each girl seems to wear them differently.
some observations:
yukikaze - looks like a torpedo tube launchers
tenryuu - probably the bridge with attached weapons
kitakami - funnel/chimney
kaga - mast that functions as a quiver
ayanami, fubuki - chimney and mast
chitose - seaplane catapults
for most cases, mecha_musume or machinery is used for tagging these unless we want to be specific on the ship's parts.