The most common and most likely answer to this crossword clue is the 8 letter word SKYSAILS
S
K
Y
S
A
I
L
S
Buddy explains!
The straight part
We know that "nautical sheets" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nautical sheets = skysails.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 SKYSAILS mean?
SKYSAILS noun- The sail set next above the royal.