usage 'boat' instead of 'ship'

[paradigma]

English Grammar Error, Intermediate level

ESL/EFL Test #11 "I really wonder", question 10

Never mind we're all in the same ship now and we shall have to work together in order to find a solution.

(a) Never mind
(b) in the same ship
(c) have to
(d) solution

English Grammar Error, Intermediate level

ESL/EFL Test #11 "I really wonder", answer 10

Never mind we're all in the same boat now and we shall have to work together in order to find a solution.

Correct entry: in the same boat
The error was: (b) in the same ship

You have not found the error.
Never mind we're all in the same ship now and we shall have to work together in order to find a solution.
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we use 'boat' instead 'ship' in this sentence because of the expression 'in the same'. Don't we? or is it an idiomatic expression?

paradigma

[Mister Micawber]

.
That's right-- 'in the same boat' is an idiom.
.
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Native English teacher at Mister Micawber's