Aethulred:
Electricity makes Hydrogen rather cheap to produce.
Not really. This eats as much energy as burning it back releases plus overhead. It's a lot. So it's easy, but not cheap.
In an industrial center, sure, it's not big deal. But e.g. it can't be produced at a whim on a ship in the middle of an ocean (unless it's a nuclear submarine or something), since then it comes from the ship's total fuel stores (through engine and generator.)
And in limited quantities it's often going to be much more mass- and volume- worthy to generate hydrogen from an acid.
Also, production is only where the trouble starts. A worse part is storage and transportation - it's very hard to keep as liquid, so the only option are strong (thus thick, thus heavy) tubes. I.e. it's as bad to haul around as helium (but not as prone to leaking through "sealed" things) or oxygen (but less dangerous).
Aethulred:
as has been recently shown, the Hydrogen in the HINDENBURG isn't what caught fire, rather the paint used to coat the fabric is...
Naturally. Hydrogen is
inside... initially. The problem is
spreading fire. Helium blows it off and locally smothers, while hydrogen, well...
Aethulred:
So pure hydrogen or mixed with an inert gas is reasonably safe. A ship could use it as a separate flotation device/hull underwater and a rupture would be a lot less risky...
Compared to what? If you have a ship in water,
air is quite floaty.
But keeping anything floaty below waterline worsens the balance - normally people put
ballast there.
Then again, if it can double as an anti-torpedo bulge, it may be "worth it" once munitions under waterline become a big threat.
Aethulred:
The issue is how do use use hydrogen.
If you don't
need it already, why bother with it in the first place? ;)
Aethulred:
It burns extremely hot and so most engines have problems with it.
It's hot because it gives
very little of gas products (2/3 of spent hydrogen
and oxygen total), which is another reason why it's an inherently Bad Idea as fuel for internal combustion engines that use expanding gas.
So, not much of extra functionality on the side. The only good uses for hydrogen not involving a chemical factory or space-industry-grade expenses are:
1) Floating in air (balloon/blimp).
2) Very hot flame (cutting torch, unusual light sources).