The most common and most likely answer to this crossword clue is the 6 letter word SAILED
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The straight part
We know that "went by boat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case went by boat = sailed.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 SAILED mean?
SAILED verb- To be impelled or driven forward by the action of wind upon sails, as a ship on water; to be impelled on a body of water by steam or other power.
- To move through or on the water; to swim, as a fish or a waterfowl.
- To ride in a boat, especially a sailboat.
- To set sail; to begin a voyage.
- To move briskly and gracefully through the air.
- To move briskly.
- Having a specified kind or number of sail.
- Having the sails set.