All-male crew of a novel boat (5)

I believe the answer is:

three

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'boat' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for three that I've seen before include "Figure" , "... number of his "Steps to Heaven"" , "Subject of 1 9" , "There (anag.)" , "Number of Dumas's musketeers" .)

I've seen this clue in The Globe and Mail.

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