“When the boat sank, their investment went up in smoke.”
When something goes up in smoke, it is completely lost, as if it had burned up in a fire. It is especially fitting if it actually was lost in a fire. However, the fire is just a metaphor, so it could be lost in any way.
「船が沈んだら、投資金は水の泡だ。」
何かが up in smoke（煙と消える）と言うと、火事で燃えてしまったかのように完全になくなってしまう事です。本当に火事で焼失してしまった際の言い回しにぴったりですが、火はあくまでも例えなので何を失くした場合でも使える表現です。
