materials they are, and why a simple material change is unlikely to be a solution. Maybe I'm wrong (it's not like organizations haven't done dumb things before despite a having a good simple solution), but it really feels like that's probably not the case here.

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Stainless doesn’t really hold up in saltwater, with the exception of a few grades. The material properties (toughness, ductility, brittleness, weldability) can also be significantly different than non stainless.

Corten can work in less aggressive environments, but it has been known to fail to provide the expected protection in places with more acidic rain than was expected. Salt water is really aggressive.

Hot dip galvanizing does work, and is common for small boats, dock fittings, and other smaller items. There are also likely sacrificial anodes on the ship made of zinc.

There are many sacrificial zincs on ships, including in tanks.

I don't know about modern ships -- I suspect a lot of this is classified -- but as an example, the WWII Bismark had a hull which was around a foot thick, as armor.

(1) Rust wouldn't go all the way through. Surface rust isn't a problem.

(2) You want high-quality armor; toughness is key. Steel composition should be primarily chosen for toughness-to-weight

(3) And cost, of course.

Stainless would have been expensive, and given little upside, and potentially a lot of downside in terms of less effective armor plating.

Obviously, modern ships are entirely different (much less armor, actually, instead relying on active defenses), but I assume there are sensible reasons for materials choices.

The exact construction of modern ship hulls is definitely a secret, although perhaps not the most closely guarded one. There are plenty of photos of the Cole with a giant hole blown in it for example.

But modern ships generally don't have any amount of armor except against the smallest of gunfire. The idea being is that if someone gets close enough to shoot at you with a sizeable cannon you're already dead.

Modern missiles with explosive heads and get through anything with can make so there is no point to armor. In the battleship era you could get armor that would give your own guns trouble, but most battleships saw action against bigger battleships and good tactics meant they did okay.

The Navy would love armor that can stand up to modern missiles, but it isn't really possible, and the compromises in costs and inside space mean it isn't worth it. Maybe someday we will find a new material that would work, but for now ships rely on not getting hit.

Peacetime ships are also expected to last (Googling) 36 years in good condition.

I'm sure it was a concern in WWII, and that they took all steps they could to preserve their vessels, but I'm also guessing that as long as they weren't rusting so fast as to become junk in three or five years, they were much more worried about surviving combat than rust.

Why not coat the hulls with gold? As a noble metal, gold doesn’t have sufficient valence electrons to oxidize.

What could go wrong?

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