The most common and most likely answer to this crossword clue is the 7 letter word DREDGER
I've seen this crossword clue in The Times
D
R
E
D
G
E
R
More clues leading to the result DREDGER
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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 = dredger.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 DREDGER mean?
DREDGER noun- A vessel equipped for the removal of sand or sediment from the seabed.
- One who fishes with a dredge.
- A dredging machine.
- A container with a perforated lid, used to sprinkle sugar or flour.