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チョコラ たのむ 船内のようすをみてきておくれ
Chocola, please check the state of the ship.
Father! There's no oil!
We made a big slip up. It looks like this tanker wasn't carrying oil.
I like the phrase "dai miss" (big miss). It could be "big mistake", "screw up" or "really messed up". I probably should have gone with "we really slipped up", but I didn't.
What the, we went through all this trouble for an empty tanker!!
I think that there's a big difference between how manga uses punctuation and how it's used in English. Both English and Japanese are tonal languages, where inflection of the voice changes the meaning of the words. A rising inflection at the end of the sentence can turn it into a question, and a falling inflection can make it a flat statement. The problem is how to illustrate that when the words are written. With English we have "!" and "?", while in Japanese we have "ka" (a spoken question marker) and the small "tsu" mark following "--". As Japanese writers are exposed more to written English, they start picking up on the question and exclamation marks, but these are not used in quite the same way as in English.
I think also that surprise or incredulity are used in different situations between the two cultures. So, in the above scene, when Dracula yells about the tanker being empty, in the Japanese text we just have the "---" followed by the small "tsu" at the end. This makes it look like he's just bellowing angrily "You're saying we got the wrong tanker!!". Yet, as English speakers, if we look at the original Japanese balloon and compare it to the English translation, we're going to tell (even if subconsciously) that the English version uses "!?" and the Japanese doesn't. In part, there's going to be a disconnect because we're expecting surprise, not anger, and because Tezuka doesn't use "?" and "!" the same way we do. Anyway, I used the "!!" here for emphasis.