Thanks for all the comments everyone!
Isn't it interesting how sometimes a "chance" picture works out: I took several images of these boats racing each other back into the harbour, and tried really hard to avoid all the industrial stuff (and those tanks in particular), but in the end the only image worth keeping was this one with the tanks!
Torgny: you're right one day these tanks may become classics (strange but true): when I was young all our cities had "gasometers" scattered all round the town. I don't know if the word "gasometer" translates outside the UK at all: but these were really huge gas storage tanks that would move up and down depending how full they were. Very industrial, very much "form follows function" with no attempt to make them pretty, and yet somehow I used to quite like them :-) Nowadays I don't think there's one left anywhere.