The most common and most likely answer to this crossword clue is the 6 letter word WHERRY
W
H
E
R
R
Y
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The straight part
We know that "Boat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boat = wherry.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WHERRY mean?
WHERRY noun- A light ship used to navigate inland waterways.
- A flat-bottomed vessel once employed by British merchants, notably in East Anglia, sometimes converted into pleasure boats.
- A liquor made from the pulp of crab apples after the verjuice is extracted.