What does the cryptic crossword clue "Rotten bunch’s drunken exploits on board ship (3,7)" mean?

The wordplay uses an anagram. anagram of EXPISTOL (synonym="EXPISTOL") + SS (synonym="steam ‘ship’") = SEXPISTOLS The answer is SEXPISTOLS.

Rotten bunch’s drunken exploits on board ship (3,7)

Guardian Cryptic #29461 | 13 Down | 2024-08-14 flower