The picture that came out is kind of ridiculous.
I have plastic and have NEVER had a problem. Plastic is nice because it does not kink
Because there are lots of pipes inside submarines carrying water. Submarine hulls are fairly sturdy things, pipe-fittings are not, so it is much more likely that a seawater header would fail catastrophically than the hull would. And, yes, it looks good in movies, and is fairly inexpensive to simulate.
Because water spraying around is much more dramatic than air hissing. Regards, Dan
