"They like travelling by ship."
Translation:Họ thích đi du lịch bằng tàu thuỷ.
Is there really any difference between thủy and thuỷ? Actually my keyboard driver does not allow the second version but always automatically replaces it by the first one.
The former is an older convention based upon harmonising the aesthetic while the latter goes for the main vowel in the word (usually).
No. That's just convention. Whether the accent should be put on u or on y is still controversial at the present.
When I had to choose the best translation out of three the correct answer was missing "thuỷ". I luckily knew it was místake.
Actually, it is not a mistake. Ship can be tàu or tàu thủy. We use tàu thủy if we want to emphasis or to distinguish with tàu hỏa/xe lửa (train). Thủy and hỏa are both Sino-vietnamese, thủy means water, hỏa means fire. So, when someone says tàu, we will firstly think about ship. Hope it helps!