The most common and most likely answer to this crossword clue is the 4 letter word AHOY
I've seen this crossword clue in The Guardian
A
H
O
Y
More clues leading to the result AHOY
- Barbara with no money finally making call at sea
- Opener from admiral meeting boat?
- Crafty greeting applies Henry of York sources
- Hello, sailor!
- Boatman’s way of hailing Araucaria: his leading place a towering old man here
- Midday hail at sea
- Hail in a part of Orkney
- What sailors sometimes call a boat
- What a sailor may call a cyclist
- Hail on the waters
Buddy explains!

The straight part
We know that "Hail" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hail = ahoy.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 AHOY mean?
AHOY noun- An utterance of this interjection.
- To hail with a cry of "ahoy".
- Used to hail a ship, a boat or a person, or to attract attention.
- Warning of something approaching or impending.