The most common and most likely answer to this crossword clue is the 7 letter word STAITHE
S
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The straight part
We know that "where the sailors tie up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case where the sailors tie up = staithe.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 STAITHE mean?
STAITHE noun- A riverbank
- A fixed structure where ships land, especially to load and unload; wharf; landing stage.
- An installation built at the railside or nearby for the storage of coal unloaded from wagons.