13 across
Mainly
competent
rating
(4,6)
Mainly competent rating (4,6)
hints
0
checks
0
hints
The whole clue is the definition (& lit or double definition).
How the clue works
The whole clue is a whimsical definition of an ABLE SEAMAN, a naval rating. "Mainly" hints at the sea (the main), "competent" gives the sense of ABLE, and "rating" is the naval rank, all rolled into one cryptic picture of a capable sailor.